I have a 2003 f-150 fx4 4x4 with the 5.4 V8.

While driving on the highway at 60 mph the coolant temp shot all the way to the top and the coolant warning light came on along with the check engine light( code P1299). I pulled over and all the coolant was leaking out but I couldn’t see from where and the coolant reservoir was empty. I put a couple of gallons of water in and drove the 2 miles home. Once home I put in some coolant and ran the engine and found no leaking. Any ideas to what may have happened and where the leak may have been from? Code P1299 is for cylinder head over temperature protection active.

 

Any sign of leakage from the water pump weep hole? Check all of the hoses and clamps. Hopefully it's not a head gasket issue.

 

Putting (relatively) cold water in a hot engine can be as damaging -or worse- than the initial overheat. Be careful doing this. The other questions are, how hot and how long? Only time will tell if you have any engine damage. My primary suspects would be 1) failed thermostat. 2) a leak in the system.

 

Yeah I bet steam was rolling out of it if he put cold water in it

 

Weep hole looks dry. Once a get a day off I’ll be checking all the hoses and clamps

 

It sat for 30 minutes before I added water. The gauge was maxed out but no steam coming from the engine, just coolant from somewhere. I had the engine shut off within 1 minute of the temp maxing out.

 

If it had overheated, it wouldn't run (right) again without a rebuild. It didn't overheat - it went into FSC, as this caption explains:


(phone app link)

I've driven on the highway at normal speed for half an hour in FSC, and didn't hurt the engine. Mine was caused by a VERY slow leak in the heater core that I never saw because it never got wet enough to drip - just a vague smell and the slightest wisps of vapor on the w/s. When I saw the coolant light & watched the gauge shoot to H, I realized it was protecting itself, and just kept going to the next place that looked like I could get some water. I looped the heater core off, dumped in some water, and finished my trip. When I got home, I replaced the core & coolant, and drove the same engine for another ~10 years without any problems.