My 62 ranchero straight six has has overheating problems since buying it a few weeks ago. The radiator was flushed and overflow added. What happens is when it's driven for over 30 minutes the radiator backs up into the overflow, and it has come to the point where the overflow is overflowing. Does the 62 have an thermostat that I can remove if it's sticking? Otherwise what's happening here? Thanks all.