Gear Oil, any advantage stepping up to 85w-140?

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Bear80

Bear80

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Did a little searching and it seems everyone sticks with the dino 80w-90 or synthetic 75w-90. I got the jist that synthetic is not worth the jump in price over stuff like Coastal.

However, what about using synthetic 75w-140 or the dino 85w-140? I've usally run the 85w-140 in all my truck axles but what is, if any advantage to using this thicker oil?? I've only heard that this stuff will run hotter since it's thicker and cannot dissipate heat like the thinner stuff. Myth, or not? What's really better for the bearings?

:cheers:
 
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I am running 85/140 right now...cheap stuff too. I change my fluid almost monthly due to my wheeling.
 
Bear80 said:
Did a little searching and it seems everyone sticks with the dino 80w-90 or synthetic 75w-90. I got the jist that synthetic is not worth the jump in price over stuff like Coastal.

However, what about using synthetic 75w-140 or the dino 85w-140? I've usally run the 85w-140 in all my truck axles but what is, if any advantage to using this thicker oil?? I've only heard that this stuff will run hotter since it's thicker and cannot dissipate heat like the thinner stuff. Myth, or not? What's really better for the bearings?

:cheers:
Click to expand...

I drive my Landcruisers fast on long highway drives all the time
in the south and have used the Mobil 1 75-90 in the diffs and transfer for 20 years; no problems.

For about the last 100K miles, I added LUBEGARD Gear additive
to the Mobil 1; it is supposed to decrease heat, cavitation, etc;
no problems with my gears boxes.

I have considered adding some of the heavier weight Mobil 1 next time I change my gear oil to see if it decreases gear whine, although,
I don't have much to start with. It probably is not required;
Mobil 1 synthetic is the best you can buy, IMHO.

For my front axles, which chronically leaks the knuckle moly grease into the front diff, I may stop using synthetic, and instead use
regular gear oil and change it more frequently. It seems to make
more noise when it gets contaminated with grease. Gear oil contaminated with grease foams, a lot, which can theoretically cause increase wear due to the air entrapped in the oil, however, I have
not experienced any problems or increase wear (metal) on the magnet.
 
I suspect "chronic" means you tried replacing the inner seals and it is still leaking? That means you have inner axles out of spec (they won't seal on the inner axle seal). You can get new inner axle shafts on the chronically leaking side, pop in new seals, and fix the problem vs. wasting gear oil quite frequently.

Would pay for itself pretty quickly depending on your current intervals.

gray said:
For my front axles, which chronically leaks the knuckle moly grease into the front diff, I may stop using synthetic, and instead use
regular gear oil and change it more frequently. It seems to make
more noise when it gets contaminated with grease. Gear oil contaminated with grease foams, a lot, which can theoretically cause increase wear due to the air entrapped in the oil
Click to expand...
 
I use 85-140 Valvoline Durablend semi syn in the rear diff. The thicker oil helps muffle any noise from the Aussie in there. Same stuff in the front with the ARB and I change them both once a year (appx 10k miles). I should mention that I live in a very hot climate and it rarely freezes so thick oil doesn't phase me. I run 15w40 in the motor year round.
 
I run 80w-90 almost everywhere with 2 exceptions.

My FJ40 gets 85w-140 in the gearbox. It's quieter and shifts just fine. It gets such poor fuel economy, that I wouldn't notice if it was worse.

In my 80 series, I run Mobil1 75w-90 in the transfer case. That's very hard working fluid, there are only 2 quarts of it, and it seemed like the ideal place to target with a high $$ synthetic.

Everything else gets Coastal 80w-90 that I buy in 5 gal. buckets, and costs about $1 per quart.
 
DanKunz said:
I suspect "chronic" means you tried replacing the inner seals and it is still leaking? That means you have inner axles out of spec (they won't seal on the inner axle seal). You can get new inner axle shafts on the chronically leaking side, pop in new seals, and fix the problem vs. wasting gear oil quite frequently.

Would pay for itself pretty quickly depending on your current intervals.
Click to expand...

I had the front axles redone a few years ago while it was still under warranty on my 1996 FZJ-80 due to the black moly getting into the diff; then it leaked gear oil into the knuckles,
so had it done again, luckily for me, about one week before
the dealer's one year labor warranty ran out.
But still after all this, moly grease is getting into the diff, so, I gave up trying.

This has happened to all my cruisers, so I figured it was a design problem or common defect.

I have tried to not over lube the steering knuckles; my opinion
is that the design leads to grease being forced by the axle seal
ie: heat and pressure builds up in the knuckle, but it has nowhere
to go, except by the seal, so it is forced through.

I have long wondered if some sort of pressure relief or breather valve, like what is on the diffs, could be put in place of the square
threaded plug on top of the knuckles to prevent this???

Either way, it does not seem to have hurt anything.

As I cannot do that level of work myself, it is prohibitively expensive to have dealer do it; something like $1000 in labor, at least.

So, I just change the gear oil when it starts to look like a black milkshake.

G
 
Royal purp 75w140w in my Subaru & LC... Lots of beating the Subaru on the track & lots of miles. The fluid always looks good when I change it. I've never seen the rear diff temp light in the Soob.
 
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