2003 F250 5.4V8 false overheat problem(I know...you've heard this one before). I've read a lot of posts that hit on this topic, but I haven't been able to solve it. Ford dealer can't figure it out either, they just want to sell me a new engine. Any help would be appreciated.

After a cold start, the truck warms up properly and warm air starts to blow from the heater. Then the air starts to cool and the temp gauge starts to rise. Soon afterwards, coolant is forced out through the reservoir cap, then it goes into the 4 cylinder protection mode, check gauge warning, check engine light comes on, code P1299.

Then I turn the truck off, sit a few seconds, turn it back on and all’s fine. Temp gauge is right where it should be, no more leaking fluid. I can drive all around town and don't have a problem until I let it cool down for several hours. I measured the cylinder head temperature (CHT) sensor resistance during both normal and failure conditions and it reads the same. Checked the cylinder head temp with an IR thermometer and it reads normal all the time, not really overheating.

Several posts suggest a blown head gasket, but if that were the case, why does the problem go away after I turn it off and back on? I think the temp gauge is controlled by the PCM rather than actually reading the sensor (is this true?). If the PCM is getting a good reading from the CHT sensor, what other input could it be getting that would cause the temp gauge to rise? Thermostat has been changed twice.

 

You need to replace your thermostat and not with a parts house one it needs to be a motorcraft one...

 

And its not a false overheat, If coolant is coming out of the degas bottle the motor is overheated!!! Read this link he was having the exact same problems as up,,,,,Update; Radiator spewing and limp mode fixed, with pictures

 

The ford dealer replaced the thermostat, I assume they used motorcraft, same problem. I stated it was a false indication for two reasons 1) i read the external temp with a ir thermometer in several locations and theres no difference between problem and no problem, 2) when I turn the engine off and back on, the temp is normal. How can that much mass cool down that quick?

 

Usually what happens in this situation is that when you turn the truck off for that short time it gives the thermostat a chance to sit in the hot water and finally open. Once open you wont have a problem with it untill it cools down enough to close the stat and then the whole process repeats itself. I guess I would make sure number one that they are really changing the stat when they tell you they are and number two that they are using a motorcraft stat. Its not that tough of a job and if it were me I would be changing it myself so I know its done right...

 

I just pulled the stat and it's a motrocraft rt-1196. I think it's supposed to open at 190-192°. I'm with you on doing it myself, but I don't have enough info on how the cooling system works on this truck to figure it out.

 

You just pulled the stat out of the truck or is that what the repair invoice indicates they put in?? Replacement is pretty straight forward its right on top of the engine. I am sure you could IM EXV10 and he could walk you right through it..

 

No, no, no..I pulled it out an looked at it. I'm a motorhead, I tear cars/trucks apart and restore them and put them back together again. I fix everything myself....usually. That's why I say if I can figure out how this system functions, I'll be able to find the problem and fix it. I'm thinking if the PCM drives the gauge, and the CHT sensor is not the problem, then what other inputs to the PCM could cause this? Maybe that'll point me in the right direction.

 

There is nothing in the PCM that can cause the coolant bottle to blow out coolant. Only two things can cause the issue you are having either the stat is sticking or the headgasket is pressurizing the system. If you were just dealing with a gauge/ limp mode issue then you can suspect sensor /PCM issue but the degas bottle is telling you a whole nother thing...

 

OK, I guess I'll be looking at pulling the heads. Crap! I'll let ya know the outcome. Thanks for your help.

 

Good luck and keep us posted..

 

I guess before I went through all the work of pulling the heads I would remove the stat completely and see if the problem still exists, If it does then you know its probably a head gasket.

 

Wait. You are definitely not troubleshooting the heads or gaskets first!! That's a huge project to go after w/o more evidence!!

How long after you start the truck does fluid blow out the degas bottle? The reason some have suggested the head is a leaky head gasket will introduce a LOT of pressure into the coolant system. The engine need not be warmed-up, either. I looked at a car for my daughter and the pressure was at like 18-20 psi within a minute of start-up. I was 100% sure it was a bad head gasket and passed on the car.

I was one of those who had a lot of posts about the "false" overheat. You may be dealing with more than one issue here. My truck NEVER lost fluid. It would go into "limp" mode at the WORST times, too; hauling my trailer up a long hill in W. Va. and the truck would BARELY be able to get to the side of the road.

I will tell you I got tired of trying to chase down the issue. I went all-out. Even if you do everything I am about to mention, it will still be less time and money then messing with the heads!!

If this works it should cure any "false" overheat issue or even real issue. But, if there is a problem with the heads or gaskets, it won't fix that so proceed with that knowledge.

I replaced upper/lower and oil-cooler hoses. I replaced waterpump and fan clutch and thermostat (kept old one b/c I felt it was still working and threw in toolbox). I also replaced the aging radiator with a new DUAL-core radiator!! It has twice the volume of the original. One of my best investments!

The truck ran "cooler" but I still have the "false" overheat. SIGH

I replaced the CHT sensor. Do NOT follow the book and remove the entire intake!! Remove the alternator and the CHT sensor is right there on the left head (as seated in the driver's seat which is how all left/right nomenclature is oriented). Ok, the driver's side head!!

I had to bend a wrench to fit in there - just heated it up and smashed it with the hammer a few times. A socket won't work there is not enough room above the sensor.

At first this didn't seem to work either. After 3-4 days of driving - I haven't seen that issue appear again!! This is hauling a 24' box trailer in W. Va. mountain on 90+ degree days with the windows closed and the A/C on full and NO issues!!

 

He is blowing coolant out of the degas bottle within a minute or two of a cold start. It is not a sensor or the fan clutch , after he shuts it off and restarts the condition goes away until the next cold start. That would lead me to believe the radiator and hoses are fine as well. EXV10 had the identical issue as the OP and it was the thermostat.

 

If it happens 1-2 minutes after a cold start the t-stat shouldn't be opening anyway. I see now he said "properly warms up". I stuck t-stat will cause what you are seeing, OP.

However, when is your truck going into limp mode? Once you shut-down and restart does this problem ever happen? Have you stressed the truck to find out; towing, driving mountain roads, etc.? Hook up a trailer and find some hills. See if that gauge climbs up quick!! My truck would run at normal temp during day-to-day driving. The problem would arise when the motor was being stressed.

About 85-90 on the freeway would see the gauge rise way up there but not quite cause it to reach limp-mode, but it ran MUCH hotter than it should have been. As you said, even if the engine returns to "normal" operating temperature the gauge will NOT reflect that until you turn off the motor and restart.

I also installed an Autometer water temp gauge and will not trust the factory gauge again.

After the work, I noticed a DRAMATIC difference in the temps of the motor. Even with it being stressed with a load, hills, etc, etc. I never see the north side of 195.

This wouldn't explain the "limp mode" but a bad cap could explain the coolant puking out!! Of all the times mine did "overheat" I never lost fluid which is how I realized the truck wasn't overheating.