Why does my 1988 Toyota keep overheating?

"sometimes thermostats are f'd up from factory . you can check it by taking it out and putting it in a pot of hot water on the stove. if it opens then its probably good.

also you have to make sure that it is going in the right direction with the spring side facing into the block.

also flushing out the radiator is good but did you check if you were getting flow through to begin with?

also a lower temp thermostat will do the trick sometimes, as it will open sooner and let the coolant through- thus keeping it cooler. however, if you live in a cold climate you would have to change out the 'stat seasonally."

Are we sure it's overheating? You could possibly have a bad temperature sending unit. use an ohm meter, the sending unit should read from 0-5 volts, 0 at cold, 5v is overheat. so if that motor is barely warm but it's showing 5 volts the sensors bad. If it's actually running like it's overheating, and your sure it is, try retarding the timing if it seems like it's worse, then advance the timing. Easy to do, losen the holddown clamp on the distributor, enough so you can turn the distributor counter clockwise and clockwise while it's running. if the timing is too advanced it causes a lean condition, which will overheat it. as you turn the distributor back and forth, one way will cause engine speed to increase, the other will slow it down. Find a spot where the idle is reasonable around 5-700rpm tight the distributor and try it. I would say use a timing light, but since I also experienced this problem on mine, when it was timed according to spec it would run hardly, probably because the distributor was a tooth off, the points were bad, or the timing belt jumped a notch. hope this helps