Coolant Temp Rising While Towing
 

I have a 2002 F150 SuperCrew with the 4.6 and whatever the lamest rearend gear ratio is. 108k mi on the clock.

Lately, when towing for extended periods with the AC running, I notice the coolant temp gauge rising to about 3/4 of the way to the hot mark. It usually hangs around 1/2 way under regular conditions. It seems to just do it on the longer trips (20+ miles) on the highway between 60 and 65 mph. I'm just running regular A/C, not max. If I turn the AC off or turn the vent on and turn the temp hotter, the engine cools back down.

Any suggestions on what I can do to prevent this? Would installing another fan help? It's never overheated, but I've never given it the opportunity to see if it does. All fluids are at the right level and nothing leaks.

I never had this issue towing my smaller boat (right around 2k lbs), but since I began towing this one (just under 5k lbs), the issue has come up.

If u don't have the dual core radiator that's your problem most parts store keep the tow radiator in stock and with that it want get warm

With that many miles, the radiator may need cleaning/replacing, the thermostat may not be opening fully, and the water pump impeller may have eroded.

The thermostat maintains a constant engine temperature by allowing some of the pumped coolant to go thru the radiator. It is normally never fully open. Once it is fully open, it can no longer control the temperature. That is when you see the temperature gauge rise above normal. You add cooling capacity by turning off the A/C and turning on the heater.

So if your cooling system is no longer able to provide enough cooling when pulling the boat, you need to figure out why.