HEYSEEOH

Hey, had a slight problem this morning. 2011 F150 6.2L motor. just over 100,000 miles on it, no modifications other than a cold air intake. No repairs or anything in the last few months aside from a few oil changes and a set of new tires.

Drove around for about 15 minutes and the temp gauge spiked and the warning told me the engine was overheating. I reacted by switching it to heat and cranking up the fan. Took a few seconds to park it in a safe place to figure out what was going on. Before I even tried to park it, literally within a few seconds the temperature started dropping rapidly and returned to normal at about the same time I put the truck in park. Opened the hood to assess what's going on. Coolant in the reservoir, radiator cap is cold to the touch but the radiator fan is in high gear. Turned off the truck and released the pressure in the radiator by turning the cap just a bit, which didn't take any longer than normal. No fountain of coolant or anything. Came to the conclusion that the truck wasn't actually overheating, just had a false reading on the temp gauge that caused a chain reaction of the temp gauge pegging, notification on the dash, and the radiator fan going at a higher setting than usual. Jumped back in it, temperature was normal and remained that way with no problems for the rest of the drive, approximately 20 mins. The only thing prior that I can think of that may be related is a slight bubbling of coolant on start up occasionally that goes away as soon as I start driving.

So to recap for the tl;dr:

• 15 mins into a drive the temp gauge pegged.
• Turned on the heat full blast, returned to normal temperature within a few seconds.
• Truck on, radiator cap cool to the touch, coolant in overflow reservoir, radiator fan on ludicrous speed almost plaid.
• Truck off, no bubbling, normal radiator pressure, no fountain of coolant with cap off within 2 or 3 minutes of shutting the truck off.
• Turned truck back on within 5 minutes and back on my way with normal temperature and operation for the remainder of the drive, approx. 20 mins of mostly back road driving, ~30-50 MPH.
• Other possibly related symptoms: bubbling upon starting the truck cold once in a while which goes away as soon as I start driving.

Where's a good place to start and test? My initial thought is that the temperature sensor is starting to go bad. Anyone know what the resistance is supposed to be across the terminals if I put an ohmmeter on it?

rrp0968

Sticking thermostat?

HEYSEEOH

Could be, that was another thought. Thermostat could be sticking shut causing the coolant that is in the motor to overheat. I was planning on replacing that tomorrow, or perhaps this evening. Do I need to use any kind of gasket sealer around the O-ring for the thermostat housing or is the O-ring sufficient?

rrp0968

I would use the o-ring only.