Thread: 85/ 140 gear oil sooo much better!.

Originally Posted by sumo

about 6mths ago i changed the deefer transfer case , rear diff (salisbury) and front diff from 90 grade gear oil to 85/140 mobil gear lube.

Man! what a difference, noticed it straight away, but was a bit unsure whether it be good or bad in the long term. But after about 15000ks i say its all good, just so much quieter, especially on long highway runs, bugger all noise out of the fransfer box, where as before it had that famous landy scream after a few hrs travelling. i would recomend the heavier grade any day.

cheers Sumo

I'll let a lubrication expert say whether its good or bad in the long term, but that is some pretty psycho stuff - Mobilube HD. It's has the highest KV @ 40 of any Mobil Gear Oil, 328 cSt.

With the amount of diff wear and T/C wear at 305,000 thats likely to exist, I might give it a run, provided:

a) its not deleterious; and
b) my disco ever moves again.

just watch the temperature and speed that you operate the vehicle at as the 85/140 tends to make the box work significantly hotter.

Not so much a problem in the series as they arent real quick but there is the potential due to the generally lower pourability of 85/140 that the outputshaft of the gearbox might suffer increased wear Especially while the tcase is cold.

Originally Posted by Blknight.aus

<snip>
...... but there is the potential due to the generally lower pourability of 85/140 that the outputshaft of the gearbox might suffer increased wear Especially while the tcase is cold.

that's about the only downside I can think of in the t/case.
Experiments have shown that some of the very heavy mineral based diff oils can take minutes to reach critical areas at not very low temps.
There never used to be an official range between SAE 90 and SAE 140, and the differences in actual viscosity can be huge, so some blenders started offering offering 75W-110, which made sense, and so the ranges were split.

SAE 90 ranges from 13.5 to 18.4 cSt @ 100*
SAE 110 ranges from 18.5 to 23.9 cSt @ 100*
SAE 140 ranges from 24 to 32.4 cSt @ 100*


I'm currently running a mix of synthetic 80w-140 and 75w-90 in the t/case.
Interesting that some manufacturers are now offering 'mid weight' gear oils.

In the past, prior to the seals being replaced I just threw in whatever I had on hand spare, anything from the trickest 75w-90 to basic 80-90 EP fluid as it found it's way out fairly quickly.
When the box and case was apart six months ago there was absolutely no wear on the input shaft splines.

Sals rear ends almost demand a 75w/80w-140 in summer when working hard, eg. towing as they run very hot. Rover diffs run significantly cooler and so IMO nothing above an SAE 90 is necessary.

Just to check I'm interpreting this correctly, for an LT230 I should stay with 75-90 and for the Rover diff likewise, but it doesn't matter if I've got 80w-140 or the normal 75w-90?

Originally Posted by Slunnie

Just to check I'm interpreting this correctly, for an LT230 I should stay with 75-90 and for the Rover diff likewise, but it doesn't matter if I've got 80w-140 or the normal 75w-90?

Castrol recommend VMX80 for the LT230

Originally Posted by Brian Hjelm

Castrol recommend VMX80 for the LT230

and they're wrong if they do.


Factory fill these days is a Texaco semi-synthetic 75w-90 GL5
In the past it's been anything from SAE 80EP from -35*C up to 30*C to SAE 90EP from -10*C up to 50*+, so a 75W-90 GL5 covers that nicely.

Generally, you will get better gear protection with a heavier grade oil, (This is from a bloke who's job is blending industrial oils, and has been to seminars and lectures on gear/diff lubrication with some of the brightest in US lube blending) but thicker isn't always better. As with anything, a lot depends on the quality of the lube too.
I wouldn't dump a good 75w-90 in a t/case just to add some 85w-140 whatever. It could be a backward step, and you have to use a bit of common sense.

FWIW, I nearly burnt the skin off my hand one day when I just touched the Sals after a hard run, I should have put a thermometer on it just to see how hot it was, whereas the front diff I could hold my hand on easily.

Originally Posted by Brian Hjelm

Castrol recommend VMX80 for the LT230

No they dont, they recommend EPX 80W90, it clearly says that right here.

I usually put Penrite 80w/90 hypoid gear oil in the transfer and diffs, am i doing the right thing there or not?, It has started to whine a bit. Gearbox i usually put Penrite 75w/80 manual transmission oil, i give the old girl a pretty tough time offroad so usually change transmission oils every 10k and check them weekly. Is there anything i should be doing different?