Pressure in cooling system - Chevy and GMC Duramax Diesel Forum
04.5-05 LLY Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 8 (permalink) Old 12-25-2012, 10:32 AM Thread Starter
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Pressure in cooling system

My 04.5 LLY is running fine, does not overheat, but even if I let it sit overnight and crank it cold, let it run for about a minute then shut it off, I have to slowly crack open the top on the coolant resevoir slowly. It is building enough pressure just from running a minute that I have to take my time taking the cap off to keep it from blowing the top off and blowing out the coolant from the resevoir.

If I drive it and get it up to running temp it will just start forcing it out of the overflow tube onto the ground. What would cause it to build up this much pressure? Cracked head? Blown head gasket? Causing compression to get into the cooling system and build pressure? That is what my 99 Trans Am did. Thats the only thing I can figure. Any help or suggestions are GREATLY appreciated. Thanks. And Merry CHRISTmas.
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post #2 of 8 (permalink) Old 12-25-2012, 10:35 AM
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Sounds like your head gasket(s) are blown. I'm sure others will chime in too though. Good time to do studs!!!

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post #3 of 8 (permalink) Old 12-25-2012, 11:26 AM
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Originally Posted by BlackBetty06 View Post
Sounds like your head gasket(s) are blown. I'm sure others will chime in too though. Good time to do studs!!!
X 2. If it sits overnight, is the upper radiator hose rock hard in the morning? That's another indication of HG's.

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post #4 of 8 (permalink) Old 12-25-2012, 12:01 PM
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Yup have the same issue it's defiantly the head gaskets.

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post #5 of 8 (permalink) Old 12-25-2012, 12:06 PM
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Join the club, i have pretty much the same problem. will be doing more than a few upgrades while im that deep into the engine

2004.5 LLY
-straight 4" exhaust
-PCV reroute
-Sinister EGRD
-LBZ turbo MP/resonator plug
-EFILive dsp5(IdahoRob)
-4" lift sitting on Toyo open country M/T 35's

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post #6 of 8 (permalink) Old 12-25-2012, 12:08 PM
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It sounds like Head Gaskets. It's not uncommon for a LLY to get a blown gasket. It also might be the radiator cap but I doubt it, because it builds pressure so fast. It should only build pressure from the heat.

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post #7 of 8 (permalink) Old 12-25-2012, 01:20 PM Thread Starter
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How much would I be looking at to replace the gaskets?
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post #8 of 8 (permalink) Old 12-25-2012, 02:10 PM
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book time is about 35 hours of labor. Plus parts--gaskets [$200]and new bolts--[$100] most use studs-[$600]. Should also consider replacing the water pump-- if it is original.

Yes, you have a bad head gasket-- Sorry.

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