cooling system high pressure and losing coolant

[aceme2]

I have a 2002 Chevy Silverado with 6.6 Diesel LB7. Have excess pressure in cooling system , losing coolant, does not over heat. I also had a oil test done for coolant in oil, none found. Tested coolant for exhaust neg results. I am leaning towards headgaskets or a cracked head. Any ideas out there?

[CoyleJR]

If you are loosing coolant in small amounts over time and not over heating I would suggest replacing the coolant pressure cap. They are inexpensive and a good starting place to look for the cause. My 2006, LBZ was using small amounts of coolant for several years and a new pressure cap solved the problem.

Good luck
John

[More Power]

A typical cooling system will reach a pressure of 8-10 psi at operating temperature. After sitting overnight and the engine cools completely, that pressure should drop to near zero. A cooling system that holds significant (a few psi) pressure overnight indicates a problem with combustion pressure finding its way in to the cooling system. Jim

[gary_lucas]

I had something similar for a while. I bought a new cap and I also had a collapsed upper rad hose.

Seemed fine for awhile, then had additional issues.

Eventually (over a couple of years) it lead towards head gasket failure :(

Hopefully yours goes somewhere else!

[chessy56]

Hope you got 'er fixed by now but man, this sounds really familiar. About 2 years back I had the same thing with an '01 LB7 and it turned out to be a leak at the #7 cylinder- bad head gasket. And this, after a new set of head gaskets that were replaced about a year earlier. I took Kennedy's advice and bought a set of studs- no more OEM head bolts. And no further leaks.

[More Power]

... I had the same thing with an '01 LB7 and it turned out to be a leak at the #7 cylinder- bad head gasket....

How many miles did the engine have on it - with head bolts - before the head gasket failed the first time?

[chessy56]

The first time it failed, I had ~338K miles on it. I saw leakage from below around the #1 cylinder. It hadn't totally failed yet, but the evidence was clearly indicating a leak was in the making (it had the original head bolts). The (2nd) leak was at the #7 cylinder and it occurred at ~401K, less than 2 years later. It now sits idle with ~437K miles on it. I had studs installed during the 2nd HG replacement.

[More Power]

The first time it failed, I had ~338K miles on it. I saw leakage from below around the #1 cylinder. It hadn't totally failed yet, but the evidence was clearly indicating a leak was in the making (it had the original head bolts). The (2nd) leak was at the #7 cylinder and it occurred at ~401K, less than 2 years later. It now sits idle with ~437K miles on it. I had studs installed during the 2nd HG replacement.

So, 338K miles on the original head gaskets and original Torque-to-Yield (TTY) head bolts... Sounds like good service to me. Properly prepping the head and block deck surfaces during a head gasket replacement is important to long-term reliability.