I think that's the best oil and I also use it. It's thick, so your mileage may be by .5 gal less, but overall, use it, all serious offroaders I know use it. I have Lucas mineral 85w 140 in mine, best there is.

Not Mobil1 Synthetic?

This is an interesting topic, regarding mineral vs synthetic for the use of gear lubes.
I fully understood mineral vs synthetic in the use of engines, but who would have thought synthetic is recommended for differentials.

From what I have gathered so far mineral would be fine to use and in fact it is what a lot of members use.
I spent a whole day searching for lube recommendation from different companies in Australia (Shell, Penrite, Gulf Western, Valvoline, Castrol etc....), and every single one of them recommended Synthetic 80W-140 front and rear. I guess the reasons synthetic is recommended is the better cold weather flow and also providing better fuel economy.

It turns out my wife works 2 blocks away from Gulf Western Warehouse in Clontarf (north Brisbane) and the 4L ULTRA CLEAR GEAR OIL DIFF LUBE LS 80W140 is only $29.79. This is cheaper than the mineral stuff from Super Cheap / Repco which is at least $40.

I will go with the full synthetic Gulf Western purely because it's cheaper than the mineral I buy from retail stores, and will most likely provide better efficiency.

http://www.gulfwestern.com.au/product/u ... ls-80w140/


KJ75

Not Mobil1 Synthetic?

Finally got around doing the front and rear diffs, as the old lube has done over 32000km (it was still nice and clean like honey).

Ended up using Synthetic 85W-140 as I got it cheap from lube outlet in Australia.
Jeep is nice and quiet and no leaks observed.
According to the Jeep manual, it is recommended to change diff fluid every 20000km, but I might let the synthetic go a bit longer.

I thought synthetic oils took longer to break down, am I wrong ?
The oil previously used was also synthetic, and looked very nice and clean (although the Jeep never did any offroad).

What would be a good interval to change synthetic diff oil, considering the manual states 20000km when used to tow or offroad ?

I work for a GM dealership. GM actually recommended switching to a synthetic 75w90 gear oil to cut down on warranty repairs on there HD trucks back in 2001. They left the factory with 80w90 mineral oil. If mineral oil is better, than they should not have told the dealer to change the oil on them to save the company warranty costs.

I work for a GM dealership. GM actually recommended switching to a synthetic 75w90 gear oil to cut down on warranty repairs on there HD trucks back in 2001. They left the factory with 80w90 mineral oil. If mineral oil is better, than they should not have told the dealer to change the oil on them to save the company warranty costs.

The preload they set on the side bearings was high enough that the mineral oil did not lubricate effectively. Off roaders around here use mineral oil because it is cheaper. They change it more when it gets contaminated with water and mud, or break something.