Carbon deposit on exhaust push-rod

[JustMax]

Hello,

I'm in process of replacing my OEM LIMG for a Dorman ''problem solver'' one. Now that my LIM is removed, I got a question for you guys. One of my push-rods was full of carbon, and also was the ''rail/sleeve'' where the push-rod goes. The others push-rods and ''rails/sleeves'' are clean. The rocker where that specific push-rod is seems also to be darker than the others.

Here a picture, with a clean exhaust push-rod ''rail/sleeve'' on it's side.



It's a 3100 LG8 in a Chevy Malibu LS '02. Since I own the car, I had problems with random misfires, but only at idle. Spark plugs are good except one (the one with the push-rod problem seems to be wet). Wires are new ones. No C.E.L.

Do you have any idea of what could do that? Exhaust valve guide? An intake port leak on the LIMG?

[geoffinbc]

Thats your coolant leak causing gunk to build up. Looks like it is new. Clean all the parts and reinstall.

[JustMax]

Are you sure a coolant leak would cause that? It's clearly chunks of carbon that I remove, not a mixture of water+oil...

And besides that, my LIMG was leaking outside the engine, on the tranny side/front head. The cylinder affected by carbon deposits is the one completely opposite to the external leak (Acc. belt side/rear head)...

But I don't know, maybe I had another leak inside the engine. (my coolant was always green btw, I decided to change my LIMG because I was adding a gallon per month...)

[Schmieder]

I heard a cylinder running too hot can cause oil to break down and build up. Coking I think it is called.

I would consider investigating the fuel injectors for good spray pattern and make sure there are no vacuum leaks along the runners path. Or anything that would cause excessive heating. I notice these deposits occured by the hot side of my engine when I first started to rebuild it.

Running a cylinder lean can cause oil break down. Not sure but check to see if your oil passages in the pushrods are plugged up. Maybe your rockers are oil starved and heating up from friction.

The engine may have been overheating, that is my first impression.

The cylinder affected by carbon deposits is the one completely opposite to the external leak (Acc. belt side/rear head)...

Check for a vacuum leak at the accessory port on the plenum.

[JustMax]

Well, that's interesting... This engine seems to run hot since I own the car (always 5/8 on the temp. gauge when the engine is hot), It never got over that point (but, maybe it have overheated when it was in the last owner hands..)

6 re-manufactured and cleaned fuel injectors from CS Performance will be swap in that engine (I'm waiting these to close the engine and start it). My old ones were dirty and I was also thinking that was part of my idle problem... I'll check my accessory port on the plenum, I didn't think of it before, but I just remember that the rubber boot on the port was old and cracked, I'll change that too.

Thank you very much for your advices.

[trotterlg]

Just another coolant leak you didn't know you had. Clean it all up and move on. Larry

[Wallace]

Isn't that the drain path for the engine oil back to the pan from the cylinder head? Deposits there would be normal if oil not changed regularly or engine ran hot.

[Schmieder]

Like trotterlg said, it probably is another leak. I trust his opinion.

But the over heating thing, that can be more damaging then you realize. Your Engine coolant temp sensor is right next to the T-Stat. If your T-Stat is failing open or there is another pressure loss in the cooling system, like a gasket leak, the boiling point is lowered. This is why it is bad to open the radiator when hot, because it drops the pressure and ALL the coolant instantly boils. The coolants boiling point temp raises as pressure rises. SO naturally a leak in the cooling system lowers the boiling point.

At the cylinder walls in the cooling passages in the cylinder heads is where it is the hottest, obviously lol. If the boiling point is reached it will flash steam and create a steam wall around the chamber making cooling much harder. It also creates steam pockets at the top of the cylinder heads. the steam pockets do not circulate and heat builds up. So the top of your cylinder heads get REALLY hot and coke any oil that comes in contact with the metal near by. That can clog up the pushrods and start starving the rockers of oil, making more friction which is yet more heat. The engine coolant temp sensor will not register the steam pockets because it is out of circulation. If the situation gets out of control then the steam pocket grows larger until it over comes the coolant flow. By then the ECT sensor will register the extreme heat but it is usually too late by then, the head gasket is cooked.

If the previous owner over heated the head gasket, or if you over heated the head gasket (going into the red) then prepare for a head gasket change in the near future. You may have a head gasket leak now.

Is your exhaust steaming after the engine is fully warmed up? Cars steam when cold at times and is perfectly normal. If you aren't sure, hold a piece of dry paper 1" from the exhaust tip for 10-20 seconds. If it gets wet/damp then you have coolant leaking into the chamber. A Head gasket leak. Does your coolant smell like exhaust? When the car is cold, open the radiator cap and start the engine. Give it mild revs and watch the coolant, is it bubbling any? If so then combustion gasses are entering the coolant. A head gasket issue is fixable if caught early.

And as long as the coolant system can not hold proper pressure you are risking severe over heating w/o even knowing it.

[Schmieder]

6 re-manufactured and cleaned fuel injectors from CS Performance will be swap in that engine (I'm waiting these to close the engine and start it). My old ones were dirty and I was also thinking that was part of my idle problem....

When a car over heats and is shut down, the heat soak is much more intense and that causes the fuel injectors to get much hotter. The fuel in the injectors varnishes from the excessive heat and will reduce the life of the fuel injector.

Cooling issues are the worst as they cause ALL sorts of trouble if left unchecked and allowed to continue over the years.