Toyota Repair: toyota rebuilt engine, toyota pickup, toyotas

Question
We are looking to put a new engine in an 89 toyota pickup.  The last engine that was put in the car kept overheating and the mechanic said that it was a faulty thermostat.  So, after replacing the thermostat 3 times, the "new" engine finally blew.  I've heard a rumor that putting in newer engines in older toyotas can cause problems, any input on the subject?

Answer
The problem was probably with the cooling system,not enough circulation will cause overheating, obviously the thermostat was not the problem so it may have been something else, what engine was put into the truck,normally installing a rebuilt or remanufactured engine does not cause problems unless there is another problem which causes failure of the new engine.Maybe some more clarification would help.