I came back over the pass in Mount Eagle TN the other day. I was pulling the 5er, (25,500 GCVW +/-) outside temp at 85. sign says it's 6% grade for 4 miles. I measured 228 degrees on the oil, a little lower on the coolant and 195 degrees tranny temp. The fan did not come on. On the way up it did not come on either. Does anyone know what temp it is supposed to come on at? I hate to pay to get it tested when there is nothing wrong with it. Truck ran fine both times, it just seems like it was hot enough to use the fan.

 

Stan, I think if you add 100 degrees to your temperatures you posted it would seen reasonable.

 

Thanks, just a small brain cramp there. I fixed them.

 

If I remember right mine would come on around 220 degrees coolant temp. Not sure though, that was a few years ago.

 

I have decided it is a variety of factors that influence when the fan comes on. We just back from a 3200 mile trip. EVERY time I would drive up from Lake Tahoe to the condo where we were staying the fan would come on when the oil temp hit 218. However, that climb was at slow speeds (35-40) in 90* weather. When we went from there to Las Vegas, we pulled several long grades and the oil temp would hit 220-222. That was in 110* weather but at 65-70 and the fan never came on.

Based on that experience, I believe the ECU is weighing several factors to determine when (or not) to engage the fan, rather than a set temp.