I have an '85 F150 with a straight 6 300 engine in it. It sat in my brother-in-laws driveway for 3 years, never being started. I put a new battery in it, changed fuel filter, changed oil, oil filter, air filter, and drained and flushed radiator and replaced thermostat. After idling 20 minutes, it will overheat. AFter turning engine off, air will bubble back into reservoir. However, it is not losing water, and there is no oil in water, and no water in oil, so I do not think head gasket is blown. What else could be causing it to overheat?

I have an '85 F150 with a straight 6 300 engine in it. It sat in my brother-in-laws driveway for 3 years, never being started. I put a new battery in it, changed fuel filter, changed oil, oil filter, air filter, and drained and flushed radiator and replaced thermostat. After idling 20 minutes, it will overheat. AFter turning engine off, air will bubble back into reservoir. However, it is not losing water, and there is no oil in water, and no water in oil, so i do not think head gasket is blown. What else could be causing it to overheat?
I think if bubbling into resivor, probably going to be headgasket , its probably just weak now but will show more signs as time passes, have a compression check done.

Hi
More often than not your radiator is shot and no amount of flushing it will solve the problem other than a new one! Hope this helps!:D

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