Under what weight and terrain conditions do you guys figure it makes sense to switch from 75w-90 gear lube to the 75w-140 weight? My trailer is not all that heavy, 11,700lbs gvw, and I doubt we will be loaded much above 10klbs typically, but we will be towing in the Rockies in the heat of the summer. Any ideas?

TC

I have run the heavier lube in mine from the 2nd change at 1500 miles. I recently change it at 35k, and it looked almost like it came out of the bottle (synthetic lube - Amsoil). My towing conditions are pretty severe, so I need the protection. If I were you, I would run it, as unless you live where it is really cold, I can't see any down side.

Thanks, Tom,

I decided to go ahead and make the change. I have Mobil 1 in there now. I bought 4 qts of Redline 75w/140 four $6.11/qt. Too good to pass up. Most of my towing is going to be in high heat and mountains. Seems like a little more protection couldn't hurt anything.

TC

Thanks, Tom,

I decided to go ahead and make the change. I have Mobil 1 in there now. I bought 4 qts of Redline 75w/140 four $6.11/qt. Too good to pass up. Most of my towing is going to be in high heat and mountains. Seems like a little more protection couldn't hurt anything.

TC

You should always use 85w-140 (or the like) for heavy towing in hot weather. You should change axle fluid too every 12 to 15,000 miles too in heavy towing synthetic or not because there is on "filter" back there. I have used sythetic in engines for 15 years but I do not use it in axles or trannies unless I need better low temp performance.