day before yesterday i was towing my 10K trailer it was really hot like 105 degrees up hill and all of a sudden this loud burrr started it sounded like a huge fan or something kicking into gear. but i didn;t think these truck anything like that. the engine heat got up around 200 when it would kick on then it would go off when it got back to about 190. the tranny temp stayed at 180 the whole time egts peaked at 1300. for a few seconds. any ideas?

 

It sounds like the Thermostatic Controled Fan Clutch was operating normally.
When it kicks in, it makes quite a roar, doesn't it?

Ed

 

Just like Shovelhead said, it was the fan clutch. Sounds like a 747 taking off from under the hood!

 

Next time that happens take a look at the water temp, then when the noise stops look again and see if the temp has dropped. If it has dropped, then that is your clue that the noise you are hearing is the fan cutting in and out.

 

First time mine did it I almost filled my drawers... thought I killed a Cummins