Low Compression on Cylinder #3

[Michael Camara]

Hey all, new to the forum. Looking for information on a 2005 Limited 210-hp, 3.7-liter V-6.

This car has 36,000 miles on it, one owner dealer maintained. Got a check engine light indicating no ignition on cylinder #3. Dealer changed plugs and coil, thinking it was an ignition problem. 3 months later same check engine light code. Dealer says low compression in cylinder #3 and thinks it's a cracked head.

This is my mother in-laws car, like new, never been overheated. Very low miles, she's elderly.

What does everyone think? Seems unusual to me. Is this a common failure?

Any info would be greatly appreciated.

Thanks in advance.

 

[LibertyTC]

Welcome to the forum.
Loss of compression #3, could be dropped rocker or valve seat/stem seal, remove valve cover. The head should be inspected first at #3 & then possibly re-built.
Cracked head? That is jumping to conclusions if you ask me.

 

[mrlavalamp]

pretty hard to narrow it down to a cracked head with it still on the vehicle. Also, they usually have very severe symptoms, like leaking oil/coolant FAST when hot or even burning one or both of those (smoke out the exhaust for sure).

My experience is that most of the time heads warp before they crack. Doesn't mean that it cannot crack, but usually to tell if that is actually the problem you have to take the head off and bring it in to automotive machine shop with a bench that can pressure test heads.

If the head is cracked then your only option is to replace that casting.

Dealer says LOW compression but that does not mean NO compression. Leakdown testing is in order and when you perform this test you should be able pressurize that cylinder with compressed air and if it is leaking you should be able to hear/see it. Pull the intake off the throttle body, open the butterfly while doing this test, and if it is leaking into the intake side you should be able to hear it, and same at the tail pipe (i usually break the exhaust at the first flange after the header).

With only 36k on it, this shouldn't be rings or anything wear related, but cannot rule them out with so much age on the vehicle (dry starts are hell on engines, and if it sat for weeks at a time, you are getting a VERY dry start, this was exactly the case with a 5.9 durango my ex-MIL had, did rings and bearings on the engine and she was good as new).

 

[Michael Camara]

pretty hard to narrow it down to a cracked head with it still on the vehicle. Also, they usually have very severe symptoms, like leaking oil/coolant FAST when hot or even burning one or both of those (smoke out the exhaust for sure).

My experience is that most of the time heads warp before they crack. Doesn't mean that it cannot crack, but usually to tell if that is actually the problem you have to take the head off and bring it in to automotive machine shop with a bench that can pressure test heads.

If the head is cracked then your only option is to replace that casting.

Dealer says LOW compression but that does not mean NO compression. Leakdown testing is in order and when you perform this test you should be able pressurize that cylinder with compressed air and if it is leaking you should be able to hear/see it. Pull the intake off the throttle body, open the butterfly while doing this test, and if it is leaking into the intake side you should be able to hear it, and same at the tail pipe (i usually break the exhaust at the first flange after the header).

With only 36k on it, this shouldn't be rings or anything wear related, but cannot rule them out with so much age on the vehicle (dry starts are hell on engines, and if it sat for weeks at a time, you are getting a VERY dry start, this was exactly the case with a 5.9 durango my ex-MIL had, did rings and bearings on the engine and she was good as new).

Thanks for the reply mrlavalamp. I definitely think more investigation is in order. A leak down test is definitely the next step. I'd like to hope that with such low miles that it might be something like a head gasket... There seems to be a lot of talk about the valve seats failing on these as well... we'll see.