Original owner of a 2005 Excursion 6.8l v10, 155k miles.
About a month ago 10-15 minutes or so into my ride to work on a 50-60 degree morning the check gauges light comes on, noticed the temp gauge pegged to H followed by the check engine light, then limp mode. Turned on front & rear heaters and cold air was blowing. Pulled over, checked under the hood, coolant wasn't boiling, tank was 1/2 full and cold air was blowing thru radiator. 1st thought was T'Stat. So I removed T'Stat added some antifreeze & continued to work w/o a t'stat. Then had heat thru radiator & heat in front & rear heaters. Engine ran cool with no overheat issue. Bought aftermarker T'Stat (slant) put that in and everything back to normal. About a month later same problem happens at about the same point in my trip to work, temp pegs, no heat from heater and goes into limp mode. Shut the truck off release pressure from radiator and coolant level goes down, seems to feed back into engine. Start the truck up temp goes back to normal and everything is fine for the rest of the day with several starts/stops. Bought FORD OEM T'Stat & replaced. Next morning same problem. So i think maybe there's an air pocket somewhere, add more coolant & fill to proper level when cold. next morning from cold start same problem. Coolant is clean, just changed oil and no coolant in oil. Problem only happens from a cold startup in the morning.
I'm at a loss.
I'm thinking of drilling a small bypass hole in the T'Stat.
Can anyone suggest a possible cause?

 

The Motorcraft stat has that hole in it. You can burp it by removing the hose on the pipe at the right front of the intake .......I did a write up on it a while back. Is that a Mtrcrft stat in there? They will limp with no signs of overheating and can be a mystery. Some claim it is the sender under the intake.....there are more posts on that, do a search. It could be a marathon problem so replace the plastic heater bypass valve and the rad cap before proceeding.

 

Did it suddenly jump up to Hot, or did it do so gradually?

 

They always jump if past the middle. The oil light should come on too.

 

I've been trying to chase this one down myself. Mine did the exact same thing this past weekend. 2nd time it's happened. The first one, I replaced the t stat and was good for over a year. Did that this weekend on the way home and ran in limp mode for the remaining hour and a half of my trip. I'm at a loss and need help. My web searches have turned up the same issue over and over with no solution. If I find anything, I'll share. Good luck.

 

Dealt with this myself last year. Oil light came on, few seconds later temp gauge pegs to hot, then limp mode. Shut truck off and restart - all normal again. Second time I was stuck somewhere I couldn't stop and shut truck off and I spewed antifreeze out like a geyser.

Replaced what I found to be a non OEM stat that was in the truck when I got it and did a full flush on the system. Took several days of "burping" before it was right but after that I haven't had an issue since.

I'm leaning toward you have air in your system and would recommend you do a flush and then burp the air daily for a few days following the flush.

 

Somehow, it does not seem foreign to my brain to associate Christina with burping.

 

Here;
https://www.ford-trucks.com/forums/1...l#post14031875

 

Ummmm {BELCH}

 

Must be your first burp ever.