Hey this is my first post so a little paitence will be neccessary, and thanks in advance!
i have 1997 f150,2wdr,ext cab,4.6engine, lariat..150000mies
Normal driving, temp gauge all at once pegs to maximum temp, oil light comes on, check engine light on, fail-safe cooling comes on. I can put in neutral and switch off then restart , while rolling and all goes back to normal. sometimes it takes a few times to do this and then its good for the rest of the day. Engine is not hot at all. this is my work truck and when others have had it in the shop over the last 6 months, replace water pump, radiator, therostat, uper rad. hose and i think its all for nothing.
Any help would be great...thanks again....Doc

 

I wonder if there is an air bubble in the cooling system that tricks the temp sensor when it gets around it.

 

will simply burbing the system mend that?

 

My 05 5.4 with 90,000 was starting to show a similar symptom. It would not peg the gauges it would just go into failsafe. I would usually be able to clear by just turning engine off then restarting. But of late it started taking longer to clear, the last episode was when I was in the desert camping. I had to disconnect battery and let it sit overnite before it would clear, drove straight to the dealer, of course they could not duplicate and since I had disconnected the battery no codes. GOOD LUCK!

 

No, it reads actual head temp, not coolant. Sounds like you may have a bad temp sensor.

 

As LxMan1 said, sounds like the temp sensor. Actual temps don't change that rapidly.