Originally Posted by dmac
Yes - I have driven long distances with the OD off. I have then tried OD on, and actually found the temp to drop a little. My tranny temp is also dependant on outside air temperature. Unless the tranny is hunting due to a long slight grade or headwinds, I advise OD on.
However, on the steep grades I was referring to... the truck never gets to 4rth, or even 3rd gear. It's in 1st or 2nd going up the steep incline of I-70 approaching the big tunnel in Colorado or going over the high passes. It heats up fast, rising to 210-215 (with outside temperatures of ~85). I stop at turnouts and let it idle to cool down before proceeding. It takes longer to cool down (15 min) than it takes to heat up (5 min).
Also, wind direction seems to play a huge role in gas mileage. With a moderate headwind (10-20 mph) I got 11.5 mpg, but with a tailwind I got 14 mpg.
I never tow with the OD on, and the rtuck runs cooler with the OD off. The tranny will climb in temp if I leave the OD on. I have found that once I let it get hot it takes a while to cool. I do not pull on the grades you do. I may start soon , I just returned from a meeting in which I was offered a postion in Denver. The next truck will be a 250.