Well.... I think she's fairly well roasted. Was heating up way too much when heading out camping for memorial day so after I felt the fan clutch wasn't doing good enough I got a new one. Did water pump, fan clutch and thermo and flushed system.. Radiator is new, coolant wasn't bad at all but wanted reassurance.

Headed out today and I couldn't get it to cool down. Idling at 220 degrees, light load ~6000lbs doing 50mph and its pegging at 245 and cylinder head temps are through the roof at 280-285. Turned around and came home. Cannot get to cool down. Checked it all, waters flowing, put new thermo and checked it opens all the way before installing.

Started pulling plugs. Some white looking lean, some fine, cylinder 6 covered in oil. Threads and the 'nut', all covered with oil film. The lower porcelain inside the cylinder looked fine, the outside porecelin and boot perfectly fine.

What the H... Has happened??

 

Is it BURNING oil (blue smoke) ?

 

Nope. No oil or coolant loss at all. Nothing as of now but it will run fine, just at 220 degrees in the city.

 

What brand thermostat did you use? What coolant? Can you remove the thermostat and test it on your stove in a pot of water.

 

Two other thoughts occur to me:

Has it ever spewed coolant, and REALLY overheated, or are you relying on a gauge?

And if you ARE relying on a gauge, which one? Physical temp gauge, electric temp gauge, dash, Scangauge on the OBD-II?

 

Sorry for the delay, we are out on the road without the truck. Thermostat tested good in hot water.

Never blown out coolant, using torque to see temps, got to 244. I used two infrared temp guns and both read the exact same as my temp sensor.

 

blown head gasket letting compression enter the cooling system maybe?

 

Where did you take that temperature from?

Can't be head gasket, otherwise, it would puke at some point.

I have to suspect the radiator at this point, use that infrared gun, and check the temp at the input and output of the radiator.

 

couple of things. 1st replace the rad cap had a similar problem some years ago and it was a bad cap. If the plugs are are looking lean get a check on the injector fuel system. Lean running will cause to overheat. Had a problem with a 351 in a f250,injectors were dirty so r&r'd them problem went away. If nothing else run some sea foam thru the fuel tank for a couple of tanks.

The 6.0 has similar water resevoir and the caps have been shown to be weak and not hold pressure. I pressure tested 6-7 before finding a good one for my F350!

 

Cap has been replaced, but I don't have my old one still to test.... Didn't think about that. Radiator came out and it took everything I could give it without even breaking a sweat with a 1" hose and wasn't backing up at all full blast.

I left the following morning with my other truck and didn't tow so its been at home the last week without anything being done yet. I plan to fully diag before pulling a head or anything.

Injectors known to get plugged up? I run good gas with cleaner fairly often.

 

If it was getting hot as the sender unit is saying I would think it would be pushing coolant out or at least filling the coolant reservoir. I'm strongly suspecting that it's just a bad temp sensor and I've had good and bad luck with infrared temp guns, they look at a wider picture of things then the laser is pointed at and can give erroneous readings in a tight engine compartment and if you try a close shot of things the lens heats up and now everything it reads is bogus.

 

People on this forum often talk bad about the temp gauge/sensor. They say it's just a glorified dummy light, and that it reads inaccurately, etc...

I completely disagree. Every car I've ever seen that indicates high temperature has an actual problem.

Torque app, laser thermometer, and a steadily rising dash gauge = yes, you have excessive heat.

Let us know how you fix it.

 

I used two guns right next to the sensor and all three read roughly the same....

I am planning a more advanced diag when I get back to town this coming week.

 

I used two guns right next to the sensor and all three read roughly the same....

I am planning a more advanced diag when I get back to town this coming week.

 

Wasn't doubting your findings so much as giving my 2¢ worth on them. If all the parts you replaced are good and it's getting hot as you're seeing i'm very surprised that it's not puking coolant. The only other suggestion I had was the radiator being plugged with calcium deposits but it doesn't really fit your problem, it's more of a slow progression to hard to keep cool when towing then later going nuclear hot when towing then hot just driving empty.