I Have a 78 F150 with a 351M. For the past week or so my truck has started to get really hot when idiling and even when driving down the road. I figured my thermostat was stuck closed so I put a new one in and it still overheats sitting at idle. Could this be a different problem than the thermostat? I dunno but its makin me mad lol. If anyone could give me some quick help I would really appreciate it. I have checked the coolant, its fine and full. I just dont know. Anyone?

 

If you have a clutch drive fan, check the clutch.

 

Is this the stock temperature gauge telling you, or an aftermarket mechanical gauge with actual numbers?

 

Might want to try a new radiator cap too.

 

Pull the radiator cap and let get warm. Look in top of radiator and see if the water is flowing. The fan clutch being bad will make it overheat at idle but going over 20 mph the fan clutch is not supposed to be a factor. Air flow across radiator at road speed is supposed to cool it enough. I have seen the fins on the water pump completly rusted off and just a flat plate was left to move the water. Check the flow and then check to make sure one of your hoses is not colapsed. The spring inside the hose is supposed to prevent this. The spring could be rotted away.

 

This is why I suggested the fan clutch