Cooling results without Thermostat vs. with
- Thread starter turbo nasty
- Start date
turbo nasty
Turbo Dojo / MNTR
- Joined
- Jul 19, 2001
I thought the thud thud thud was the water bong cooling the engine ..... We need more flow...no more smoke...no more inhaling. No more smoke flow and inhaling....oh wait we forgot to exhale.
Warning: Do not read further without some form of chemical assistance:
@ mdshr,
Hope you’re all recovered from “beer-thirty”
Thanks for your input your post is informative and relevant although I’m not sure where completely on the same page, but it’s an interesting topic!
If Q_eng increases more than Q_rad, then the steady-state coolant temperature (T_coolant) will be higher. If Q_rad increases more than Q_eng, then the steady-state coolant temperature (T_coolant) will be lower. It is not inherently obvious which of these two outcomes will occur on a given engine/radiator combination.
I see what you are saying, by changing the flow rate of the cooling system, a higher heat transfer rate will be result on both sides. And if the heat transfer rate into the coolant changes more significantly than that from the radiator, then coolant temperatures would increase.
Let me know what you think, but I think the above can only be a transient response and cannot be steady state. Look at the radiator side, both Delta T and heat transfer rate are higher than before. If at steady state then this would mean that the engine has lost efficiency, while coolant temps have increased, which I don’t think is possible..
As for the constant heat transfer assumption used in my previous post:
My personal thought is that opening up a thermostat would not instantly change the thermal efficiency of an engine significantly enough to undermine a constant heat transfer assumption, but my personal thoughts are irrelevant to this conversation! So, to help clarify the issue further, I’ll try to re-derive the equations to include the effect of engine efficiency change below:
The heat rejection coefficient (I made that up, not sure what to call it) into the cooling system can be written as a smooth continuous function of engine coolant temperature.
Thus, the non-constant heat transfer rate is defined as a function of coolant temp such that,
Solving equations 1, 2’ and 3 (1 and 3 from previous post)yields the steady state coolant temperature,
We can see from this equation that when our engine is less efficient (ie f(t_coolant2) >> 1 ), t_coolant2 will get higher…. Therefore, we will investigate the equation for extreme changes in efficiency wrt temperatrure.
Looking at equation 4 only f(t_coolant2) is a function of t_coolant2, so,
As the limit of t_coolant2 -> t_coolant1, f(t_coolant2) = 1 (note that this limit valid from both sides)
Thus for large changes in inefficiency
All that this means in laymen's terms is that,
1. 1. The more the efficiency decreases with temperature change, the less the coolant temperature drops.
2. 2. Temperature will never increase or t_coolant2 < t_coolant1
Let me know what you think if you get a chance, if you want.
@ mdshr,
Hope you’re all recovered from “beer-thirty”
Thanks for your input your post is informative and relevant although I’m not sure where completely on the same page, but it’s an interesting topic!
If Q_eng increases more than Q_rad, then the steady-state coolant temperature (T_coolant) will be higher. If Q_rad increases more than Q_eng, then the steady-state coolant temperature (T_coolant) will be lower. It is not inherently obvious which of these two outcomes will occur on a given engine/radiator combination.
I see what you are saying, by changing the flow rate of the cooling system, a higher heat transfer rate will be result on both sides. And if the heat transfer rate into the coolant changes more significantly than that from the radiator, then coolant temperatures would increase.
Let me know what you think, but I think the above can only be a transient response and cannot be steady state. Look at the radiator side, both Delta T and heat transfer rate are higher than before. If at steady state then this would mean that the engine has lost efficiency, while coolant temps have increased, which I don’t think is possible..
As for the constant heat transfer assumption used in my previous post:
My personal thought is that opening up a thermostat would not instantly change the thermal efficiency of an engine significantly enough to undermine a constant heat transfer assumption, but my personal thoughts are irrelevant to this conversation! So, to help clarify the issue further, I’ll try to re-derive the equations to include the effect of engine efficiency change below:
The heat rejection coefficient (I made that up, not sure what to call it) into the cooling system can be written as a smooth continuous function of engine coolant temperature.
Thus, the non-constant heat transfer rate is defined as a function of coolant temp such that,
Qeng2 = f(t_coolant2) * Qeng_1 (2’)
Note that Qeng2 must equal Qeng1 when t_coolant2 = t_coolant1, thus f(t_coolant1) = 1. This is important…Solving equations 1, 2’ and 3 (1 and 3 from previous post)yields the steady state coolant temperature,
t_coolant2 = t_coolant1 * hrad1 / hrad2 * f(t_coolant2) – Tamb * (hrad1 / hrad2 * f(t_coolant2) - 1) (4)
We can see from this equation that when our engine is less efficient (ie f(t_coolant2) >> 1 ), t_coolant2 will get higher…. Therefore, we will investigate the equation for extreme changes in efficiency wrt temperatrure.
Looking at equation 4 only f(t_coolant2) is a function of t_coolant2, so,
As the limit of t_coolant2 -> t_coolant1, f(t_coolant2) = 1 (note that this limit valid from both sides)
Thus for large changes in inefficiency
t_coolant2 = t_coolant1 * hrad1 / hrad2– tamb * (hrad1 / hrad2 - 1)
Which is the same as the constant efficiency equation as in the previous post.All that this means in laymen's terms is that,
1. 1. The more the efficiency decreases with temperature change, the less the coolant temperature drops.
2. 2. Temperature will never increase or t_coolant2 < t_coolant1
Let me know what you think if you get a chance, if you want.
Let me try it this way... Perfectly intelligent board members have reported that their coolant temperature went down when they removed the thermostat. Other perfectly intelligent board members (including the poor OP, who has probably long since abandoned ship) have reported that their coolant temperature went up when they removed their thermostat. Doesn't that tell us something? I know that many of them are probably on the bong, but I am still thinking that they can accurately read their temperature gauge, right?
Everyone except bryesh should stop reading now and go back to their chemical of choice. If you read this, you will instantly grow a pair of plastic-frame eyeglasses on your face and a hideous pocket protector in your shirt pocket...
Again, I think one of the assumptions you used is simply incorrect:
The heat rejection coefficient (I made that up, not sure what to call it) into the cooling system can be written as a smooth continuous function of engine coolant temperature.
Thus, the non-constant heat transfer rate is defined as a function of coolant temp such that,
Qeng2 = f(t_coolant2) * Qeng_1 (2’)
Note that Qeng2 must equal Qeng1 when t_coolant2 = t_coolant1, thus f(t_coolant1) = 1. This is important…
Qeng is not only a function of coolant temperature. Among other things, Qeng is a function of coolant temperature and "h", the heat transfer coefficient. "h" in turn is very complicated to calculate, and in heat transfer "h" is usually found from empirical test data. What I can say is that in most cases, "h" increases as the flow rate of the coolant increases. So, Qeng is a function of at least coolant temperature and coolant flow rate (among other things). Simple example - if you put a hot piece of metal in front of a fan, the air will cool it. If you turn the fan to a higher speed, it will cool the hot piece of metal more quickly, even though the temperature of the air didn't change. Right? When the air speed increased, "h" increased, and the hot piece of metal cooled more quickly (Qmetal increased). Similarly, Qeng is a function of both the coolant temperature and coolant flow rate. This is in contradiction to your assumption above.
Once you remove your assumption, your math doesn't work out. I know it's counter-intuitive, but it's the truth - when you remove the thermostat, the coolant flow rate goes up (assuming no cavitation or other weird stuff). When it does, the radiator will suck more heat out of the coolant. Also, the coolant will suck more heat out of the engine. The heat transfer coefficient "h" for both increases. Without testing, I can't say which one increases more.
Back to beer and praying that my Wolverines get their sh_t together at UConn...
Everyone except bryesh should stop reading now and go back to their chemical of choice. If you read this, you will instantly grow a pair of plastic-frame eyeglasses on your face and a hideous pocket protector in your shirt pocket...
Again, I think one of the assumptions you used is simply incorrect:
The heat rejection coefficient (I made that up, not sure what to call it) into the cooling system can be written as a smooth continuous function of engine coolant temperature.
Thus, the non-constant heat transfer rate is defined as a function of coolant temp such that,
Qeng2 = f(t_coolant2) * Qeng_1 (2’)
Note that Qeng2 must equal Qeng1 when t_coolant2 = t_coolant1, thus f(t_coolant1) = 1. This is important…
Qeng is not only a function of coolant temperature. Among other things, Qeng is a function of coolant temperature and "h", the heat transfer coefficient. "h" in turn is very complicated to calculate, and in heat transfer "h" is usually found from empirical test data. What I can say is that in most cases, "h" increases as the flow rate of the coolant increases. So, Qeng is a function of at least coolant temperature and coolant flow rate (among other things). Simple example - if you put a hot piece of metal in front of a fan, the air will cool it. If you turn the fan to a higher speed, it will cool the hot piece of metal more quickly, even though the temperature of the air didn't change. Right? When the air speed increased, "h" increased, and the hot piece of metal cooled more quickly (Qmetal increased). Similarly, Qeng is a function of both the coolant temperature and coolant flow rate. This is in contradiction to your assumption above.
Once you remove your assumption, your math doesn't work out. I know it's counter-intuitive, but it's the truth - when you remove the thermostat, the coolant flow rate goes up (assuming no cavitation or other weird stuff). When it does, the radiator will suck more heat out of the coolant. Also, the coolant will suck more heat out of the engine. The heat transfer coefficient "h" for both increases. Without testing, I can't say which one increases more.
Back to beer and praying that my Wolverines get their sh_t together at UConn...
I don't even take asprin. Beers and women are as far as I take it. (granted, I take them pretty far )
The original reason I typed out that book was because I wanted to try and show that a cooling system has more going on that "I need big ass radiators and fans that suck like Angela Smith (and can cause localized numbness)".
Yes, these cars are quirky as all hell, and yes, they will run you ragged if one of the ducks are facing the wrong direction.... BUT, when a controlled test goes against the laws of physics, it's not a good idea to just accept it. The only way a controlled test with one change can have a result that doesn't agree with the laws of thermodynamics is if there's something else going on. Personally, when I get a result like that, I HAVE to know why. ESP if the reason why can/will change when I'm 200 miles from home.
)The original reason I typed out that book was because I wanted to try and show that a cooling system has more going on that "I need big ass radiators and fans that suck like Angela Smith (and can cause localized numbness)".
Yes, these cars are quirky as all hell, and yes, they will run you ragged if one of the ducks are facing the wrong direction.... BUT, when a controlled test goes against the laws of physics, it's not a good idea to just accept it. The only way a controlled test with one change can have a result that doesn't agree with the laws of thermodynamics is if there's something else going on. Personally, when I get a result like that, I HAVE to know why. ESP if the reason why can/will change when I'm 200 miles from home.
I agree with all of the heat transfer discussion which I think is a secondary effect, but the problem is really a pumping problem. I think two separate issue are being confused here. The problem with taking the Tstat out is how it effects the pressure drop of two connected cooling loops. The fluid flows from high pressure to low pressure. The system has two parallel loops, one through the block and one through the radiator. The restriction through the Tstat increases the pressure drop through the radiator, creating a balance between the pump suction from the block and the pump suction from the Tstat and radiator. With the Tstat gone, you have now changed how much coolant circulates through the block compared to the radiator with no ability t regulate it, and this also has a dramatic effect as pump speed changes. The Tstat works minimize the effect giving the proper mixing based on the designed system pressure drop curves, the pump output curves, and on temperature.
I have seen revenge of the nerds and was marginally insulted! Now back to the math!
Thanks for the reply mgmshar, I see your point but I still can't get the math to work out!
So, let’s try a different approach. I still can’t come up with anything showing coolant temps increase, so I’ll set up the steady state equations from fundamental principles, and you can tell me what assumptions to use that will produce a higher coolant temp! I know that finding heat transfer coefficients is not straight forward, but once that is known, the basic equations are.
A heat engine, such as an otto cycle, converts thermal energy Q, to mechanical power Q_mech. We define the engines mechanical efficiency, eta, such that
So,
So, by assuming that T_coolant2 > T_coolant1, we get
1. 1. Q_alt2 < Q_alt1, (If coolant temps are higher at state 2, then Q_alt2 > Q_alt1)
2. 2. Q_mech2 > Q_mech1 (It takes equal power to push a car down the highway, steady state)
3. 3. eta2 < eta1 (as you said, this is why engineers added thermostats)
I can’t think of any exceptions to these, so let me know if you do and what your thoughts are (mistake somewhere??, those danged subscripts are especially pesky). By assuming that tcoolant2 < tcoolant1 then they all work out. So that has to be the conclusion if the math is correct.
Thanks for the reply mgmshar, I see your point but I still can't get the math to work out!
So, let’s try a different approach. I still can’t come up with anything showing coolant temps increase, so I’ll set up the steady state equations from fundamental principles, and you can tell me what assumptions to use that will produce a higher coolant temp! I know that finding heat transfer coefficients is not straight forward, but once that is known, the basic equations are.
A heat engine, such as an otto cycle, converts thermal energy Q, to mechanical power Q_mech. We define the engines mechanical efficiency, eta, such that
Q_mech = eta * Q. (10)
A percentage of this wasted energy goes into the cooling system and is defined as Qeng. The rest, Q_alt, goes a number of different places (ht transfer not throught radiator etc).So,
Q = Q_mech+Q_eng+Q_alt. (11)
As a result of combining 10 and 11 we get,Qeng = Q_mech (1/eta – 1) – Q_alt. (12)
Now, assuming a steady state of a car going down the highway at constant speed after temps have equilibrated, we can say 2 things.Q_mech =c and Q_eng = Q_rad.
In general at steady state:Q_eng = h_rad * A_rad * (T_coolant - T_Amb),
So with the T_stat,Q_eng1 = h_rad1 * A_rad * (T_coolant1 - T_Amb) (14)
Without T_stat,Q_eng2 = h_rad2 * A_rad (T_coolant2 - T_Amb) (15)
Where h_rad2 > h_rad1 So, by assuming that T_coolant2 > T_coolant1, we get
Q_eng2 > Q_eng1. (16)
Using equation, 12, we apply equation 16 and it yields,Q_mech2 (1 / eta2 – 1) – Q_alt2 > Q_mech1 (1 / eta1 – 1) – Q_alt1 (17)
Now this is where it all breaks down for me, I can’t find a single valid assumption that will make the above equation work out. Here are all of the assumptions one can make to make (17) valid:1. 1. Q_alt2 < Q_alt1, (If coolant temps are higher at state 2, then Q_alt2 > Q_alt1)
2. 2. Q_mech2 > Q_mech1 (It takes equal power to push a car down the highway, steady state)
3. 3. eta2 < eta1 (as you said, this is why engineers added thermostats)
I can’t think of any exceptions to these, so let me know if you do and what your thoughts are (mistake somewhere??, those danged subscripts are especially pesky). By assuming that tcoolant2 < tcoolant1 then they all work out. So that has to be the conclusion if the math is correct.
@bryesh
Again, some of the assumptions you are making (or not making) about this complicated system appear to me to not be quite right...
Q_mech2 > Qmech1 could be true. Remember, the engine drives the water pump, too. If you remove the thermostat, it's pumping more water, although against a lower pressure rise. The water pump might be drawing more power, or it might be drawing less power.
eta2 < eta1 could be true. As I asserted above, the coolant is going to suck more heat out of the engine if it's flowing faster. Therefore, the engine becomes more inefficient - more of the heat from the burning gasoline is going into the coolant. Even if T_coolant2 < T_coolant1, that might mean that the temperature of the air going into the engine is lower, meaning higher pumping losses at steady-state part-throttle. Thus, eta2 < eta1. A real gasoline engine is way different than the Otto engine from thermodynamics class.
Q_alt2 < Q_alt1 could be true. If the coolant is sucking more heat out of the engine, then it's also possible that less heat is going into the exhaust, oil, etc.
Any one of the above could be true, which could lead to the result that T_coolant2 > T_coolant1. Please understand that I am not saying that T_coolant2 > T_coolant1 on every vehicle. I am saying, "it depends", specifically on how much Q_mech, eta, and Q_alt change. In some cases, coolant temperature will increase. In other cases, it will decrease. Our members own experiences in this post show this.
Let me ask you a question: Let's say that your math is right, and removing the thermostat will cause the coolant temperature to DECREASE for every engine and radiator combination. What that means is simply this: you have proven that increasing cooling flow rate GUARANTEES that steady-state coolant temperature will decrease, right? If that were the case, why wouldn't engineers design the thermostat to have a 3-inch opening? Why wouldn't engineers design the hoses to be large, smooth, no inner springs, and flow tons of coolant? Why wouldn't engineers design the water jackets to be very smooth and well shaped for flow? Have you ever cut open an engine block or cylinder head and looked at the water jackets - they are terrible for promoting flow. Why wouldn't engineers design the head gaskets to have huge holes to allow lots of coolant to flow through them? Helk, if increasing coolant flow guarantees lower coolant temperature at steady state, then let's make everything in the cooling system flow well! If we do a good enough job, then we can decrease the size of the radiator to the size of a heater core! Man, the styling department would love that! So, why don't engineers make any effort to improve coolant flow through the engine? Why do they use small thermostats that don't flow very well when open? If simple equations proved that increasing cooling flow guarantees lower steady-state coolant temps., then engineers would already have been all over it, yes? And yet they don't seem to care... why?
Mike
Again, some of the assumptions you are making (or not making) about this complicated system appear to me to not be quite right...
Q_mech2 > Qmech1 could be true. Remember, the engine drives the water pump, too. If you remove the thermostat, it's pumping more water, although against a lower pressure rise. The water pump might be drawing more power, or it might be drawing less power.
eta2 < eta1 could be true. As I asserted above, the coolant is going to suck more heat out of the engine if it's flowing faster. Therefore, the engine becomes more inefficient - more of the heat from the burning gasoline is going into the coolant. Even if T_coolant2 < T_coolant1, that might mean that the temperature of the air going into the engine is lower, meaning higher pumping losses at steady-state part-throttle. Thus, eta2 < eta1. A real gasoline engine is way different than the Otto engine from thermodynamics class.
Q_alt2 < Q_alt1 could be true. If the coolant is sucking more heat out of the engine, then it's also possible that less heat is going into the exhaust, oil, etc.
Any one of the above could be true, which could lead to the result that T_coolant2 > T_coolant1. Please understand that I am not saying that T_coolant2 > T_coolant1 on every vehicle. I am saying, "it depends", specifically on how much Q_mech, eta, and Q_alt change. In some cases, coolant temperature will increase. In other cases, it will decrease. Our members own experiences in this post show this.
Let me ask you a question: Let's say that your math is right, and removing the thermostat will cause the coolant temperature to DECREASE for every engine and radiator combination. What that means is simply this: you have proven that increasing cooling flow rate GUARANTEES that steady-state coolant temperature will decrease, right? If that were the case, why wouldn't engineers design the thermostat to have a 3-inch opening? Why wouldn't engineers design the hoses to be large, smooth, no inner springs, and flow tons of coolant? Why wouldn't engineers design the water jackets to be very smooth and well shaped for flow? Have you ever cut open an engine block or cylinder head and looked at the water jackets - they are terrible for promoting flow. Why wouldn't engineers design the head gaskets to have huge holes to allow lots of coolant to flow through them? Helk, if increasing coolant flow guarantees lower coolant temperature at steady state, then let's make everything in the cooling system flow well! If we do a good enough job, then we can decrease the size of the radiator to the size of a heater core! Man, the styling department would love that! So, why don't engineers make any effort to improve coolant flow through the engine? Why do they use small thermostats that don't flow very well when open? If simple equations proved that increasing cooling flow guarantees lower steady-state coolant temps., then engineers would already have been all over it, yes? And yet they don't seem to care... why?
Mike
Because the goal of the cooling system isn't to make the engine as cool as possible. It's to hold it at a certain temp for cleanest emissions throughout the warranty period. Typically the engineers never start with a clean sheet, they have to use parts/engines out of the parts bin that will do the job. Once the GN could maintain a temp in stock form their job was done. And most of the job was done with existing parts from the GN inventory.
We're the ones that like seeing just how far we can stress the parts.
On the "Why wouldn't engineers design the head gaskets to have huge holes to allow lots of coolant to flow through them?" question, they kinda do. Find a thread on BBC "series .VS parallel cooling". You'll see they changed over to a parallel cooling system by increasing the head gasket holes to even out the combustion chamber/water temps. (I adapted a little of that stuff when I build my 4.1 to try and get the chamber cooling a little more consistent)
We're the ones that like seeing just how far we can stress the parts.
On the "Why wouldn't engineers design the head gaskets to have huge holes to allow lots of coolant to flow through them?" question, they kinda do. Find a thread on BBC "series .VS parallel cooling". You'll see they changed over to a parallel cooling system by increasing the head gasket holes to even out the combustion chamber/water temps. (I adapted a little of that stuff when I build my 4.1 to try and get the chamber cooling a little more consistent)
Somewhat true. In the case of the LC2, you are probably correct - they were working with a given block, heads, and cooling system. Once they determined that they kept the cooling temperature where they wanted it, they said "good enough", most likely. Although it's interesting that they felt the need to add an oil cooler...
I was working for one of the big three back in the 90's. We developed a new V8 engine completely from scratch - it was the first engine that company made that used an inlet thermostat. That V8 was used in vehicles that had to tow, so cooling system performance was important - you need a lot of cooling to tow a large heavy trailer up a long steep hill in the desert, which was one of our benchmarks. Since we were developing a brand-new engine with a brand-new thermostat design, we had our chance to make the thermostat as big as we wanted. It wasn't an "off the shelf" thing. And yet, that thermostat was designed with an opening that's about the same size as other modern thermostats. We didn't make any attempts to increase cooling system flow by making the thermostat huge or anything like that, even though we had the opportunity.
Interesting side note to that engine - several years later, we decided to make a "HO" version. We increased power by about 15%. When we completed the first durability tests, we could see the obvious flaw in our head gasket design: the front two pistons were still aluminum color, and they got progressively darker until the rear two pistons, which were almost black. I was responsible for solving this problem, since I was the engineer responsible for the block and heads on this new HO engine. We did some flow studies (CFD and windowed engine) and learned that even at high RPM's, the speed of the coolant traveling through the rear of the block was very poor. The holes in the head gasket near the front were too large on our parallel flow system, and the coolant velocity at the rear of the block was very slow. Slow velocity = low "h" heat transfer coefficient. We solved the problem by changing the size of the holes in the head gasket to make the system more like a series cooling system and less like a parallel system. We did NOT increase the size of the thermostat, remove the thermostat, or anything that increased the overall flow. We simply changed the size of the holes in the head gasket to force more of the coolant to the rear of the block.
The coolant flow through the engine only has to be high enough to get circulation at idle and ensure decent coolant velocity at all parts of the engine block/heads at high RPM and power (make sure there is a good "h" in all parts of the water jackets). Further increases in coolant volume don't necessarily improve steady state temperatures, even when pulling a trailer, as I've said above.
-Mike
I was working for one of the big three back in the 90's. We developed a new V8 engine completely from scratch - it was the first engine that company made that used an inlet thermostat. That V8 was used in vehicles that had to tow, so cooling system performance was important - you need a lot of cooling to tow a large heavy trailer up a long steep hill in the desert, which was one of our benchmarks. Since we were developing a brand-new engine with a brand-new thermostat design, we had our chance to make the thermostat as big as we wanted. It wasn't an "off the shelf" thing. And yet, that thermostat was designed with an opening that's about the same size as other modern thermostats. We didn't make any attempts to increase cooling system flow by making the thermostat huge or anything like that, even though we had the opportunity.
Interesting side note to that engine - several years later, we decided to make a "HO" version. We increased power by about 15%. When we completed the first durability tests, we could see the obvious flaw in our head gasket design: the front two pistons were still aluminum color, and they got progressively darker until the rear two pistons, which were almost black. I was responsible for solving this problem, since I was the engineer responsible for the block and heads on this new HO engine. We did some flow studies (CFD and windowed engine) and learned that even at high RPM's, the speed of the coolant traveling through the rear of the block was very poor. The holes in the head gasket near the front were too large on our parallel flow system, and the coolant velocity at the rear of the block was very slow. Slow velocity = low "h" heat transfer coefficient. We solved the problem by changing the size of the holes in the head gasket to make the system more like a series cooling system and less like a parallel system. We did NOT increase the size of the thermostat, remove the thermostat, or anything that increased the overall flow. We simply changed the size of the holes in the head gasket to force more of the coolant to the rear of the block.
The coolant flow through the engine only has to be high enough to get circulation at idle and ensure decent coolant velocity at all parts of the engine block/heads at high RPM and power (make sure there is a good "h" in all parts of the water jackets). Further increases in coolant volume don't necessarily improve steady state temperatures, even when pulling a trailer, as I've said above.
-Mike
@mgmshar
Thanks again for you post.
I have to say that I misinterpreted one of your statements before. I have held to the concept in my head that engine efficiency can't decrease with increasing coolant temperatures and I interpreted one of your posts as aggreeing to this concept, but I can see now that it is simply a bad assumption in some cases as you have tried to explain to me.
I must admit that I was not understanding some fundamentals of an internal combustion engine, and while I think I have rectified it now in my head, I'll try to put it to paper when I get some time to see what you think. I think now it will show what you have been saying all along.
I'll try to see if I can put something together tonight, but it might not happen for awhile.
Thanks again for you post.
I have to say that I misinterpreted one of your statements before. I have held to the concept in my head that engine efficiency can't decrease with increasing coolant temperatures and I interpreted one of your posts as aggreeing to this concept, but I can see now that it is simply a bad assumption in some cases as you have tried to explain to me.
I must admit that I was not understanding some fundamentals of an internal combustion engine, and while I think I have rectified it now in my head, I'll try to put it to paper when I get some time to see what you think. I think now it will show what you have been saying all along.
I'll try to see if I can put something together tonight, but it might not happen for awhile.
Basically, heat in the engine pushes the piston down. The 4stroke otto cycle engine is VERY inefficient. Lets say 1/3 of the BTUs of the gas push the piston down, 1/3 heats the exhaust, and 1/3 heat the water jacket. The more you can skew the available BTU's to the piston and away from the other two, the better it is.
For the factory, they like to run them hot for emissions laws and gas mileage. They also have to account for having cars with warranties getting fueled at every gas station in 'Merica by every demographic of drivers. Since they have to work around that stuff, they have to leave a buffer for every semi-reasonable scenario.....
Then you have jeaniouses like us... We're generally picky about gas stations, run the highest octane we can find, lower the water temp, sometimes add alcohol or race fuel, then take the wastegate and maxxx out every iota of the octane rating by jacking up the cylinder pressure as far as we can.
On a side note, my 4.3 blazer went from 25MPGs to 20MPGs just from replacing the 195 thermostat with a 180. Needless to say the 195 is going back in.
For the factory, they like to run them hot for emissions laws and gas mileage. They also have to account for having cars with warranties getting fueled at every gas station in 'Merica by every demographic of drivers. Since they have to work around that stuff, they have to leave a buffer for every semi-reasonable scenario.....
Then you have jeaniouses like us... We're generally picky about gas stations, run the highest octane we can find, lower the water temp, sometimes add alcohol or race fuel, then take the wastegate and maxxx out every iota of the octane rating by jacking up the cylinder pressure as far as we can.
On a side note, my 4.3 blazer went from 25MPGs to 20MPGs just from replacing the 195 thermostat with a 180. Needless to say the 195 is going back in.
I think as I mentioned above that I believe I was fundamentally flawed in assuming that efficiency won't change as coolant flow increases. So the math doesn't eliminate the possibility of coolant temps increasing when the thermostat is removed.
So it looks like, as mike has suggested all along, in theory we cannot say for sure what coolant temps will do when removing a thermostat. If increasing the flow causes the engine to become more inefficient, or pull more thermal energy into the cooling system, and these effects are greater than the increase in output of the radiator, then the coolant temps will indeed increase in theory.
@mgmshar
Thanks for all of your input and sharing your experiences with us. It is always good to learn from someone who has experienced more than just turning wrenches or pages in a thermo book!
To answer your question about the size of the radiator; the way I understand it is that radiators have to be a certain size to work because there's only a finite amount of airflow at the front of a car. So there is a limit to how much coolant temps will drop even if coolant flow rates become infinite. If airflow rates were infinite, then the designers and accountants would be orgasmic! Because airflow is finite you need a large radiator.
Now I have a question for you, because I am obviously still struggling with these concepts! Doesn't every thermostat close when the engine is cool and open once it is warm to keep coolant temps from increasing? So if we had one of these motors (theoretically possible!) that "sucked more heat out of the engine" than was "sucked out of the radiator" when coolant flow increased, then wouldn't a traditional thermostat be counterproductive? It seems like it would need to work in reverse, open when below operating temps then close off when hot? Since we have a traditional thermostat can't we assume that increasing flow will affect radiator output more than engine input?
Is there some way that removing a thermostat could cause an engine to suck heat differently than when it was in place? What am I missing now because I am struggling?
Isn't the fact that water pumps are run off the crank another good indication that flow increases increase out the radiator more than into the engine?
Thanks as always,
Bryesh
So it looks like, as mike has suggested all along, in theory we cannot say for sure what coolant temps will do when removing a thermostat. If increasing the flow causes the engine to become more inefficient, or pull more thermal energy into the cooling system, and these effects are greater than the increase in output of the radiator, then the coolant temps will indeed increase in theory.
@mgmshar
Thanks for all of your input and sharing your experiences with us. It is always good to learn from someone who has experienced more than just turning wrenches or pages in a thermo book!
To answer your question about the size of the radiator; the way I understand it is that radiators have to be a certain size to work because there's only a finite amount of airflow at the front of a car. So there is a limit to how much coolant temps will drop even if coolant flow rates become infinite. If airflow rates were infinite, then the designers and accountants would be orgasmic! Because airflow is finite you need a large radiator.
Now I have a question for you, because I am obviously still struggling with these concepts! Doesn't every thermostat close when the engine is cool and open once it is warm to keep coolant temps from increasing? So if we had one of these motors (theoretically possible!) that "sucked more heat out of the engine" than was "sucked out of the radiator" when coolant flow increased, then wouldn't a traditional thermostat be counterproductive? It seems like it would need to work in reverse, open when below operating temps then close off when hot? Since we have a traditional thermostat can't we assume that increasing flow will affect radiator output more than engine input?
Is there some way that removing a thermostat could cause an engine to suck heat differently than when it was in place? What am I missing now because I am struggling?
Isn't the fact that water pumps are run off the crank another good indication that flow increases increase out the radiator more than into the engine?
Thanks as always,
Bryesh
When the engine is cold the thermostat is closed and there is a small bypass hose on the back of the water pump to keep coolant moving. If it were left stagnant you'd have localized boiling (and the expansion that comes with it) starting around the exhaust port in the head.
As the engine comes up to temp, the thermostat will open slowly until it finds a 'happy place' (technical engineering term) to balance flow .vs heat. Keep in mind that the engine temp at the thermostat is only true at the thermostat. The slower the coolant travels the greater the delta between going in the engine and coming out of the engine.
It seems from your typing you're under the impression that the thermostat holds all the keys for flow. That's not true. There are other places in the coolant circuit to offer pressure drop. That's why I suspect that Turbo Nasty has an extremely high flowing radiator that caused an anomaly in his cooling system.
Keep in mind that even though the pump is relative to crank speed, it's not a positive displacement pump. Other factors going on inside there are total system pressure coupled with pressures from velocity and areas of pressure drop like head gasket ports and radiator flues. There's instances where factors can change during use and we don't know it without looking.
As the engine comes up to temp, the thermostat will open slowly until it finds a 'happy place' (technical engineering term) to balance flow .vs heat. Keep in mind that the engine temp at the thermostat is only true at the thermostat. The slower the coolant travels the greater the delta between going in the engine and coming out of the engine.
It seems from your typing you're under the impression that the thermostat holds all the keys for flow. That's not true. There are other places in the coolant circuit to offer pressure drop. That's why I suspect that Turbo Nasty has an extremely high flowing radiator that caused an anomaly in his cooling system.
Keep in mind that even though the pump is relative to crank speed, it's not a positive displacement pump. Other factors going on inside there are total system pressure coupled with pressures from velocity and areas of pressure drop like head gasket ports and radiator flues. There's instances where factors can change during use and we don't know it without looking.
