I've been dealing with this problem for what seems like forever. The past fixes have always been a bad thermostat, leaking radiator, or frozen up water pump.
For the last 4 months it slowly overheats with the a/c on, highway or city, and runs 220-230 without the a/c on, highway or city. Although the non a/c temps may be normal I've owned the car for 14 years and with 160 stat it has never gone over 190. It has sat around a lot as I drove my other car but I tried to start it every once and a while. My only thought is that the bottom half of the radiator may be clogged. This is what I know:

*I've replaced the stat 3 times lately thinking I may have a bad one
*I haven't lost any coolant
*I've replaced the rad cap
*The radiator visually flows adequately
*My old fan worked but I got a Taurus fan for the shroud and improved performance - it works properly - runs constantly with a/c and turns on at correct point without a/c
*No hoses are collapsing
*The a/c is ice cold and the engine runs butter smooth
*I returned the timing from 4 adv back to the stock 0
*The radiator is only a few years old and doesn't have many miles on it
*There is no debris or bent fins on the radiator or condenser
*The coolant mixture is 50/50 or very close
Thank you for your time.

 

Is it literally overheating, or are the temps just higher?

If it's not boiling over, maybe your guage is off (like everyones), or maybe you need a new sender for the guage (driver side head).

 

well if the core of the radiator is cold in some spots you could have a plugged radiator. it probably is a bad gauge. I changed my fan sensor at one point to make it come on sooner and I have never seen my car run hot even with a bad gauge...

 

Well my gauge correctly reads the drop when the stat opens and it's the correct temp when the fan comes on (a/c off) so I assume it is relatively accurate. I turn the a/c off when it gets to the first red portion of the gauge and it will start to drop down to the 220-240 range. I forgot to mention my air dam is also intact.

 

Solved??!! Well for the last week and a half or so it hasn't even come close to overheating. I just got back from Dallas (45 min each way) and it sat at 170-180 both trips. I'll list the changes that have taken place no matter the significance.
-The high temps outside have gone from averaging 105 to averaging 95
-I turned the cycling switch screw clockwise quite a significant amount to make it cycle every once in a while (I never heard, saw or felt it cycle before with this new switch or with the old switch)
-I undertightened the non-vented gas cap that O'Reilly said was the correct part #.
-My oil was about .25 quarts low...damned rear main seal
-I've been listening exclusively to my Forever the Sickest Kids cd
Thoughts?

 

what temp thermo stat are u running?

 

160

 

"cycling switch screw clockwise"

What is that all about? I need to know.

 

If you pull the 2 wire connector off of the cycling switch on the dryer/accumulator there's a flathead adjustment screw inside the switch (The device screwed onto the dryer/accumulator). Clockwise turns make it cycle more counterclockwise turns make it cycle less. Since the cycle switch is for r12 and I've since retrofitted to 134a I supposedly should have had to adjust the screw counterclockwise to make up for the pressure differences between r12 and 134a and make it cycle less but my compressor clutch was engaged all the time with the a/c on so I had the opposite problem. Strange but so far successful.

 

Im gonna call a bad gauge. Get a heat gun and measure temp at the upper hose. Compare.

 

Like I said before I would definitely concede to the bad gauge theory if the gauge hadn't correctly responded to the stat opening around 160, fan turn on temperature at 220 (no a/c, aftermarket fan controller), and the previous drop in temps after I turned the a/c off when it was still overheating with the a/c on. Seems dead on.

 

Definitely the Forever the Sickest Kids cd!

Guess I'm an old fart, 'cause I never even heard of them!

 

Lol. They're punk pop based in Dallas but getting pretty national lately.