Need a diagnosis.

[dogonenuts]

I have a 2005 F250 diesel. I have noted for a year or so only when towing an 8000 lb boat/trailer that at times when going 55-75 mph I will hear what sounds like a fan come on and the engine temp will temporarily go up near the high range, but not to it. I note some loss of power even if I rev the engine. After as much as 30 seconds the fan noise goes off and normal power returns. It seems to do this more in hot weather. It has never done it when not towing. I also, immediately after my last service that I was short about 1.5 gallons of radiator fluid. I have not noticed any white smoke and do not have any radiator fluid collection in my garage.

I am the original owner and have 63k miles on it. Just had the tranny flushed thinking this might have something to do with it, but it made no difference.

Any ideas?

thank,

Nuts

[rentstdi]

I have noticed my fan turns on more often with the a/c turned on. Even if you have the winshield defroster on the a/c is on... Also if the its really hot out and the air intake temps go to above 120 I have noticed that it turns on the fan clutch also. You might have an issue though if you are loosing coolant and your temps go in the Higher normal range.

[dogonenuts]

Nonmechanic here.

[PowerstrokeTech82787]

Plugged oil cooler
Cracked EGR cooler (youd see white smoke steam rather billowing out the exhaust)
Bad head gaskets

Possible to have a bad water pump/front cover.

[forddieseldoctor]

You have high engine temp. Oil or coolant temp. When the temps get high enough the computer will turn the fan on and if it still keeps climbing it will derate the engine to get you to slow down.