rgr4475

Lots of conflicting info out there. I know in the WJ's with D30 and D44 it calls for 80w 90 for normal applications and for towing and other heavy duty applications it calls for 75w 140.

I am not towing anything except a dirt bike on a hitch carrier. I live in the North East so I get hot summers and cold winters. I don't really go off road. I can be in a lot of stop and go traffic at times. I have a 2" spacer lift and run 245 65 R17 tires.

Was thinking of running Mopar 75w 140. I was reading things like some small gas mileage can be lost and it could also create more drag. Figured for a lot of stop and go NYC driving the 75w 140 would be better. I dont care about price. Thoughts???

Nick-B

For your conditions and driving I'd go with 75w-140 synthetic. Won't make a bit of difference in mileage (at least in an XJ) and will provide superior lubrication for many years.

dave1123

Most 75W-140 is synthetic and is actually thinner and more slippery than 80W-90 GL5 gear lube. I'm using Valvoline 75W-140 Syn in both my diffs and at 212K miles, they are both wearing properly, no gear tooth galling or bearing whine. I live in the winter wonderland of Syracuse, NY and deliver newspapers 3 days a week in all kinds of weather and it's hard on vehicles because of the stop-and-go all the time. On special editions, I've had 1/2 ton of paper in it. I've also made several long trips on the highway with it.

IDK if the diff lube had anything to do with it, but on a 4 hour trip to Rochester and back, same day, same wind conditions, 90*F air temp, no A/C with all windows down, 70 mph, I got 27 mpg with my 4.0! That's actual fuel usage, not VIC indications. I was stunned! I expected maybe 20. That's with 3 souls on board going out, no cargo, and just me coming back.

rgr4475

Thanks guys. And Dave did you have a 60 mph tailwind?

dave1123

No, but the Thruway is totally flat between Syracuse and Rochester and runs thru the Montezuma National Wildlife Refuge.