I figured out that my car only runs hot (230*-240*) w/ the A/C on, and at high speeds. With the A/C off, it runs like it should(around 200*). What's goin on?

 

Any help here?

 

The overheat may only occur when the A/C is on, but it isn't the A/C's fault. The cooling system doesn't have the 'cooling capacity' to keep the engine cool and run the A/C. The problem could be any part of the cooling system. You might start by flushing the system and filling it up with new coolant. Then clean the radiator fins.

 

The rad. is only 1 year old. I took it out and had it cleaned not too long ago(2 months). Does the A/C really make it run that much hotter? What temps does everyone else see?

Edit: 500 posts.

 

in 95* weather, mine runs 180* with or without the a/c on the freeway going 70. does your's have the air deflector?

 

It doesn't have to run much hotter with the A/C if the radiator is just keeping up without the A/C on. Once the cooling system can't keep up, the temp will climb and climb. I run around 190 all summer long with or without the A/C on. As far as cleaning, I was talking about the outside of the rediator. Look up under the nose and see how much stuff is stuck in it. Absolutely need the air dam.

 

Yes airdam
Yes rad. clean in and out
aprox. 35/65 mix (more water)

I'm totally stumped. What temps does the A/C evaperator see? Could it be a vac. leak somewhere in the A/C that causes it to run lean and heat up? Are any of these possibilities? Help!!!

 

you still using the stock single core plastic/aluminum radiator?

If so, buy a new 3 core...either aluminum or copper/brass....you probably have a lot of corrosion and junk built up in the radiator and can't see it. my '88 would start to build heat until it would start to boil over. replaced the radiator and now it barely hits the 220 mark on the gauge. I am in Texas and we do get just a little hot here from time to time and naturally i run AC ALL THE TIME.....

 

92,

can you post some more maintenace history on the cooling system. ex what and if the radiator cap has been replaced, waterpump replaced, hoses replaced/inspected, and has the thermostat been replaced. you metioned some key points already so i won't go over those. another thing that it could be that the gauge/sending unit is incorrect which happens all too often. so dont rule that out. when refilling the cooling system did you bleed it? i'm sure there are more but these are just a few to help you diagnose the problem

these details may help us help you diagnose your problem without covering bases that have already been covered. well get to us with a report.

 

my car with a/c off runs 220, and that normal temp
my car with a/c on runs about the same because both fans are on.

 

It is a 3-core copper/brass rad. The rad. cap was replaced 2 months ago w/ a 331 16 lb. "lev-r-vent" Stant. The hoses were new when the engine was rebuilt in February. They're gate's hoses. The water pump was replaced in Feb. too b/c the old one started to leak. I forget what brand it is. There is no t-stat in there, for now. I'll put it back in when I figure out this problem. Also, the guy that owned the car before me gave me his receipts and they show it was overheating, so theyreplaced the sensor and gauge cluster 7/3/00. They charged him $500.

 

Try running it with a stat in. Use a 180º with 2 1/8" holes drilled in it. You can actually hotter without the stat because the fluid flows too quickly for proper heat transfer. IE the coolant doesn't stay in the rad long enough to cool down before moving back into the block. This could really be noticeable with a new water pump with perfect fins and an absolutely clean and free flowing cooling system. The coolant moves around so quickly it doesn't have time for optimal heat transfer. At high speeds it would be even worse due to increased rpms driving the pump.

 

It makes sense. I'll try it and see if it helps. Thanx.

 

92,
in my own experince, not to say that everyone has the same experince, my 3 row in my 86' ran 15* hotter than the 1 row aluminum oem radiator(same external conditons/tempertures). i assume the condensor is a-ok right(clean as a whistle no bent fins?) i assume that u have dual fans correct? if you do make sure that both are fully functional and the relays are ok. a failing relay can cause the a coolling fan to come on and off intermittently. last but not least... i would recommend a mechanical temp gauge to installed only temporarily to verify that the temperture is actually what is. even a new gauge/sending unit can be incorrrect as my friends 86' T/A proved. so don't rule that out quite just yet. or you can hook up a scan tool to check the coolant temp sensor reading and compare the reading to the temp guage. also if you have access to a scan tool check and see if your running lean under any driving condtions.

 

I'm going to have to say it's the thermostat. If you're running the stock chip, go pick up a 195 degree thermo. If you're modded, get the 160 or 180. You never told me at the show you had no thermo. I had a thermo get stuck open and it caused my car to overheat.