XLR8BYU

Returning home from Carlisle, had a weird overheating issue develop.
Turned the AC on and was cruising backroads @ 55-60MPH, and the temp slowly creeped up to 245-250. This has happened in the past (Car has Heads/ mid size Cam and always runs a little hotter with AC), but never past 235.
Turned AC off and hit the highway @ 70-80MPH (6th gear 1800-2000 RPM)
Temp kept rising to 250! Slowed down to 60-65 and lowered to 235-240.
Pulled over for 25 minutes to get gas and let it cool. Checked for anything blocking airflow, looked clear.
Back roads the rest of the way home, 5th gear 55-60mph (staying under 2000rpm) and temp stayed @ 220. As soon as I went over 65 (even staying under 2000rpm in 6th gear), it would start to immediately moving up.

Any ideas what this could be? Radiator is 2 years old, and was flushed 1 year ago

runner140*

Make sure your tstat is not stuck....test it.
Make sure you have a good radiator cap...check the pressure.
Re-burp the system. There are several ways...use the way that is best for you. (I bring up to temp...tstat open.... while cap off and engine running and go for a SHORT drive). Then refill up to line.

73Corvette

Our 04 runs about the same temps A/C on or off... you either have a water restriction, thermostat, water pump belt slipping, or air IN your coolant system...
or you aren't getting enough flow thru the A/C condenser/Radiator... I trimmed my middle air dam about 2" and it didn't change temps at higher speeds... 75-80 ish.
I would be probably be leaning towards the stat if it were my car and I would try a 160 degree stat... but, that's a thing that I believe makes a difference that some don't agree with.
It's fairly inexpensive and simple to do... you still MUST not have ANY air in the system for it to work properly...

XLR8BYU

I do have a 160 thermostat that was replaced when I did the radiator 2yrs ago. The car is lowered with a front splitter, but the center air dam is in place and I did the front license plate screen mod to help with airflow as well.

Seeing as how this issue just raised it's head, it may be the therm....

73Corvette

Keep us posted...

0Anthony @ LGMotorsports

Anything blow up under the nose of the car and block the radiator?

Seems odd it gets hotter with speed, which makes me think an air flow blockage.

If the thermostat was stuck it would get hot and never cool off again...or typically if they are stuck shut it just keeps going.

Do you know if both fans are turning on?

73Corvette

I wouldn't think the fan operation at the MPH and temps the OP was describing would make any difference... the temps never got down to 226

73Corvette

NOT sure what that means... My radiator LOOKED clean from every angle and possible way I could check it... even tried blowing it out with a special wand I made to fit between the A/C condenser and the Radiator...nothing. SO, I took my radiator OUT... it was completely blocked... you couldn't see thru it. It was like some kind of little tiny bricks in between the fins... had to soak the radiator with water and rinse it out and gently spray it, several times before I finally got CLEAN .., you could actually SEE thru it.... Your A/C condenser could be the same way...

XLR8BYU

By 'looked clear', I meant I didn't see any trash or objects blocking the front of the radiator.

73Corvette

mmm not a good way to tell if your getting the air flow you need for proper cooling...