Your 1983 Toyota supra keeps overheating?

Answer 1

There are a million reasons why a Toyota Supra (nice car!) or ANY car can keep overheating. Here are a few, from most likely to least likely (but still very possible).

1. The engine is low on coolant, or leaking coolant. Also, some cooling systems need to be refilled a certain way to eliminate air bubbles, which otherwise can prevent you from adding enough water. I've owned a Mazda, a VW and a BMW which all fooled me at one time or another with air bubbles in the cooling system.
2. The coolant is rusty or contaminated. Also, all engines should be cooled with a mixture of water and anti-freeze. Water alone is less efficient at transferring heat, and anti-freeze also contains additives that lubricate the water pump bearing and help prevent corrosion.
3. Coolant is not circulating properly through the engine. Possible reasons include old rubber water pipes that collapse when hot coolant is running through them (but seem OK otherwise), or excessive rust or scale in the engine's water passages. If the problem isn't too extreme, "flush and fill" kits from auto parts stores can help.
4. The thermostat is stuck closed, or partly closed, or the radiator cap is not holding sufficient pressure. Replacements are cheap. Do NOT buy a "cooler" thermostat hoping to solve the problem -- it probably won't. But if it does, an engine that continuously runs cooler than what it is designed for is likely to develop other problems, including oil sludge.
5. The radiator is partly restricted or plugged -- this is very likely if it's never been replaced on a 27-year-old car.
6. The cooling fan (if belt-driven) is not working properly. The bearings could be worn. The center thermostat on the fan hub, if equipped that way, may be worn out. The belt could be slipping. If the fan is electric, a temperature sensor or relay may not be working properly.
7. An auxiliary radiator fan is not turning on automatically when the a/c is turned on -- see previous item for possible causes.
8. There is some kind of physical blockage (leaves, sticks etc.) in front of the radiator, or airflow guides behind the radiator are damaged or missing. On some cars, if the plastic trim pieces under the engine are missing, cooling air will no longer be diverted properly toward the radiator.
9. The external oil cooler, if equipped, is clogged. Oil will still circulate, but it won't be cooled properly.
10. Driving conditions are too extreme. For many cars of the '80s and earlier (especially British cars), they simply weren't designed to cope with stop-and-go traffic and temperatures in the 90s.
11. The fuel system is running too lean, making the engine run too hot. (This is not a trivial problem -- excessive heat in the combustion chambers can quickly ruin an engine.) This can be caused by a defective oxygen sensor, although they are supposed to default to a "rich" fuel mixture (which burns cool) if something goes wrong with the system.
12. The car is carrying too much weight, or pulling a heavy trailer. (Hey, somebody installed a small trailer hitch on my 1990 Nissan 300ZX before I bought it -- I hope it was only for a bike rack.)

Probably 90 percent of cooling problems are related to answers 1-5, so start there.