94 GT 5 speed is overheating intermittently

[Cajun66]

Hey guys and gals. The last couple of summers I've been having some strange water temp issues on really hot days. On cool days, < 85°, it seems ok, but on hot days the temp will climb rapidly and it will get to the point of labor knocking. The AC will cycle as well, but only when the car is running really hot. I've replaced the fan, flushed the radiator, and gone through 3 CCRMs. Nothing has improved my issues.
Any ideas?

 

[95opal]

Do you have the stock lower air deflector intact? Or is it missing?
Hows the water pump?

 

[Cajun66]

All air deflectors are in place. The water pump is questionable....

 

[Daryl]

+1 with 95opal: Water pump. How’s the thermostat?

 

[unterstutzung87]

Do you own a pyrometer? I have used those to diagnose cooling system problems in the past.

 

[Monsterbishi]

My pick would be the thermostat is sticking closed.

 

[badass98svt]

I'd check the stat, 'STAT!

 

[Daryl]

Cajun,
Git er dun??

 

[r1ch999999]

Mine was doing this, the thermostat was installed incorrectly and wasn't opening properly. I replaced it with a 'fail open' version, which might not be the right one for the 5.0, but I've had no issues since.