Hi everyone! I have 2015 f350 SRW crew cab, long bed with 160k on it. The truck used to be an oil field truck..or something like that. I live in the high rockies, and to go anywhere I drive over Vail Pass and the Eisenhower tunnel about 11000ft of elevation. I tow a travel trailer with GVWR of 10k. When I'm driving around the temp gauge stays very slightly to the left of the center mark. When I have the trailer everything seems fine in the beginning, and then the arrow jumps to 3/4 very quickly, fan kicks in temperature goes down, then goes back up to 3/4 etc. I found a few threads of the people having the same issue, and I know that many people are saying it's normal, but I'm convinced it's not. I found thing thread on the forum that describes the same issue, and it turned out the guy had crack in the radiator: https://www.ford-trucks.com/forums/1...-question.html . There are couple more on the web, but non of them gets to an answer/solution. Yesterday I drove the truck up Vail Pass empty, and I was keeping it under boost, going pretty fast, the arrow started jumping again. It's an XL, so I don't have all the fancy gauges, ended up getting ForScan, oil temp goes to 242, ECT was around 223. Also I went camping past Denver towing on flat ground and the arrow still goes up and down, while staying slightly to the right of the middle most of the time.

It usually takes a few minutes of high boots, and then arrow jumps, which made me think it has something to do with the secondary cooling system.
-The first thing I did was to clean the radiators. Then I replaced the two thermostats on the secondary. Made no difference.
-Red about the expansion tanks cap issues, and replaced those, still no difference.
-It looks like the serpentine belt broke sometime before I bought the truck, there were some left overs around the pulleys, which makes me wonder about the water pumps, but I found that they usually make the trucks heat up at low speeds rather than high speeds. The hoses are pretty firm, I would say normal.
-Another thing I'm wondering about is plugged EGR cooler, but then I should get a check engine light?
-Fan clutch has resistance, and I can definitely hear it when it kicks in, but is it possible that it doesn't engage early enough to keep the temperature down?
-It also has hand ranch bumper, is it possible that it restricts the airflow(don't belie so)?
-As I mentioned the the other thread the guy had the same issue, and found a crack in his radiator. I don't see any cracks, what other places should I look for coolant leaks? ( https://www.ford-trucks.com/forums/1...-question.html )
-What temperatures, voltages etc should I monitor with ForScan to track down the issue?

I would really really appreciate your help as this is getting frustrating. I am also planning a long road trip an want to fix it, before I hit the road.

Thank you!!!

 

Truthfully I see nothing wrong here.

As long as you degas bottle is where t should be then the truck is fine.

Towing 16K over vail and Eisenhower or Monach I will run 3/4 on the temp guage.

Clutch kicks on high at 220F water temps. I can hit 248 on the oil temps. All normal for the 6.7.

 

Even with 242 oil temp on an unloaded truck?

I know that number is within spec but why is it that high running unloaded?

You never mentioned what your secondary coolant temp was running. I don't watch mine very often and don't know what is normal. It generally stays under 100F running around town with a light load.

 

My secondary runs 115 to 130F.

 

I jave a 2018 F450, it runs thst hot, and just like yours at about 240 the fan kicks on and it cools down very quickly.
I jave seen the ssme temps loaded or empty.
Ambient temps seem more to make a bigger difference than load.

 

I see temperatures like that when pulling my 11K trailer over the mountain passes. Unloaded, it's nothing like that.

 

I haven't checked the temperatures when it's unloaded, just know that the temp gauge still jumps. Talked to a friend of mine who's a semi truck driver. He mentioned that this happens to semi trucks, and that it's always the radiator. Washing it while it's on the truck never works. It needs to be taken off and power washed from the back/engine side. He said that the stuff that gets in there is like cement. Considering my truck was an oil filed truck, it seems like a reasonable argument. I ended up ordering both the primary and secondary CSF radiators. Both were under $500, if this fixes it I'll be very happy. I'll keep you guys posted. Thanks for all the advice.

 

It could also be a bad temperature sensor. You need to get a inferred temperature reader just to see exactly how hot the water really is.