I know this is an old thread, but I just bought my 2005 4.6L F150 with 162,000 miles on it. I'm getting the overheating-but-not-really issue that this thread is all about.

I'm confident that it's not really overheating, because I can turn the engine off, wait 30 seconds and start it again, and everything is fine on the gauge cluster. Once in a while I get the P1299 code, and it goes into limp mode.

Here's what has me stumped. I can run the truck, AC blasting, 80 miles an hour all the way to work (about 25 miles) in the mornings, and the problem never shows itself. I can run the truck under 50 MPH and never have the problem. But, in the afternoons on my way home from work, with the AC on or off, within 5 miles it starts this overheating/check gauges nonsense. With the AC off, it takes longer to show up, but it will show up.

I'm really leaning toward an electrical problem, but I was hoping someone could shine some light on the problem for me and maybe point me in the right direction before I start throwing parts at it.

Thanks for all the help!

 

I had the same problem on a 5.4L I checked the wires going to the cylinder head temperature sensor and one wire was broke.. Replaced the wire and truck has ran great ever since..

 

My 2000 F150 5.4L stalled out about a month ago. Service engine light came on. It gave a p1285 and p1299 code. I reset it and it was working fine until the other day when it stalled 5 times in 2 days, temp gauge never moved always showed normal. Sometimes it started right back up others it let me sit for 10 min. Before it started. But this time when it happens no check engine light and no code readings are available. Also the mileage indicator goes out then comes back on after driving a few minutes. Thanks for any help.

 

I own a 2003 Ford E-150. I recently had a repair shop install a new intake manifold gasket. The shop also installed a new thermostat and performed a coolant flush. The next day while on a trip out of town the temp gauge spiked from normal to hot within a few seconds and the oil light came on. I pulled off the road and turned the engine off and waited 5 minutes and restarted the engine. The oil light was off and the temp gauge went back to normal. I never saw this happen before so I drove back to the repair shop to find out what the problem was. The repair shop said that it might be an air pocket in the coolant system. The next day I noticed that the coolant system was low in the de-gas bottle so I assumed that the air pocket had displaced some of the coolant. I filled the de-gas bottle to the coolant level line. A couple of weeks later I was headed out of town and again the temp gauge spiked, the oil light came on, and check engine light came on. I took the van back to the shop and they said the CHT sensor was bad so they replaced it. I also replaced the ECT sensor (an easy fix). A few days later the same thing happened again. except now the the engine went into limp mode. I turned the engine off and let it set for 5 minutes and then restarted and everything was normal, except the service engine soon light was still on. My OBD II tester indicated a 1299 code which is the CHT sensor detecting an overheating engine. I cleared the code and after letting the engine cool overnight I noticed that the coolant level in the de-gas bottle was below the fill line. This indicated another air pocket had entered the de-gas bottle and was most likely the cause of the false overheating. I recently drove the vehicle 200 miles and had no problems. There was also another occasion where the temp gauge spiked and I slowed down to 40 mph. After driving for a couple of minutes, the temp gauge suddenly returned to normal. Based on my observations and research, i decided that the cause of the problem was most likely air in the coolant system. The coolant mixture is a 50/50 mix of coolant and water and has a boiling point of around 223 deg. F. However, an air pocket could be 50 degrees hotter. The air pocket is essentially saturated steam under about 15 pounds of pressure. Steam tables show that saturated steam is at about 260 deg F at 15 psi. When that pocket of saturated steam passes near the CHT or ECT sensor it may cause the temp gauge to spike. I believe that the hot steam pocket may have fried the old original CHT sensor. These sensors are made of plastic metal, and thin wires. I guess I should have made the shop drain and refill the coolant system since they admitted that there could be an air pocket in the coolant.
If this problem occurs again i will update this reply.