I have a 1997 Ply Neon. The head gasket failed and destroyed the engine (at 99,000), which I replaced with another. It now has a low mileage (unknown #) rebuilt engine and the radiator was replaced with a new one as well. I have had it 2 weeks and I am on my 3rd New radiator and I think it has failed as well. The engine seems to run very well and the heat guage operates at normal level. The problem is these radiators fail when I go to work ( I ride 65 mph for about 10-12 minutes twice a day). At the end of the runs in the morning, when it's about to fail, I see a puff of steam and when I check under the hood I see coolant on surfaces. The radiators seem to last from 2 days to a week. My mechanic thinks it's a bad run on the radiator manufacturers part, but, now I am wondering if there could be another cause?
It is possible for new parts to be defective, you could have the mechanic flush the system to see if there is any obstructions in the hoses, but you say the temp guage reads normal. There could also have been a bad temp sending unit in the used engine you put in and the engine is running hot