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A Hot Toyota

Q. Hello - I have a question about a 1983 Toyota Supra, 2.8L 6 cyl.: Overheats when traveling at high speed ... above 60 mph.. worse with A/C on. I live in South Fla. and this is a new problem since its gotten "hot" -- 80 deg and above. Mechanic believes it's the "fan clutch". Do you have any other suggestions??

Radiator/ thermostat/ radiator cap have been recently replaced Related or not, the car has had many A/C problems and the A/C, even when in top shape (even when the car was new), is not really cold. I have had this car since new.

Thanks.

A. A bad fan clutch is definitely a possibility. The fan clutch has a bi-metallic spring in the front face that expands and contracts to a change in temperature. The incoming air either heats or cools this element causing the cooling fan to either lock or unlock to the fan clutch. The principle behind this is at higher speeds the air coming in through the radiator is enough to cool the engine. If the incoming air is not enough to do the cooling job, then the fan will engage pulling in more air. This is done to help improve fuel economy because a fan without a clutch will use about 4 to 5 horsepower.

About the only way to test a fan clutch is to let the engine run with the hood closed and listen to it. When the engine starts to heat up their will be a distinct change of sound in the fan. I can't really describe the sound, but you will know it when you hear it. Turning the A/C on while it's idling will help insure that it will kick in if it's going to. Radiators are usually sealed around the mounting frame, and Toyota does do this. Make sure all the air guides and baffles are in place to be sure the incoming air is directed through, and not around, the radiator.

Some other possibilities are a loose fan belt, a weak water pump or partially clogged block water passages. The higher the milage on the car, the more distinct the possibility of either one being a problem.

Inside the water pump is an impeller that pushes the coolant through the engine. Over time that impeller will wear down until it can not push the coolant at the proper speed and volume to cool the engine. There are no external signs to look for, the only way to tell is to remove the pump and visually inspect the impeller. Of course if you are going to go through the effort to do that, it would be a good idea to just replace it, especially if it is the original water pump.

In a high milage car rust and sludge can build up inside the water passages in the engine block, partially or completely blocking some of them. Flushing the radiator will not clean out this sludge. You need to go to a shop that has the equipment to do a reverse power flush. What this will do is push high pressure cleaner through the block in the reverse direction of the water flow to push all the gunk out. I have seen some that were so clogged that I had to take the expansion plugs out and dig the gunk out with scrappers and whatever tools I could get into the passages.

The added strain of removing heat from the A/C system would only compound the problem and cause a drop in A/C performance. When the cooling system problem is fixed, the A/C performance will increase as well, althought I suspect a seperate problem with the A/C since it exisited before the overheating problem.

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Additional Information provided courtesy of AllDATA and Warranty Direct
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