I have a 2017 Coachman Leprechaun RV, built on a E350 2016 V10 chasis with less than 38k miles. I have owned it for 3 year now and have never had any problems with it. Last week I drove from Bakerfield, CA to Barstow, CA and about 40 miles before Barstow the Overtemperature light went on. Engine was running well and there was no lack off willingness to accelerate. I cranked up the heat inside and slowed down to 50 mph. Both got the tempertature to just about normal. I stopped at the next rest area and checked the engine and coolant. There was no coolant leak, color of the coolant was orangy, you could see that coolent came into the reswervoir and the reservoir showed it was just a bit above max fill level. After 15 min of cool down, I started again driving twards Barstow. As soon as I got above 55, temerature started to climb again, so I drove slowly to Barstow. There I went to a truck service and they started diagnosing the problem. They confimred the engine was running well, no water pump grinding noise etc. They suspected the thermostat, which had to be ordered for the next day. Friday they replaced the thermostat. Apparently it was stuck in the open position. A quick test run showed that the engine was still overheating. So they thought it might be the water pump or the fan clutch. There was no water pump available in town but a fan clutch. When they disassempled the fan clutch they also removed the water pump to inspect it. They frest the water pump was in good working order and replaced the fan clutch. A test drive still showed overheating. At that point they said tit could be a crack in the engine block or a bad cathalytic converter or somethiung else. They didn't know what next to do and suggested a Ford service station 80 miles away, costing me more then 800$ just to get it towed.
Any suggestions what might be the problem and how to proceed?

 

Does it ever actually puke coolant?

Find one of those point-and-shoot infrared thermometers and next time it supposedly is overheating, check the temperature at the thermostat housing. Check a few other locations, like top/bottom/left/right side of the radiator and report back. Also, if possible get the PCM scanned to see what the actual coolant temperature is.

This information might tell us if it's actually overheating, and if it is, if the radiator is clogged or flowing correctly.

You could have a bad temperature sensor, or the cooling system needs to be burped. Did you have the coolant replaced recently?

 

The scanner reported up to 249F when the issue happened the first time. Didn't have a IR thermometer to check on the engine block. After the thermostat and fan clutch got replaced new coolant was added and motor burped. Still shows overheating.

 

Did they replace the thermostat with a genuine MotorCraft one? I read where someone had 2 or 3 aftermarket thermostats put in and finally put in a motorcraft one and that solved the overheating...he also was told he had a cracked bock or blown head gasket (which he didn't)

Also check for collapsed hose , suction may suck it closed. The clutch fan should sound like a jet engine when it kicks in, Does it?

 

The thermostat was a NAPA part. Fan wasn't making that much noise.

 

Yeah, if the temp is really at 249, that clutch fan should be roaring based on the heat from the radiator. Which leads me back to a clogged radiator.

On edit: or a bad temp sensor, or PCM.