Who is running 85-140 in their rear axle? I have Valveline Dura blend 85-140 in my 99 dodge and ran regular Valveline 85-140 in my 31 year old Chevy K20 for last 20 yearsI called Valveline tech to see what % of friction modifyer they put in their gear oil marked "limited slip" because im going to change my oil. The tech guy had a interesting comment about gear oil weights. Ha !

In my '06 heavier gear oil is called for, for contenuious towing. It seems like personal preference to me.

Rick,You gotta share!!!! But weights and such get funny. Lots of differences between straight weights and modifieds (like the 85-140). It also depends on what you are doing. heavy weights, for no reason, can make a large impact on efficiency. So not only are you using more hp than necessary (therefore less mpg) but you are also increasing the temp of the fluid.The ultimate goal is to provide a layer of oil (between the teeth) that won't extrude under the pressure, and allow metal to metal contact. The hypoid gear set has a LOT of shear and is heck on the long chain hydrocarbons. The fluid also provides the cooling, so it needs to maintain throughout a large temperature range. (It would be easier if we were just lubricating all the bearings..... they are EASY) some engineer somewhere just HAD to take that rotary motion and turn it 90 to everything. and then said "hey let's do gear reduction here too!" and then someone said "lets make this thing quiet!" Give me large straight cut gears and ear plugs any day!!!Hag

I use 80W-90 typically in my truck since heavy hauling and trailer towing is limited and not done every day. But thinking of this its time to check the rear diff again.

I just recently bumper pulled over 10g's running amsoil 80w90 with 3.55's, so that was a reasonable haul...well over 2000 miles...not much wear in my maghytec rear to speak of. im not necessarily convinced that heavier means greater protection.I'm even running 10w30 rotella in my rig right now...

I run 80w 90 conventional front and 75-140 valvoline pure synthetic rear, its expensive but so is going through a rear end

I just recently bumper pulled over 10g's running amsoil 80w90 with 3.55's, so that was a reasonable haul...well over 2000 miles...not much wear in my maghytec rear to speak of. im not necessarily convinced that heavier means greater protection.

I'm even running 10w30 rotella in my rig right now...

I've even consider that myself for the winter time... Just never did it.