[Razorback1980]

I would check for air in the system first. That could be one cause as Jon suggested. I don't think it's the thermostat as it wouldn't stay cool at all if it were stuck shut or partially shut. Check out the for sale site here, someone was selling a brand new aluminum one with a larger capacity. If they had been made for an automatic, I would have bought one. I don't agree with buying a used radiator...some things can be used but not all....you may end up with the same problem.