I have an issue on my 83 trans am where the AC is running causing the car to want to over heat? When the AC is off, the engine runs at the same temp consistently and rarely see a temp change when it's at running temp. However, if i turn the AC on, the temp will climb to the point where it wants to overheat.

my thermostat keeps going bad and i have a mechanical fan the

the fan clutch works and the radiator is in top notch condition

 

I assume that your fan shroud is in good shape as well. I dont believe your 83 has an electric condensor fan. It would be in front of the condensor,radiator assembly. The most common causes of overheating during AC use are failure of the condensor fan(when so equipped), insufficient radiator function, failure of the fan clutch.

You say that your radiator is in great shape and that your fan clutch works. Have you performed a core temp test on the rad when this problem was occurring? You do this using an infared thermometer and looking for differences in temp between tubes. This test is to look for restricted tubes. Or have you replaced the radiator recently?

Also, regular thermostat failures? Do you mean that they fail after the engine has overheated several times due to the AC issue? Or is the engine overheating at other times and you replace the T-stat for this reason? Thermostats are simple devices. They dont fail that often unless theyre overheated. What shape is your coolant in? Have you flushed the system recently?

 

No i have not replaced the radiator and it is factroy, the factory waterpump was replaced in April, the coolant was flushed in 2009. the coolant is in great shape i replaced the thermostat for overheating and it was factory

now it only overheats when the ac is on

 

I do not have an infrared thermometer, but will a fluke temperture probe work?
this all starting happening recently and never happened before

 

Make sure your radiator and condensor are clean and check out the clutch fan again. I had one that seemed to work fine but the truck got really hot when the ac was on. Once I replaced it things went back to normal.

 

If you can access all tubes on the radiator while at temp, the probe might work. Again, the purpose is to compare tempuratures between tubes. What I have found several times has been the lower portion of the radiator restricted. Its like having half a radiator. It still functions and cools to the motor until there is any real stress on it. Such as when the AC is running.

This type of failure can even lead to misdiagnosis of the fan clutch. The fan wont seem to function properly. This due the fact that the restricted radiator does not release sufficient heat to bring the thermostatic clutch up to temp. Basically, if the fan feels stiff to turn with engine off and the bearing is good, its probably fine. Your type of symptom is most always a restricted radiator.

 

P.S. when checking the fan clutch, be sure to look for oil leakage from the clutch either at the shaft seal at the rear of the clutch or at the sensor "pin" at the front of the clutch. The clutch is hydrostatic and filled with viscuous fluid. If the fluid leaks out, it will malfunction.

 

well when i turn the ac on my mechanical fan actually slows down a bit and then speeds up when i turn it off

 

Are you sure its not just the compressor pulling down idle speed?

 

yes but Is that normal with these cars?

 

as whats is happening to 91notch: I have to turn the AC off and turn the heat on to pull the heat out of the engine until it goes back to normal running temp and stays there.

the fan is working as it should but i found out it does not have a clutch and runs all the time

 

bump

 

I appologize Kitt, I just cleared my thread list of about 100 threads that Im not following anymore. I was getting lost and forgetting people.

Some drop in rpm is normal but should only be momentary as the ECM takes a moment to correct idle by openning up the IAC. I would suggest an IAC check. Unplug it while the engine is idling and the rpm should increase. If not it may be bad. You can check it with an ohmmeter.

So, no fan clutch. Have you checked your radiator any further? Im quite certain thats where your problem lies. In fact, I am the guy who always says to test before you replace. But in your case, I feel quite confident in saying, replace the radiator.

 

Btw Kitt, Be sure to replace your t-stat and flush coolant when you replace the rad. New rad cap as well.

 

thanks for helping me out

 

what is your opinion on thermostats? Is acdelco or motorad fail safe better? 180 degree or 195 degrees (stock)?

 

does it over heat on the highway or around town? My first thought is that you need an air dam

 

it overheats both on the highway and city, usually 10-20 or 20-30 minutes in traffic. if i dont use the a/c it never over heats

i will have to check if it fell off, in boston there alots of pot holes

what does the air dam look like? i have heard there are different styles

 

when the temp gauge is showing hot,is there any
boiling,hot odor,or other evidence of actual overheating?
-certain electrical problems,including a bad engine
ground can produce a false gauge reading-the A/C
blower pulls a fair amount of current while running at
high speed which can affect a bad ground or other
electrical problem while the A/C is in use causing a
false reading(try the blower on high with the A/C
inactive to see if the gauge reading changes)
If the flex fan is a street type and not a "drag race"type,
you can pretty much rule out any airflow problems
even if the airdam is missing(airdam is important with
electric or clutch fans though)
Does kinda sound like an internally dirty radiator if
actual overheating is occuring-the aluminum core ones
in particular seem to oxidize internally and become
ineffective sometimes

 

There are several different schools of thought on this. I believe that on a stock motor, we shouldnt go below 180. 195, even with lower fan temps wont lower your operating temp much. Ive always felt that 195 is too hot for a performance engine. Stant "Gold" is a good brand.

 

yes there is burning odor

 

the air dam is a large piece of plastic that sticks down like a wall from the radiator. it's about 3 feet by 8 inches

 

The air dam simply helps reduce the need for the cooling fan at higher speeds by diverting air through the radiator. Its of some value to you, but your non thermostatic, mechanical fan runs with engine speed, which means it runs all the time anyway. The air dam is of greater value on cars with electric cooling fans, where it saves fuel and power by reducing the fan(s) on time. The air dam has no affect whatsoever in stop and go traffic on any car.

Your initial problem is most certainly a restricted radiator core, as I and others have already told you. A thermal test of the radiator core would prove this. Since you are unable to perform this test, and your radiator is original, I feel quite confident in recommending you replace your radiator.

The radiator will fix your problem. The air dam is something you can look at as an upgrade.

 

thanks for the help guys i am more used to working on newer cars but it is nice to work on older cars.

 

I am going to need a new radiator, I found some cracks in my radiator and the GM part numbers.

 

If you dont mind spending just a little more for a much better product, There are a few different all aluminum radiators on the market today. Thats going to be the next upgrade I make. Check out Summit Racing for some options.

 

What radiators do you recommend?

http://www.summitracing.com/parts/SUM-380455/
http://www.summitracing.com/parts/PLI-433918/

 

I'm using the Summit 380455 radiator. Summit calls it a direct fit but it is not. In my car it took a little work to fit it in. In hot weather with the A/C on it would slowly heat up in stop an go traffic. Otherwise it was just fine.

I ran across an article on fan placement in relation to the radiator and they had the best results with the blades being 1"-1.125" from the radiator. Mine were around 1/2". So yesterday I spaced the fans out closer to one inch. Driving home this afternoon coming down the freeway with the A/C on the car was running as cool as it ever has and that includes no A/C. I found that interesting. I will have to wait for some real hot weather and see what happens then.

Edit: If you are running a single fan you might want to consider the Ford Taurus fan from the early to mid 90's. They are cheap to buy and are one of the most powerfull fans you can buy. Some on this forum have gone that route with great success. I have seen good results with the Taurus fan on other forums as well.

 

Fan spacing is a very important point. Its interesting to note that the fan being too close the the rad actually reduces efficiency. This has to do with the fans vortex effect and the need for adequate clearance for this to take place. With the use of a proper shroud, it is best to leave 1.5 to 2 inches between fan and rad.

Another major point is fan design. The taurus fan is unfortunately an electric type. Kitt"s 83 uses a mechanical fan. I dont think that switching to an electric will improve his cooling. A good six blade fan, whether its a flex or clutch type should work well.

 

the radiator has been replaced and it stopped overheating with the a/c on.

but since my thermostat housing cracked about 3 weeks ago. it started to overheating with a/c on again.

I also cannot find a crossfire injection water outlet/thermostat housing. Every one I found does not fit and the hose neck angle is way off.(napa, oehq, rock auto, and etc) it keeps hitting the a/c compressor. Does anyone have a CFI theromostat housing or know a suitable replacement?