Engine Running warm

[03GMCYukonXL]

So my 2004 Tahoe had a small coolant leak where you had to top if off every few weeks. Well it got a bit low and my wife was driving it and it over heated. We let it cool off and added more coolant and the truck did just as good as ever for about a month and I noticed that the leak had gotten worse. I found that, the hose coming straight from the water pump was leaking as well as the weep hole in the water pump.

So.... the water pump and thermostat has ben replaces as well as the hose going to the heater core. The engine runs perfectly fine just a tiny tick below the half way mark on the temp. Then after about 8 to 10 miles, the temp will rise to almost the 3/4 mark. I don't think it's the radiator because the top and bottom hoses are very hot to the touch. I'll admit that the top hose is just a bit hotter. But the thing is, the coolant in the reservoir don't seem to go down any at all but if I unscrew the lid it will boil up. So it is obviously under pressure. Could this be a head gasket issue? I can't imagine what else it could be considering all that has been replaced. It never goes beyond the 3/4 mark but then again I never leave it running under load long enough to find out.

 

[Fless]

You can use a combustion gas test kit, available at most auto parts stores, Amazon, etc.

 

[rockola1971]

Jack the front end up OR Park it facing up hill and let it idle with reservoir cap off for about 30-45mins. You may have air trapped in the block.

 

[03GMCYukonXL]

**Update**

So this project was put on the back burner due to life issues, moving, ect.

So now that the weather is cooler, I fired the truck up and ran down the road a few times going up and down hills. I live in east TN so there are ridge inclines that last up to a mile. Anyway, it was around 55 degrees outside and the coolant temp would barely get above the quarter mark. The attached pic is after about 15 minutes of idling and 6 miles of pedal to the medal driving UP hills. The next morning I drove it to work in about 42 degrees. Same issue. Drove it to get lunch in about 55 degrees. Same. Never above what is in the attachment.

Then, I drive it home, it is about 65 degrees outside. It's a 14 mile trip. On about mile 8, it finally gets up to the halfway mark. By the time I pull in my driveway, (after about 2 miles of up hill), the temp gauge goes above halfway, but not quite the 3/4 mark. I let it sit and idle after pulling in for about 10 minutes and the temp moved back DOWN to the halfway mark......

I'm so confused but I have been told that a stuck open thermostat can cause this issue. I just replaced the water pump and thermostat with whatever brand Autozone sells. I understand that it could've been a bad thermostat from the factory.

The truck runs great otherwise. It may could be a bad coolant temp sensor? The truck did over heat last summer when it got low on coolant.

One last thing to note, I did get a P0420 code for the cats but I KNOW that is BS because I literally just replaced the cats. They both have less than 100 miles on them. They're brand new. According to some research, a stuck open thermostat can also cause this code to pop up. So....I'm leaning towards replacing the thermostat again.

 

[Fless]

Did you get the air out of the system?

It was running hot but now it's running cold? Any recent work with a radiator replacement?

What temp does a scanner read (engine coolant temp) when it's as warm as it gets?

 

[03GMCYukonXL]

Did you get the air out of the system?

It was running hot but now it's running cold? Any recent work with a radiator replacement?

What temp does a scanner read (engine coolant temp) when it's as warm as it gets?

I parked the car uphill and let it idle for 45 minutes with the cap off. The radiator was replaced years and years ago. It had no issues. And it runs cold when it's cool out (less than 60 degree) but will eventually get a bit hot when it's 65 or warmer out. It depends on the outside weather.