Asked by Apr 15, 2012 at 12:05 PM about the 1969 Pontiac Firebird

Question type: Maintenance & Repair

My 1964, 389 pontiac motor thats been bored out to a 410 has a very bad overheating problem.  All the obvious has been replaced; including the water-pump, thermostat, radiator and the hoses.  It appears to be building up pressure in the block, behind the thermostat.  Temperature reaches over 250 within a half hour afte startup.  WTF is wrong?

10 Answers


Did you replace your Radiator Cap when you installed the new Radiator? How's your timing?

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how is the vaccuum advance? my former 70 Le Sabre would overheat like that and the buyer just replaced it to restore the engine.

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was the spacer behind the water pump reinstalled, very important to get coolant flowing correctly

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bbuilding preesure behind the thermostat, easy mistake is thermostat put in backwards

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two bolts easy check

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is there a shroud with the radiator? sometimes that is needed to get the air going thru radiator to help it cool

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did u put the thermostat in assbackwards?? i know its a simple task but that can cause it to overheat


last but not least i have had great luck with aluminum radiators, and some friends use electric fans

did it over heat before you had the work done ? are you using a 4 core radiator? you might need a high flow water pump . a shrowd is also a big help. in fact i need one for my car .

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could be an air pocket ,let warm up with the cap off ,when the thermostat opens it will either start flowing or in will drop down real fast. if it does ,that was the air pocket filling up. just add more anti freeze and put the cap on .

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