I have a 2008 F350 6.4L diesel all factory setup with 390,000km. This truck has worked like a charm for years and still does most times. When I am hauling moderate to heavy loads the temp gauge will red line and the truck goes into limp mode. I immediately pull over and let the truck idle. In 3-4 minutes I am back to normal temperature. I shut the truck off and start it up to reset it and it will work fine for 10km or 100km. there seems to be no rhyme or reason. If the temp gauge red lines and I immediately pull over, pop the hood and open the rad overflow reservoir, there is absolutely no pressure build up. In the cases where I have shut the truck off it becomes very hard to start. It will roll over for minutes at a time before it starts. Normally even on a cold start you just touch the key and it fires up. I have already changed both thermostats and both temperature sensors. When hauling I always put it in tow/haul. There are no other codes coming up other then the overheat but I am convinced that it is not actually overheating. I am leaning towards a new computer but am looking for advice on other options first. Thanks

 

In that model year the #3 exhaust temp sensor will send excessive heat signals to the computer. As the sensors failed, they were replaced with a newer and different part number.

 

Change out your radiator cap pronto. The originals failed and will do exactly the symptoms your dealing with. If you want to isolate the problem for self assurance, have the old cap pressure tested to 16 psi, if it fails, there is your 14 dollar fix.

Fritz is spot on with the #3 egt probe as well.

Have you updated your radiator hoses to the new double o-ring type. That is a highly recommended bulletin and will reduce a myriad of cooling problems.

With those miles, when was the last time the thermostats were r@r'd? They do become punchy and can intermittently fail (sound familiar)?!

Start with the cap and the pressure test. Not a betting guy, but it sounds like a likely cause.

Denny

 

Do you hear the fan ROARING before or during the overheat? Your clutch fan may be out and that would cause a overheat while towing situation.

Degas bottle cap needs to be replaced. It is a known (cheap, easy) failure point in both the 6.0 and 6.4.

 

Any coolant missing? If t-stats are good, next test would be overflow cap or headgaskets.