Overheating 1973 455 Buick Regal

[buick1]

My dad purchased a 1973 Buick Regal last year. He put a 455 big block into it. Everything was fine until he took it to the drag strip and blew it up. Since then he has had the motor rebuilt and rebored to a 462. He put the rebuilt motor back in the car and it was running fine until a few weeks ago it starting overheating and he can't seem to figure out why. He is supposed to race in a few days but the car keeps overheating and he isn't sure what all might be causing the problem. He has put alot of money and time into this car and he really wants to race it. It is very frustrating for him not to know what the problem is. He has tried different methods of fixing it but so far no such luck. He works alot and doesn't have much time to work on it or diagnose the problem. So that is why I am on here asking for some smart guys help. I'm sorry if my car lingo isn't as good as yours but I am only 16 and have no idea about cars or what even makes them start other than the keys of course. So I would really appreciate someones help to make my father happy.

 

[rcull]

Was a big enough rad put in when the conversion took place, was it a new one or at least one know to be clean? Is the clutch fan working properly, if it has one?

What are the conditions it heats up under. When it starts up, does it just warm up and go straight on up to hot like the thermostat is stuck or air locked (drill a 1/16th inch hole in the thermostat)?

When the engine was rebuilt, was the block hot tanked?