Overheating while towing under capacity

MICHAEL PARKER

MEMBER
1994 FORD F-150
5.0L
V8
4WD
140,000 MILES

My truck has a 302 engine. Full tow package. Trailer that is being towed weighs (weight from a scale, not guessed at) 3,100 and 3,400 pounds based on load.
Truck overheats only while towing on an incline, no matter how slight. Runs slightly warm while towing on flat ground ground but quickly cools to normal (or below) when running downhill.
Thermostat is new and just had a full coolant flush and fill in which seemed to give a slight (albeit short term) improvement. I have read possible radiator and possible water pump. Where should I start?

3 Replies

STEVE W.

MECHANIC
12,958 POSTS

First thing, use an air nozzle and blow out any crud from the radiator and between it and the AC evaporator. Next go to an auto parts place or even Harbor Freight and get a non contact I/R thermometer. Start the engine and check the temperature at the pump and heater hoses. If the heater hoses start to warm up fast the pump is working. Another quick test that you can do while towing, if it heats up, turn the heat on full hot, watch the temperature gauge, if it starts dropping real quick the pump is working. This is because the heater core is more efficient at heat transfer than the radiator.
Use the thermometer to scan the radiator as well. You are looking for spots that do not warm up as fast or at all compared to the rest of the core. This can show you if the radiator is partly plugged. This should be easy to see when the thermostat opens.

Oh and if you think the thermometer is a bad tool to buy (like $25.00 for the gun version at HF) it is also great to check wheel bearings, brakes, exhaust systems and more. The wheel bearing temps can alert you to bad grease quick.

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Thursday, June 29th, 2017 AT 10:29 PM

MICHAEL PARKER

MEMBER
2 POSTS

As for running the heater while towing we have done it and it dissipates some heat, not a fast reduction, and sometime not enough, but it does show a reduction or at least a slowing in the temperature rising.

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Thursday, June 29th, 2017 AT 10:38 PM

SATURNTECH9

MECHANIC
30,870 POSTS

Just to add to this one I would suspect a bad radiator fan clutch.When the engine is running at normal temp does it sound really loud from the radiator fan moving a ton of air?

If not here is guide to help you replace it

https://www.2carpros.com/articles/fan-clutch-removal

Please let us know what happens, we are interested to see what it is.

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Sunday, July 2nd, 2017 AT 6:47 PM