I have a 97 F-150 5.4l 4WD. I am having a problem while driving the temp gauge goes all the way hot and the dummy light comes on. The first couple of times this happened I pulled over to check for overheating and found nothing. Whenever the truck does this I can shut it off going down the road and restart it and it's fine for awhile. Sometimes the gauge will stay hot for a minute and then go back to normal. I have changed the thermostat to eliminate that. It has plenty of coolant and no apparent leaks. It doesn't matter if the gas tank is full or empty. It appears there is some type of pattern that it only happens while the A/C is on and usually cruising down the highway at a constant speed. Does this sound like a faulty temp sensor somewhere? Any ideas will be appreciated!

Hank

 

Run an OBDII scan and see if you have any stored codes for the CHT (Cylinder Head Temp) sensor.

Have you also gotten a CEL in conjunction with this symptom?

Steve

 

If you have access to a digital multimeter with temperature capabilities, I'd try to read what the actual temp is when you're getting these readings, other readers might have a better idea of where to put the probe, but I'd think if you taped/fastened it to the radiator tank, so it's snug up against it, or, perhaps better, put it in the coolant in the expansion bottle, at that temp there should be plenty of warm fluid in there....oh and make sure the probe's waterproof....

Are you certain your engine is NOT overheating? Is your thermostat in the upper hose (assuming they still have them) is opening and closing properly? One that sticks might cause behaviour like that...also, have you checked that your fan is running properly?

 

I have an 99 F150 with the 4.2 and was having overheating problems. Changed thermostat, cap and coolant with no success. Finally cleaned the outside of the radiator with degreaser and water. Basicallyu sprayed the the radiator externally with degreaser, let set and rinsed with garden hose. This helped. So far temperature is running at 215 F max compared to previos max. of ~ 238 F.