The exact viscosity of gear lube is not all critical, just make sure whatever gear lube viscosity you choose is rated GL-5 which is required for axles. For rougher uses including towing, stick with a higher number viscosity. For milder uses and colder climates, a lower viscosity is fine. are all fine viscosities depending on how you drive it. 75W-90 is the factory recommendation but that recommendation goes to a higher viscosity if you tow or do much really difficult offroading. One thing I did find is that its not reccomended to run an auto locker like the spartan in a D30 since the xj does not have manual lock-out hubs. I read some good reviews and they arent too expensive. 'The exact viscosity of gear lube is not nearly as critical in your axles as it is in your engine. Ive been tossing around the idea of throwing a spartan locker in my D30. Here is a qoute from another member on oil weights Synthetic is fine and you probably wouldnt notice a difference but dino is cheaper and you replace everytime you crack the case which in my case is about every 5k miles or 1 year.Īlso I run 75w - 90 as it is factory recommended & i do not really stress my diffs at all. There are multiple tests that confirm this which is more important in an offroad vehicle that has different stress and service intervals then a truck driving highway across the country. The oil will be cooler but the gears stay hotter.

I wasnt saying synthetic was bad but in the differentials it does not displace heat as well as dino oil.

Xj cherokee dana 35 spartan locker