I had to swap motors in my 1996 es300 (rod bearing), so I had my mechanic put in a good (?) junkyard motor that had 120,000 miles on it. It runs purrrrfect now sitting still. I idled it for two hours with no problem, but if I drive it down the road, it overheats. I am at a loss. Can anyone help me out? Thanks.

hate to say it but it may be a head issue.

could be head gasket or cracked head.but look in your radiator see if it's circulating if not could water pump....

Clogged radiator?

The car didn't overheat with the other engine, so I'm thinking it cant be the rediator. I guess that leaves the heads or the water pump. Since the cap isn't on top of the radiator, it's kinda hard to see how well the water is moving. I guess a compression test would eliminate (or point to) the heads, which should only leave water pump???

Welcome to the AF!

Could be your thermostat. If it won't open very far, it would produce the symptoms you describe.

the actual junkyard motor is probably the problem. drain the oil out and see if the oil looks a milky brown. that would tell you it is a head gasket problem.