Excessive pressure in cooling sytem... head gasket, injector cup seal?
 

Hello. I have an 01 LB7 Duramax. I have lately noticed variance in my truck's cooling system reservoir level. It was down a bit so I loosened off the cap. At a certain point of loosness the pressure in the syem was vented, returning the coolant level to a close to normal level yet spitting some coolant out of the overflow. I thought this odd especially when the engine was cold. Tried a new cap, nothing changed. When it is running it runs flawlessly and if the cap is off, you can see that it is bubbling in the reservoir. There is a slight loss of coolant but it's like it is only as much as what goes out the overflow when I remove the cap to vent the system. The temp guage has never gotten real hot and in the winter it does not get anywhere near normal operating temp in warm weather on the gauge. I have added more power to the engine in the last year with no noticeable adverse effects. I have seen other posts on other sites that suggest a head gasket or possibly a leaking injector cup seal. Does anyone have any idea what this might be and have a suggestion as to how to pinpoint the problem? Where could this gas be coming from? Both of those scenarios make sense but are there any other possibilities?
Thanks

I wouldn't think it was an injector cup unless you recently had injectors done. that doesn't mean it's not that, but i would think it was your head gasket first. :humm:

try washing the rad cap in hot soapy water, if that doesnt help, try a new cap ($12 at a dealer) and then if thats not it then its probably Headgaskets especially if the upper rad hose is still hard after sitting over night

Have you done a combustion gas detection on the coolant?

this may or may not work... the best way to know 100% sure that its gaskets is to have each cylinder pressure checked, i would start with Cylinder 2 on the front drivers side, that is the most prone to blowing out, then cylinder 7 on the back passengers side, it is also prone to blowing

If its got a blown hg and its leaking combustion pressure into the cooling system it will show every time there bud. Maybe we should go more in detail and explain to bring each cylinder to the top, get the correct adapters and buy a leak down gauge and pressure test each one to determine if there is a combustion leak. Then pressure test for coolant leaks?

Always start with the easiest tests first lol
My lb7 lost cylinder 1 first

Mine didn't show on a exhaust gas test.... this is why I say this... but it might..

There is a hose connected to the top radiator hose outlet which leads back to the turbo. I am assuming that it carries coolant to cool the turbine side. Is it possible that I have some boost leaking past something in the turbo charger and getting into the cooling system there? Any ideas on this theory?

anything is possible.... but get an exhaust gas in coolant test done(you need diesel specific fluid) and then if it shows nothing get the cylinders pressure tested... My guess is your headgaskets... I was in denial too..:argh:

Diesel specific? Lol every bottle i have ever seen say for gas and diesel engines on the side of it?
I have a Volvo in the shop that ill take a video example of how to use the kit.

the Kit I used was supposed to work for both, didnt work with mine...... there are diesel specific fluids, depending on the kit

we put the fluid up to the exhaust with the truck running, it changed, but did nothing with the air bubbling thru it on the degas bottle, this is why I say that the test is not always definitive, the only SURE way to test is pressure test the cylinders:pca1:

I bought a block test kit from NAPA auto parts it showed the fluid change color on mine just sat the tube with the fluid on top the surge tank let the truck run for alittle. Yeah I have a 01 lb7 just had the head gasket repair done few months ago. Sucks... More than likely the issue.

To clear something up in regards to the Combustion gas tester....
All engines produce one main gas:CO2, Just like you held that tester up to the exhaust (where CO2 Exits lol ) , the blown head gasket would allow compressed gases to enter the cooling system if the leak was from the cooling jackets between the head and block and compression gases would work their way from the combustion chamber to the cooling tank creating excess pressure and the release of exhaust gases from the cooling system. If your cooling system is being pressurized this is the most likely one, consider this, A LB7's minimum compression should be aprox. 2069KPA or 300PSI compared to a vehicle cooling system rated at or around 14PSI. Which is why I'm so Confident if there was a leak between the combustion chambers and cooling system large enough to pressurize the coolant tank above the 14PSI (IIRC) rated cap that there would be combustion gases showing up on this test. There are some reasons for a false negative test. You can still have a blown headgasket and this test not indicate a failure, but most likely the gasket failure was not in the cooling jacket.
1: Failure to drive vehicle at operating temps for atleast 20 min prior to testing.
2: Failure to catch a small amount of color change (any change at all indicates further inspection needed)
3: Not completing enough pumps on the bulb
4: Too much coolant not allowing collection of the gases in the tank. (rare)

With that said, I have a little problem with the concept of multiple test fluids, and not doubting that you've seen them ( I have not), But in theory these test all work the same, By detecting small amounts of combustion gases, primarily CO2. All vehicles produce CO2 and CO2 is the same regardless of the fuel that produces it. It's a by product of combustion therefore combustion engines produce it :tu: So with that said I'm having a hard time understanding why there would be multiple fluids. Hopefully someone will step in thats had some experience with this area.

For those wondering about testing for blown head gaskets with this method.

It's an extremely easy, Inexpensive and fast way to determine if CO2 is entering the cooling system. Note I didnt say a Blown head gasket! This is only to alert a trained tech or mechanical minded vehicle owner to a problem or to lead them in the direction of a customer complaint. This is not a tell all, more diagnostics are still needed to determine the actual cause of the problem. Without further diagnostics theres a good possibility that you would be guessing what was wrong with your vehicle when repairs start instead of knowing what was wrong!

Like i said, the fluid did not work on my cooling system, but a cylinder pressure test DID! cylinder #2(front drivers side) revealed that it would not hold pressure, once the heads were off we found 4 holes had blown the fire rings:tttt:

I agree with the statements in regards to the test methods above the only true way to get a good idea with the problem is to take it in or if have the resources and get a pressure test on the cylinders I did one of the fluid tests for mine but had a pressure test before final action was taken. Also don't consider one of those gasket sealer kits that claim to fix a leak read where guys used it and messed up there sh#t doing so.