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Discussion Starter #1
I found out a couple months ago I head a blown head gasket. The temp gauge never showed signs of overheating. At that time I checked the hoses and the upper hose was hot & the lower was cold when engine at “operating” temp. I thought well thermostat went bad. I replaced head gaskets, water pump, thermostat. I have just come across the same initial situation of the upper hose is hot, lower hose is cold, temp gauge did not show over heating. Both heater core hoses are hot & I have heat. Has anyone ever come across this or ha e an idea of what would cause it.
 

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Verified the coolant level? Is it possible the coolant temperature sensor is reading inaccurately? :unsure:
 

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Discussion Starter #3
I know the overflow tank was full and the radiator. The coolant was flowing properly between the hoses up until I just recently found this repeat issue.
 

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The sensor will only work if it's in water. Verify you don't have air trapped.

Does the gauge start off cold and come up to engine temp?
 
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Probably a mute point, but can view the engine coolant temperature in engineering mode. Pontiac G8 Forum. An engine temp (temperature hot) message is supposed to appear on the instrument cluster when the vehicle overheats. Perchance is the car boosted? Recall reading prolonged excessive pressure or detonation can also cause a blown head gasket.
 

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Having a head gasket fail does not mean you ever over heated the engine. Engine knock can take out head gaskets, piston rings and lands , cranks , rods and bearings. Bad gas, low fuel pressure, clogged injector can all cause this. Where did your gasket fail? Beside a head bolt or between two cylinders?
 

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Discussion Starter #8
Probably a mute point, but can view the engine coolant temperature in engineering mode. Pontiac G8 Forum. An engine temp (temperature hot) message is supposed to appear on the instrument cluster when the vehicle overheats. Perchance is the car boosted? Recall reading prolonged excessive pressure or detonation can also cause a blown head gasket.
It’s not boosted just LTH & CAI with a tune...every time I viewed coolant temp in engineering mode it was around 91-94c.

Having a head gasket fail does not mean you ever over heated the engine. Engine knock can take out head gaskets, piston rings and lands , cranks , rods and bearings. Bad gas, low fuel pressure, clogged injector can all cause this. Where did your gasket fail? Beside a head bolt or between two cylinders?
I had low compression on number 3 cylinder (160psi) others were close to 220psi. Replaced head gasket & all cylinders were within 10-20 psi.
 

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So the shop never showed you the gasket?
 

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Discussion Starter #10 (Edited)
I repaired it myself....couldn’t see any ‘breaks’ in the gasket. It also pealed apart as we removed the cylinder head.

I’ll add this it has a rough idle or almost stalls after startup in the morning mainly when it’s been sitting overnight & the temps are in the 30-40 or colder. If it does stall I am able to start it up and it idles no issue.
 

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A few days ago, it was my turn to have the upper hose disconnect from the radiator due to about 1/4" of the tube breaking off. Shoved the hose back on an replaced the OEM clamp with a SS worm type clamp. After adding lost antifreeze back into the radiator, I ran the engine an after a short period, the coolant in the radiator disappeared. Added more coolant an the level remained good. After the temp ramped up, you could see the water flow into the radiator from the pump. This told me all the air was removed, the thermostat was open, an the pump was circulating the coolant properly.

If you still have a problem, can you see the coolant running into the radiator, once the temp is up to normal. Also maybe the ECT sensor resistance is in error so much that it thinks the engine temp is below freezing (to start with). That would make it "not" agree with the IAT incoming air close enough an could fool the ECM into supplying an incorrect fuel air mixture at first cold startup.
 

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Discussion Starter #12
I remembered that back in March a bunch of CEL tripped I cleared them & they didn’t return than covid came & I was at home for 2 months & didn’t think much of it cause the car sat for that time. Warm weather came and it drove just just fine until I did an oil change & noticed the coolant mixed with it. The picture is the following codes that came up back in March.
182959
 

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Discussion Starter #13
I believe I figured out my issue I replaced the radiator in 4/2019 from O'reillys it had a drip/leak at the elbow connection but I was able to get it to stop at the time. I believe it slowly dripped coolant which didn't allow it to build pressure over time in the system which caused me to leak coolant to the point there wasn't enough in the system to flow but not cause a major leak. That teamed up with spark plugs that were toast after 20k miles which caused the car to go heywire and cause the initial blown head gasket. Well that lead me to renting a coolant pressure tester to help verify the coolant system didn't have a leak or that I didn't have another blown head gasket. Upon pressurizing the cooling system the radiator started to leak from the lower elbow connection. I pulled it and replaced it with a warranty one through Oreily. Installed the replacement and it started to leak from the elbow connection. Are there any good replacement radiators out there? Or are the only decent options OEM or cold case? Did anyone get a good fix for that connection or is it just luck of the draw
 

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Which brand of radiator was purchased from O'Reily's? Have read oem radiators are sometimes hit-n-miss. Cold Case radiators had an issue(s), but believe those were addressed although not 100% sure. Had pretty decent fortune with a brand called OSC (Rock Auto) installed on various vehicles, but never got around to putting one in the G8.
 

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Discussion Starter #16
Which brand of radiator was purchased from O'Reily's? Have read oem radiators are sometimes hit-n-miss. Cold Case radiators had an issue(s), but believe those were addressed although not 100% sure. Had pretty decent fortune with a brand called OSC (Rock Auto) installed on various vehicles, but never got around to putting one in the G8.
The radiator from Oreilly’s was a Murray Heat Transfer.
Yea I saw the OSC brand on rockauto.
thanks
 

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Discussion Starter #18
awesome thanks, I’ll check these out.
 

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Discussion Starter #19
Well I got the radiator in and the outlet pipe wasn’t leaking. Filled with coolant hooked everything back up. Go to start the car & after a minute or 2 the transmission cooler pressure line blows past the clip/lock ring...fantastic. Pushed the line back in made sure it was seated good put the clip back on and was good. Started back up and same thing. So looks like now I have a blockage or restriction in the cooler for the transmission.
 

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Gesh, what an ordeal and what brand is the replacement?
 
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