I recently bought a 2006 F250 Super Duty 6.0 to haul a 24' cargo trailer 3000 miles across country. The trailer weighs a total of 10,000 lbs.

Before my excursion, a menacing wrench light kept appearing and disappearing on my dash that lead me down a rabbit hole of future snowballing problems. After doing some research, I decided before my trip it might be a good idea to have the coolant flushed and the oil changed. I took the truck to Firestone and after working on it for about 2 hours, they informed me that they were having some trouble with air pockets and it should be done soon. About 10 minutes after that, they called and asked if my heater was working before I brought it in, to which I replied yes. They later called saying the truck was ready for pick up. Right before I left on my journey, I noticed a huge puddle of coolant under the truck. It was spewing from the coolant cap. Because I was under a time crunch, I brushed it off to my own negligence in replacing the coolant cap earlier when I had checked the coolant level. About an hour into my trip, my truck flashed a warning to check engine temperature. The temperature gauge spiked, but in a few minutes returned to a normal temperature. I checked the coolant and everything appeared normal. I checked my mobile code reader app to verify my coolant temperatures, which were normal. This pattern continued for the trip, with varying time in between temperature warnings. Sometimes, it would be 10 miles between warnings, other times 600 miles. I figured this was probably air in the coolant system that Firestone failed to remove correctly after doing the coolant flush. During a particularly annoying stretch of 10 mile warning lights, I called a mechanic to bleed the cooling system of air. The mechanic instantly told me that I had blown a head gasket. This surprised me as I had no other symptoms of a blown head gasket. I wasn't losing any coolant, there wasn't white smoke blowing from my exhaust, and there was no mixing of fluids between my coolant and oil.

I need to resolve this issue, but before a mechanic tells me I need to throw thousands of dollars into my truck (being active duty military, I don't have that kind of cash laying around) I was hoping I could get some feedback from this forum on the possible mechanical problems I'm dealing with. My gut feeling says that if it's a blown head gasket, I wouldn't have been able to go for such long stretches without any problems and the overheating problems wouldn't be so inconsistent.

 

Did you find a OBD code for the original wrench light? Obviously an issue to allow this to prompt.
I'd start with the easy first, replacing the thermostat. Did they remove when flushing or work thru it instead? Maybe debris allowed it to stick if left in during the flush?
If not the issue, I'd measure the coolant system pressure Next. A blown head gasket will elevate that pressure and allow the cap to leak. I think your stock cap allows for about 16psi when guessing.
If your not loosing coolant, I'd not dig into the egr cooler just yet.
Got to you tube and view the videos on coolant pressure checking.
I might agree with the head gasket theory until proven otherwise.

 

What is the temperature actually getting to? Can you get actual temps from your code reader? The stock guage is a glorified idiot light.

Usually a spike in temperature indicates an air pocket has passed the sensor. The system in the 6.0 is self-bleeding so the likelyhood of an air pocket left from the flushing is pretty unlikely.

When I blew the headgasket in my old 5.0 Mustang it did the same thing. Would be fine driving around town, but take it on a trip longer than 60-minutes on the highway and suddenly the guage would spike. I'd pull over and find a bunch of coolant missing. Go about another hour and it would do it again.

Sorry man, sure sounds like a headgasket. Probably why the previous owner was selling it?

 

Get the truck to temp, then carefully release the degas pressure. Drive some more, try not to raise coolant temps. Vent the cap again, no pressure built up is what you want. If you get some pressure, head gaskets are most likely.