Changing Gear Oil -- Close enough?

[luckyman]

I've had a lot of breakage do to cold weather and not having lite enough oils in Motors, trans, diff in heavy equipment and pickups. Can think of any hot weather failure do to to thin That I've had. I go by the spec but use the lite side when listed.

[Magnum_Willys]

I just completed my gear oil change.
20 minutes start to finish.
Red Line MT-90 75W90 GL4 seems to be exactly what it wanted.

MT-90 GL4   Thats designed for manual transmissions not differentials ?

[Bean Counter]

synthetic oils  and seals dont get along very well, some seals hold up, but, whenever I switched to synthetic, I started getting leaks, and when they start, they dont stop

might be worth researching what oils you have been using and how the recipes have changed over the years, I know that Delo switched up thier recipe with their 15-40 oil, we stopped using delo at work because it is just too dry of an oil, we switched over to a 76/conoco phillips oil. for all the emmisions regulations, oil isnt what it used to be, since most oil for diesels have gone to a low emission formula, they omit zinc, phosporus, lead, and various other lubrication compounds

gear oil on the other hand, as it is not in a crank case, hasnt changed. I would presume that the lower the opperating temperature of a part the higher the viscosity you would want, which might suggest why the lube in the front diff is thinner than the rear diff to compensate for engine heat.

in a crank case, oil needs to be thin to flow, in a cold gear box, oil needs to be thick to stick and provide static lubrication, as a differential or some gear boxes have the gears partially submerged in lube.

the lighter oil in the winter is correct because it compensates for an ambient temperature diference, and being thinner, and colder outside, it takes less to heat and flow properly, compared to using a light oil in the summer, it would be too thin to properly lubricate, whereas a heavier oil will compensate for summer temperatures and provide correct lubrication.

the US Army did a study on motor oil and concluded that motor oil does not break down or otherwise "go bad", however what makes a motor oil "go bad" is contamination with acids, fine particulate matter such as metal wear, and soot, I recently installed an oil bypass filtration system that is supposed to filter oil so finely, it extends the service interval exponentially, to the extent that the company reccomends sending in oil samlles before doing an oil change, as depending on the level of contamination at a normal service interval, it will dictate 1) what is going on in the engine, and 2) whether or not an oil change is really necessary.

oil is pretty interesting

Night Goat The Oil Man! 

[shadowless_nite]

Use regular gear conventional gear oil 75w90 or 80w90. If it has a lsd use the additive. Your wasting the money on synthetic in a toyota differential. There's plenty of old toyotas out there that have been living with conventional fluids, and short of a lsd the diffs have not changed much.  If you want a picture of the barrel they fill your diffs with at toyota dealer I can send you one, it's nothing fancy.

I work on toyotas for a living and this is getting waaaayyyy over thought. Someone let me know when they seen a toyota differential fail because they put 80/90/75w90/80w90 no friction modifier(non lsd) etc etc. Rarely do the toyota diffs go out and if by chance they do it's almost always from neglect or getting beat on wheeling. The ones that go out just because.... Well it happens about as frequent as any other bad stroke of luck.

[thinkingman]

I just completed my gear oil change.
20 minutes start to finish.
Red Line MT-90 75W90 GL4 seems to be exactly what it wanted.

MT-90 GL4   Thats designed for manual transmissions not differentials ?

Correct
I had run the same gear lube in my box as the diffs and transfer case.
There had always been stiffness in really cold environments until it built some heat.
This stuff is dramatically better and the syncros are so much happier. Shifting is completely different even on startup in 20 degree temps.