tow truck THIKS its overheating

Have you plugged a code reader into it that can read what the computer thinks the temperature is? It could be a bad gage or it could be the temperature sender. Use the code reader to check temp with the engine cold and still off and see if that makes sense.

What have you done to diagnose the problem?
You threw out a generic open ended question,with no context.
Electrons are cheap, there is no character count so please restate your question with specific symptoms and attempted remedies. Right now you have posters throwing **** on the wall to see what sticks.

The dash board says it's overheating...why do you believe it's not overheating?

It wouldn't be unusual for a marginal coolant system to be fine under light load but pull an 8000lb trailer up a steep grade in 110F, it struggles to keep the engine cool.

Running light on flat ground, it may only take 60-70hp to run at freeway speeds and even if the fan clutch doesn't kick in, there is a 60-70mph breeze blowing the heat away.

Change that to pulling an 8000lb trailer up a steep grade doing 20mph, you might be pulling 3 times the power and the breeze is pulling away far less heat at 20mph.

Too many questions to do anything other than speculate. To help:
- Provide the truck specs. (engine, tow rating, payload, year, etc...)
- Provide the trailer specs (model, GVWR, any unusual modifications)
- Provide the conditions where you experience the issue (Speed, grades, temps, etc...)

Is your F150 an EcoBoost or the 5.0?

It is probably going into 'limp mode' when it does that. This reduces power, but keeps you moving and it won't necessarily steam or spit out coolant from the system, even running that hot.

To get the gauge to move, you usually have to have gotten it over 250* coolant temps.

If it's the Eco, you are likely using a lot of boost to maintain speed and while the power is there, the cooling isn't when it's over 10psi of boost.

Could also be the water pump. I think the OEM has plastic impeller in it and it could have broken some of the fins..

Only guessing here. I have to watch the boost level and temps when working my 13 Eco. I monitor with a ODB2 plug in and phone app. Gives me actual temps and the boost psi among a ton of other sensor temps and things..

Good luck! Mitch

flathead92 wrote:
our 2011 f 150 under load red lines and overheating warning light comes on BUT it is not over heating???? Ideas ???

Your temperature gauge red lines?
If that is the case test/replace sensor, otherwise figure out why it is overheating.

bad sensor?

Head gasket?

How do you know it is not over the heat limit set by the factory? Not sure it has to blow steam to confirm over temperature. Does it cool down if you slow down or let it idle?

Could it be the transmission overheating? Do you hear the fan clutch engage?

Is this the first time towing?

I wish it was that easy. like I said it Thinks its overheating under load works fine not hooked up to TT. Even Ford is like ????

Plugged radiator?
Or a solid mass of dead bugs etc blocking airflow through the rad. The AC condenser is in front of the rad. If any of this is blocked, temperature could climb under load.
Clutch fan malfunction?