When my 2005 F-150 goes over 55-60 mph
it overheats . already replaced the
thermostat what could it be?
Could be the impeller on the water pump is eroded away, or a plugged radiator.
Did you ever use radiator stop leak? If yes then you have a serious issue of clogged cores. If no is the answer then you may have to flush out your radiator anyways. When higher speed occur the engine demands more coolamt to cool the engine. Also did you check timing? Sometimes misfire can overheat the engine aswell
Use the cock on the bottom of the radiator and drain out some coolant. If it is rusty brown maybe you can flush the radiator and system to clear up any clogs. Never use tap water when mixing antifreeze. Use only distilled water. Also check the thermostat for function. Remove the thermostat. Bring a pot of water to a boil and drop it in. It should open easily.
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