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Discussion Starter · #1 ·
I have a 2004 GMC Canyon SLE 5cyl with about 118k miles on it. This week the air conditioner stopped working out of the blue. Then the next small trip I made, it started working fine again. Then I got the “ac off/eng hot” message. It is running hot, too. I could only drive maybe 2 miles with the air maxed out before the gauge hits max and I get the message. I noticed my coolant reservoir was empty so I thought that may be the issue. Filled it up and still had issues. Noticed there was some coolant resting on top of the radiator, so I replaced the radiator. That didn’t change anything so I then moved on to the thermostat, then the water pump. The problem is still exactly the same. I’ve never noticed any leaks. What’s the next step? Could it be simple as a radiator cap? Appreciate the help. This forum helped me through the repairs up to this point.
 

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I agree with OldTime, Check the oil for water as well as I had a head gasket issue that never mixed the oil in the coolant, but there was coolant in the oil.
 

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Discussion Starter · #4 ·
Thanks. I’m not seeing any loss of power or any smoke from the truck, so I was hoping it wasn’t a head gasket issue.
 

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Discussion Starter · #5 ·
None of the coolant looked milky or discolored from when I drained it putting the radiator in.
 

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Pull the oil dipstick and look for signs of coolant in the oil like milky gunk or foamy crud .
 

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Discussion Starter · #8 ·
The oil and coolant seem normal, but I started it and let it idle for a while and it idled very rough. Never noticed it doing that before. I’m afraid it’s a head gasket. On a drive with the AC on Max it overheats within 2 miles consistently. Would a bad sensor cause it to overheat so quickly? Everyone else seemed to have the problem of their gauge not working and not much worse.
 

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Did you replace the radiator cap? That could have gone bad too.
Could also be air in the system.

With a cool engine pull the rad cap off and keep an eye on the temp gauge, as it keeps warmer rev the engine to really get that water pump going, and peek through the hood/windshield and keep an eye on the radiator. As long as it's bubbling keep going, add coolant/distilled water until it's absolutely full and no longer bubbling.
 
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