Cooling results without Thermostat vs. with
- Thread starter turbo nasty
- Start date
Nasty Wendy
Perverted Lurker
- Joined
- May 24, 2001
Is it possible that
if your radiator is clean fresh and new your temps will go down without a thermostat but if your radiator is partially fouled/plugged that the thermostat would provide the service of keeping coolant in there longer to allow the inefficient radiator a better chance/more time to reduce temps??? Could this be one reason we are seeing results that support both???
if your radiator is clean fresh and new your temps will go down without a thermostat but if your radiator is partially fouled/plugged that the thermostat would provide the service of keeping coolant in there longer to allow the inefficient radiator a better chance/more time to reduce temps??? Could this be one reason we are seeing results that support both???
turbo nasty
Turbo Dojo / MNTR
- Joined
- Jul 19, 2001
My tstat, water pump, radiator and hoses were all new
A clogged radiator will definitely benefit from not running a thermostat around town. On the interstate and the extra pump speed won't allow for more flow over the road and the temp will creep up to it's 'balancing point'.
Question for you, what is the difference between a stock GN IC and a GNX one?
...conduction through the cylinder walls, cylinder heads, etc. weren't mentioned because they don't change when you take out your thermostat. The only thing that changes is the convection heat transfer between the liquid stuff (coolant) and metal stuff (engine block, heads, radiator, etc.). Barring any oddities like boiling in the engine or pump cavitation, the heat transfer between the coolant and metal will increase when you increase the coolant flow rate by removing the thermostat. This means that the coolant will be sucking more heat from the engine parts (block, heads) and delivering more heat to the radiator metal. If the amount of additional heat sucked from the engine metal is more than the amount of additional heat being delivered to the radiator metal, then the steady state coolant temperature will rise. If the opposite is true, then the steady state coolant temperature will go down. It's really that simple.
With all of the sucking and delivering above, there must be an R-rated joke somewhere...
@bryesh: In the radiator, there are three heat-transfers that occur - convection from the coolant to the radiator metal, conduction through the radiator metal, and convection from the radiator metal to the air. By far, the convection from the radiator metal to the air is the highest "resistance" to heat transfer. To give you a number, the heat transfer coefficient between the coolant and metal is about 6 to 20 times the coefficient between the air and metal. Let's say you have a big-ass radiator with a big-ass fan, and your air-to-metal heat-transfer coefficient is pretty good (closer to 1/6th the coolant-to-metal coefficient). Then, increasing the heat transfer coefficient on the coolant side will help the radiator reject a meaningfully higher amount of heat. Now, let's say you have a small radiator, little fan, and a FMIC blocking the air flow - your air-to-metal heat transfer coefficient is pretty poor (closer to 1/20th the coolant-to-metal coefficient). Then, increasing the coolant-to-metal coefficient won't do nearly as much for the overall heat transfer out of the radiator - the resistance to heat transfer on the air side is just too dominant. Like you said, if the air-to-metal heat transfer in the radiator is low enough, then you can pump all the coolant you want, but the increasing coolant-to-metal heat transfer coefficient won't help the radiator reject more heat to the air. (BTW, since that higher coolant flow rate is also sucking more heat out of the engine, this is the most likely case where steady-state coolant temperature will increase). Clear as mud?
Mike
With all of the sucking and delivering above, there must be an R-rated joke somewhere...
@bryesh: In the radiator, there are three heat-transfers that occur - convection from the coolant to the radiator metal, conduction through the radiator metal, and convection from the radiator metal to the air. By far, the convection from the radiator metal to the air is the highest "resistance" to heat transfer. To give you a number, the heat transfer coefficient between the coolant and metal is about 6 to 20 times the coefficient between the air and metal. Let's say you have a big-ass radiator with a big-ass fan, and your air-to-metal heat-transfer coefficient is pretty good (closer to 1/6th the coolant-to-metal coefficient). Then, increasing the heat transfer coefficient on the coolant side will help the radiator reject a meaningfully higher amount of heat. Now, let's say you have a small radiator, little fan, and a FMIC blocking the air flow - your air-to-metal heat transfer coefficient is pretty poor (closer to 1/20th the coolant-to-metal coefficient). Then, increasing the coolant-to-metal coefficient won't do nearly as much for the overall heat transfer out of the radiator - the resistance to heat transfer on the air side is just too dominant. Like you said, if the air-to-metal heat transfer in the radiator is low enough, then you can pump all the coolant you want, but the increasing coolant-to-metal heat transfer coefficient won't help the radiator reject more heat to the air. (BTW, since that higher coolant flow rate is also sucking more heat out of the engine, this is the most likely case where steady-state coolant temperature will increase). Clear as mud?
Mike
It most definitely does, if you look at the formula Q(heat) changes when there is more contact time with the water or less. So wouldn't Q(flow) affect Q(heat)?
turbo nasty
Turbo Dojo / MNTR
- Joined
- Jul 19, 2001
I think that is " slowing the coolant flow down". That was mentioned by someone...
I'm not going to bang out the same equations that bryesh and I have been exchanging. This has been beaten to death. The cylinder walls are ALWAYS in contact with the coolant, so they are ALWAYS transferring heat to the coolant. There is no “longer or shorter” amount of time the coolant is in contact with the cylinder walls. What matters is the RATE that heat is being transferred to the coolant (i.e. how much heat per unit time, as in "BTU per minute").
There are three things that "resist" heat transfer from the combustion gasses to the coolant: 1) convection from the gases to the cylinder walls, 2) conduction through the cylinder walls, and 3) convection from the cylinder walls to the coolant. Increasing the coolant flow rate only affects #3. Barring oddities like boiling or cavitation, increasing coolant flow rate will reduce the resistance of #3, because the heat transfer coefficient between the walls and coolant will increase. Stated another way, the coolant will have better ability to suck heat out of the cylinder walls when it is moving faster. Thus, Q(heat) PER UNIT TIME (i.e. "BTU per minute") from the engine to the coolant will go up. For the exact same reasons, increasing the coolant flow rate was cause the Q(heat) PER UNIT TIME (i.e. “BTU per minute”) in the radiator to increase. Stated another way, the coolant will have better ability to deliver heat to the radiator.
I’ll repeat what I said earlier, as somebody who knows a little bit about the engineering behind this stuff. Feel free to believe it or not:
1. It is not inherently obvious whether removing your thermostat will result in a lower or higher coolant temperature. "It depends."
2. The engine cooling system was designed to have the restriction of the thermostat in place, so I recommend keeping it.
I'm now going to pour some synthetic oil into my engine and ponder whether or not I should install a BOV...
Mike
There are many factors involved, not denying that. I am totally aware of CCR(convection, conduction, radiation). I have spent over 3 years doing thermodynamic calculations like these. I work with heat exchangers on a daily basis, I've studied and observed nucleate boiling and DNB. There are many factors, too high of a flow can be just as bad as too low of a flow, that is where the design of the system comes in. Scaling in the passages that can cause wick boiling. I can video a water to water heat exchanger and record temps with a pyrometer and show you how when reducing the flow of hot water coming from a boiler(ie. increase contact time) into the heat exchanger I will get cooler water. I've done this many many times! It works!
I mentioned the IC in the GNX because it has more fins than a regular IC. McLaren did that so the air does not pass through too fast, ie. increase contact time.
There are many factors, ambient temp, relative humidity, flow, contact time, area, etc. Hot travels to cold, if your delta T is 1', heat transfer is going to be really slow when compared to a delta T of 100'.
I mentioned the IC in the GNX because it has more fins than a regular IC. McLaren did that so the air does not pass through too fast, ie. increase contact time.
There are many factors, ambient temp, relative humidity, flow, contact time, area, etc. Hot travels to cold, if your delta T is 1', heat transfer is going to be really slow when compared to a delta T of 100'.
Sorry, I don't agree with this at all. The GNX intercooler has more fins to increase the surface area of the IC. As a side benefit, more fins will give the IC more mass, so there will be more thermal inertia to absorb heat from hot charge air under transient (i.e. launch) conditions. More surface area equals more heat transfer, all other factors being equal. Think about it, if you slow the air down, it will get hotter before it exits the IC. The hotter air will absorb less heat, because the delta-T will be lower. Ideally, you want the air to go through the intercooler very quickly so that it remains cool. This will result in the highest possible delta-T throughout the intercooler and the best heat transfer. Ditto for a radiator. (I'm talking incompressible flow here, not air going Mach-0.6 or something, which is realistic for a car.) Using your argument that slowing the cooling fluid down is GOOD - well, everyone should block their radiators and disconnect their fans, right? That would increase the time that the air is in contact with the radiator and intercooler, right?
The only time slowing the fluid down improves heat transfer (in the incompressible range) is when you slow it down enough that a phase change (such as boiling) takes place. As I'm sure you know, turning water into steam sucks a lot of heat out of whatever metal it's touching. That's why slowing down water from a boiler might result in more heat transfer. The coolant in an engine should be far enough below the boiling point that minimal if any boiling occurs anywhere in the circuit. Having said that, in some cases, there might be some boiling going on that skews the results - I've mentioned that caveat in my posts.
One thing is for sure, there are many factors in play. That is why I've said, several times, that it is not obvious that taking your thermostat out of your engine will cause your cooling temperatures to decrease (or increase). "It depends" on many factors.
...and I've got Hoosier 26X9 slicks mounted on my stock GN wheels. That's the largest you can possibly go!
Mike
Wow, this is all interesting. I have to admit that I have thought more about this over the last week than I care to admit.
I think maybe conversation itself cannot resolve anything, so I have made an idealization to demonstrate my thoughts graphically and will put it out there for critique..
This is my viewpoint on heat transfer rates into and out of the cooling system assuming a constant engine speed, engine output and airflow (otherwise noted ) for the case of a thermostat and without. (I have also ghosted in what I believe happens when some other constants change). In the end, I couldn't come up with what I felt was a reasonable scenario, where coolant temps increase with absent tstat without creating a system that would not live happily (as Earl has said) at a partially open thermostat position (Figure 4), but I'll wait to pass judgment after I receive input from those with more expertise than I.
@mgmshar
Glad to hear that maybe I wasn't too far out to lunch with at least some of what was in my previous post. I think I'll need to read that post again to make sure it all sink in. I'm be interested to hear your thoughts on the graphical approach that I have taken below.
Bryesh
I think maybe conversation itself cannot resolve anything, so I have made an idealization to demonstrate my thoughts graphically and will put it out there for critique..
This is my viewpoint on heat transfer rates into and out of the cooling system assuming a constant engine speed, engine output and airflow (otherwise noted ) for the case of a thermostat and without. (I have also ghosted in what I believe happens when some other constants change). In the end, I couldn't come up with what I felt was a reasonable scenario, where coolant temps increase with absent tstat without creating a system that would not live happily (as Earl has said) at a partially open thermostat position (Figure 4), but I'll wait to pass judgment after I receive input from those with more expertise than I.
@mgmshar
Glad to hear that maybe I wasn't too far out to lunch with at least some of what was in my previous post. I think I'll need to read that post again to make sure it all sink in. I'm be interested to hear your thoughts on the graphical approach that I have taken below.
Bryesh
So are you saying that the same amount of air will pass through a rad with 10 fins compared to one with 100 fins? The designs of fins will make a diffence as well.
Okay, now you’re being silly. But if you ever lived up North were it is really cold that is common practice. Put in a 205’F thermostat, completely block the rad and pull the fan. And if you have an all aluminum motor, good luck producing good heat in -50 weather, especially on a windy day!
Actually with some of the low pressure boilers I’ve worked with operating at 12 psi the water temp is pretty close to car coolants. Most of the Engineers coming out of school that design these systems really don’t understand cooling like the ones of years ago. I’ve worked in a few plants where increasing coolant flow caused more problems than reducing the flow, again comes down to design. And that is why I said it comes down to many factors. I was able to keep plants cooling and preventing them from kicking out on high head by doing things some people think makes no difference. On a 40'C day I was able to reduce head pressure by 20psi, something a guy told me was stupid and would never work. Needless to say the facility manager really liked it when I was actually able to do that. Where did I learn some of these techniques? From really smart practical people! Theory and reality are two different things. Calculations will get you close but are not exact.
Good debate, keep cool!
At this point, I'm going to leave this thread. I have tried to explain my understanding of the engineering behind this the best I can. My answer to this question ("It depends") matches other users' experience when they have removed their thermostats (some reported increasing coolant temps, and some reported decreasing coolant temps). When I start getting the "you're just one of those theoretical guys who can't do anything practical" BS, it's time for me to bow out. People who say stuff like that don't know me very well. There's a time and place for practical, and there's a time and place for theoretical. I've managed to do both in my life. Just because I have an engineering degree doesn't mean I can't change my own oil. I've learned a lot from very smart and practical people, too, working in automotive industry for over 15 years. Sometimes I try to pass on that knowledge. Forgive me for trying. Remember, engineers designed the LC2 in the first place, but practical people learned how to make them run 9's. It takes both. I get that, and I don't appreciate it when people crap on either one or the other.
I don't think a single person has changed their initial opinion about this topic, so there's no point in us arguing about it. Take your thermostat out, leave it in, compare your IC to an industrial boiler or a nuclear reactor, whatever works best for you and your car is OK by me. The engineering behind it is irrelevant if it makes you happy, right?
I've decided against the BOV - I would miss the sneezing. And I'm sticking with conventional oil for now. I think my FMIC is better than a SLIC. I love my Power Plate. I'm running 275/50R15's on 15X9 rims with no rubbing.
Back to work. Sorry boss.
Mike
I don't think a single person has changed their initial opinion about this topic, so there's no point in us arguing about it. Take your thermostat out, leave it in, compare your IC to an industrial boiler or a nuclear reactor, whatever works best for you and your car is OK by me. The engineering behind it is irrelevant if it makes you happy, right?
I've decided against the BOV - I would miss the sneezing. And I'm sticking with conventional oil for now. I think my FMIC is better than a SLIC. I love my Power Plate. I'm running 275/50R15's on 15X9 rims with no rubbing.
Back to work. Sorry boss.
Mike
Mike, that comment was not directed at your skills. It is a reflection of the frustration I had to deal with in the last few plants that were designed by Engineers straight out of school. From one Engineer deciding to take Makeup air from a 4th story building right next to a hot air vent, maybe he didn't realize the dense air on ground level would work better. This caused so many problems till finally a co-worker pointed it out to an inspector that wrote the plant up to have it changed.
The comment I made actually was what the firm that comes in and repairs the Engineer's flawed design told me. In the old days he said, the Engineers that designed these flow loops would spend time in the field and learn from experienced Engineers and he would never have to come into a plant and recommission everything to make it work. So, when this guy speaks I listen!
^Well there's the problem. This is the internet and the internet is in 'Merica!! We use 'F(merican) here not 'C(andian) !!
You're apples and oranges!
What the hell is a BTU? It's a KJ! And the specific heat of water is 4.2 KJ/KgK. That being said, if everything was right an increase in coolant flow should cause an increase in cooling. But there are many factors to be considered, too much flow can be just as bad as too little flow.
There is a multi-million dollar Geo Thermal that was installed at one place I worked. It has yet to produce heat in the winter! The CEO was finally admitted they have the most expensive AC unit.
