George G

A friend has the 3 liter V6 on a 1989 1 ton chassis. She felt that it wasn't running right after heating up on the road and took it to a mechanic. He said that number three cylinder compression was only 55 psi. I verified that with my tester. He said that this was typical of this engine. I always thought that these were bullet proof.

The engine does not blow smoke, use oil or backfire and runs fairly smooth. There's no oil or water in the oil or radiator so I figure the head gasket is okay. This was not one of those that was subject to the head gasket recall. I could not hear anything bad with my stethoscope. I was going to flush the engine in case of a sticky valve but it looks clean under the valve cover.

Any guess as to the problem and is there a problem with these motors? Valves , rings or?

Thanks

UncleBob

What's the problem?

Corbit

Head gasket is the most problematic of these motors. 55psi is low . I would check to see if there are bubbles in the water , there is a tester out that can smell exhaust fumes in the water.

eric-the-red

55psi isnt normal. Do a leak down test on #3, that'll tell you where the leak is.

WillRadford

How many miles on the engine? I'd bet the you need a valve job.

91TPU

leakdown all 6 cylinders...so if you have to take it apart, you can fix it all at once!

faubrunner64

Burnd valve gaureanteed, theses engines will burn valves if they are not properl;y adjusted every like 60k miles or so so im betting thats what it is, you will have to remove the head and get it rebuilt and new valves. how many miles are on it?

YotaJunky

Agreed. If there is a significant difference in compression between adjacent cylinders, it could possibly lead to HG failure. A leak down test would certainly give you a better idea of where you are losing pressure (valves, rings, HG).

Troy

George G

67,000 miles on engine. We are trying to determine why the compression is low on that cylinder.

I read something interesting on this engine. It said that the piston ring material is not the best and if the engine over heats the warped piston ring will not go back to seal properly. The previous owner had to replace the water pump. Cause and effect? All other cylinders have up to spec compression.

You people have given some good ideas for diagnosing the problem. The leak down test is a really great idea.

EUROJulian

Dude stop trying to determine... Just inject some motor oil into cylinder in question and check how this will afect compression.
In short: No change, valves. Change, pistons.