masonv512

Just bought this f150 and it ran fine for a while. except it was heating up just a little over normal. Now the engine intermittently overheats and boils over but the temp doesnt show in the red. Also when it is hot the heat blows cold... thought it was a clogged heater core and flushed it and the whole system. Minor improvement and then back to freezing cold in a day. Just replaced the thermostat as well. Also the lights dim when i use pwr windows or other accessories. Is this a ground issue possibly? Anyways to test this? Im getting a pressure tester to check the cooling system for leaks tomorrow. Any other simple ways to check other components of the system? Anyone have the same problem?

masonv512

Replaced water pump and some old looking hoses, replaced thermostat again because thought it may have been faulty but nope. Refilled and burped the system. Truck runs cool now but still don't have any heat. Both heater core hoses seemed cool compared to upper rad hose and still no heat in cab! Worked randomly for about 5 minutes then gone again!

Any help or ideas would be greatly appreciated. Thank you in advance

masonv512

Flushed the heater core again with CLR this time. Some junk came out. Refilled system Burped it. Then took it for a test run. Had heat while idling and driving normally. Then going up a big hill the heat suddenly went cold and the temp started to rise but did not over heat. Seriously What the hell is going on!?

Anyone please? Thanks in advance

Freudslipped

Are you losing fluid when this happens?

Did you replace the radiator cap?

When you preasure tested the system, did you pull the plugs?

I had something very similar years ago. It turned out to be a cracked head gasket.