Compression test for blown Head Gasket?

[Realspool]

I am afraid that i might have blown a head gasket.If i just do a compression test of the 6 cylinders and they are all within 10% of each other would i still have to do a leak down test as well.For the compression test i have to run the car to normal operating temperature then take all the spark plugs out and disconnect the orange lead wire by the battery? I then would have to crank the engine and give it full throttle right and get the highest reading for each cylinder?. I am new to this possible head gasket problem. Hope someone can help and explain it a little clearer.

 

[MistaScott]

You don't have to run to operating temp to do the compression test but that is the most accurate way to do it. If you blew a HG or burnt a piston, you will know because a cylinder (or two )will have drastically lower compression or 0 compression if you blew it bad. You will need to remove the plugs to put the tester in. (Make sure all plugs are out so the car won't start.) You then have a friend turn the key and turn the engine over eight times or so while you read the psi. You do not need to open the throttle, just turn the key and let it try to start. Most TRs are around 150 or so per cylinder. It is more important that the numbers are similar than the actual number.

The leakdown test is done to determine exactly where you are losing compression and how much. There are plenty of internet sites that tell you how to do one. Basically you send pressurized air into the cylinder and listen for where it comes out.

Another thing you can do is drop some oil into the cylinder (assuming it has little or no compression) through the spark plug hole and retest compression. If the piston rings are bad the oil will cause the cylinder to regain compression.

Also, check for milkshake on your oil dipstick. Then you definitely have a blown HG, but you can still have a blown HG and no milkshake. HTH.

 

[Realspool]

No milk shake in the oil but just a ticking noise and when i hit full throttle it bucks.I have only lately to begin to think it could be the head gasket.I hear a ticking noise and can't tell if it is an exhaust leak or blown head gasket,I have to go out today and buy a compression gauge.The screw in type seems to be the best.Will an exhaust leak lower the compression in a cylinder Thanks guys Ray

 

[blackbuick87]

Most blown HG's dont tick. You would be on 5 cylinders, and either have chocolate milk for coolant, or smoke would be pouring out from the hood because oil would be pouring out the breathers.

Sounds like an exhaust leak. Check the drivers side header for cracks, and check the crossover pipe for leaks. Any pre-turbo leak will cause headaches

 

[Realspool]

Im praying thats what it is because if i use full throttle up to about 40 mph the car doesn/t skip or making a popping type noise.One thing is I only have a in tank pump that is for Maximum 12.0's.My car puts out around 550 HP.Also when cranking the motor it cranks alot slower compared to any other car i have or have started.I just got a brand new negative battery cable to see if this helps.Maybe the battery is not putting out enough volts?.But that ticking noise that started last week is one of many possible things.I have to take it for inspection in 2 weeks and the place where i get it inspected primarily works on Buick Turbo's.Maybe i should wait and let them tell me what it really is.The guy i take it too has the 4th or5th fastest Grand National in the world(Dale Berrel).But he is a good honest guy which is hard to find for a mechanic! thanks for your replys. Ray

 

[MistaScott]

My HG was blown into the valley and the car sounded like a crop duster. I heard a sputter sputter sound and it drove like crap. If you've lost a cylinder you should know it just from how it drives.

The leakdown test can help you figure out if its exhaust or not. Yes, an exhaust leak will cause you to lose compression but usuually not down to 0.

 

[Realspool]

Well im going Monday to a Grand national specialist.This place will be able to tell if it is an exhaust leak or blown head gasket.To me it sounds like exhaust and i can't get the car high enough in the air to feel air to seewhere the leak is. if there is indeed a leak it is an exhaust manifold crack in the front passengers side or turbo to header which I am thinking it very well could be there. Thanks for the reply Ray