# 2004 GMC Duramax 6.6 Heat Loss/Pressure in Overflow



## BCSCOTT3 (Nov 4, 2008)

2004 GMC 2500 Duramax 6.6 Diesel changed 2 thermostats, Heat gets real hot than blows cold, low coolant light comes on. pressure builds up in overflow tank. Cap will blow off it not let out slowly. Is this a head gasket or any other ideas


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## brad96z28 (Aug 21, 2005)

BCSCOTT3;624071 said:


> 2004 GMC 2500 Duramax 6.6 Diesel changed 2 thermostats, Heat gets real hot than blows cold, low coolant light comes on. pressure builds up in overflow tank. Cap will blow off it not let out slowly. Is this a head gasket or any other ideas


It could be or the system could have air in it. Has it been serviced recently drained maybe?


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## MuskokaDon (Nov 28, 2007)

I'd say air-lock or rad cap, you'd know if it was a head gasket


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## BCSCOTT3 (Nov 4, 2008)

AIR LOCK?Whats that and possibly the rad cap


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## MuskokaDon (Nov 28, 2007)

Could be many things... 
is it blowing any smoke?
if you refill the bottle does it empty out again?
remove your radiator cap from the jug and start the truck. If coolant flows back out the cap it could be the EGR cooler, it has ruptured internally and coolant is going out the exhaust. The pressure from the exhaust is pushing the coolant back out the rupture and out of the reserve bottle


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## MuskokaDon (Nov 28, 2007)

try here http://www.duramaxforum.com/ these guys know it all


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## got-h2o (Sep 26, 2008)

MuskokaDon;624099 said:


> I'd say air-lock or rad cap, you'd know if it was a head gasket


Those are symptoms of a head gasket. What else would he know?

Did this only happen after changing the thermostats? If so, probably air lock. If before, it's quite possibly HGs. Miles? LB7 or LLY? A bad rad cap would cause your top hose to collapse, hg's usually make it build pressure. Bad injector cup sleeves will allow it to blow by through the exhaust.


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