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Ok I’m new to this forum but I have a 07 Chevy duramax lbz classic body style. I can be just driving it and it’s random sometimes it does it the day after I add coolant or week later. I can be driving it and stop somewhere and leave the truck running when I left the truck temp was 210, I get back in and it’s sitting on 160. And later it’ll puke coolant. I’ve replaced the thermostats already. I’ve read it could be head-gaskets but I find it hard to believe it could be head gaskets. Could it but something else?
 

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Head gaskets if it's coming out the over flow. IMO

Could be water pump, though
 

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Discussion Starter #3 (Edited)
I’m hoping it’s the pump I just don’t believe it could be a head gasket. I’m new to a duramax. But something else I notice it cold I’ll fill the overflow up and after driving it for a bit it’ll be almost be empty. Why does it suck all that fluid up? There’s no min or max line on the container, I just don’t quite understand why it pulls all the fluid out then manages to push it out. Are the ways to test to see if it’s a head gasket before pulling the heads off? And anyway to check the pump without pulling it off? I appreciate all the input thanks
 

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Take it out tonight and romp on it a little bit. Tomorrow morning, give the upper radiator hose a squeeze. It should be relatively soft, like a tennis ball.

If it's hard... better save for a head gasket job.

I, myself, was once in head gasket denial, too. Lol with my lly
 

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Discussion Starter #7
Got in it’s this morning hose is soft could squeeze it flat drove 5 mins got out let the truck idle for 10 and come out coolant coming out the over flow
 

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How would I temporarily bypass the EGR cooler? And will it hurt anything while I drive it to see it’s that’s the problem
You will need to acquire what's called a 'blocker plate', 'bout $10. Insert the block plate at the flange on the rear of the EGR cooler (search the forum, numerous threads and pics). With the block plate installed, there is now no exhaust gases (pressure) running thru the cooler. Test again with the block plate installed, see if it duplicates pushing coolant out.
 

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You will need to acquire what's called a 'blocker plate', 'bout $10. Insert the block plate at the flange on the rear of the EGR cooler (search the forum, numerous threads and pics). With the block plate installed, there is now no exhaust gases (pressure) running thru the cooler. Test again with the block plate installed, see if it duplicates pushing coolant out.
I am having the same issue. Only blow coolant out of overflow tank while towing. I have the egr blocked with a plate. Been in there for 10 years. I have taken notice that when the ect gets over 208 it blows coolant out. I have changed caps twice now. I checked the upper hose this morning and it was "soft" and easy to squeeze. Not collapsed but trying too. This issue started probably a year ago and has gotten worse. Thoughts? Recommendations?
 

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So did you ever figure this out? You could get a good look at your coolant tank and see if it is turning black at the bottom to see if it's head gaskets.
You could also see coolant dripping off the transmission, oil cooler, or passenger side of the engine. EGR cooler hoses might show a crust layer of coolant built up around the leak areas. I had that on mine. I was also loosing coolant.

I never found it hard to believe head gaskets could be blown. I wanted it to be anything else and always THOUGHT it WAS head gaskets. I plugged every other leak before getting to head gaskets. Any reason you "have a hard time believing it could be head gaskets" would be interesting to know.
 

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Could the egr cooler even though supposedly block still let some exhaust gas into cooling system.
How would an EGR block plate allow exhaust gas into the cooler? Through the valve on the exit towards the front of the engine that has the air intake pushing air towards the turbo?
 
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