Gear Oil for Diffs & Transfer case

[JBT]

Hi guys. Newbie here. Learned so much from the engine oil forums but I'm less knowledgeable on gear oils so I have a few questions.

The gear oils in my Toyota Fortuner (Mid-size SUV. I think only available in Asia and Aussie) is due for change in a few weeks. The manual specifies the following gear oils:
Transfer case - 75W-90 API GL-5
Front Diff- 75W-90 API GL-5
Rear Diff - Hypoid gear oil 90 API GL-5

1. Most of the oils I see are 80W-90. I shouldn't have any problems using them, right?
2. I have not found any monograde 90 gear oil for the rear diff yet. Is it ok to use the 80W-90 on it?
3. Do all GL-5 rated gear oils automatically qualify as EP or good for use on hypoid gears?

 

[HTSS_TR]

I would stay with 75W-90 gear oil which synthetic oil, it should be available at Toyota dealers. If you can not find 75W-90 then 80W-90 can be used but with shorter change interval because most 80W-90 is not fully synthetic gear oil like 75W-90. For the rear differential you can use 80W-90 but it must be Hypoid gear oil.

 

[unDummy]

As long as it is a full synthetic, you can use any GL5 gear oil grade. Your weather conditions don't really require the 75w cold flow.

 

[Rob_Roy]

I would not hesitate to use a 80w90 GL5 gear lube in those three compartments.

 

[MaximaGuy]

If you get hold of an Amsoil dealer there then you should try 75W110. I have that on my Highlander (both diff and x-case) and the drivetrain is so quiet. I am sold onto Amsoil Gear Fluids.

75W110 should work just fine in Asian climates.

 

[widman]

75W-90 is not necessarily synthetic. Most aren't. But you should be able to find them.

But in those compartments you shouldn't have a problem

 

[JBT]

Most of the ones I've seen are 80W-90 - Mobil, Shell, Caltex (Chevron). The only 75W-90 I've seen so far was Mobil's synthetic gear lube. All GL-5s.

Thanks for the inputs.

 

[JBT]

I'm planning on using fully synthetic gear oil this time for the diffs and transfer case and also fully-synthetic ATF. I'm quite sure that the gear oil and ATF that Toyota put in is just the regular non-synthetics. My vehicle has 80,000 km on it. Last gear oil and ATF changed at 40,000 km.

I've read some posts about some high mileage engines suddenly getting leak problems upon switching to fully synthetic oils after years of using conventional oils. I believe due to synthetics dislodging large chunks of contaminants from seals.

Does this problem also occur in diffs, transfer cases and transmissions? Or will a straight switch to synthetics be fine?

 

[Unleashedbeast]

Originally Posted By: MaximaGuy
If you get hold of an Amsoil dealer there then you should try 75W110. I have that on my Highlander (both diff and x-case) and the drivetrain is so quiet. I am sold onto Amsoil Gear Fluids.

75W110 should work just fine in Asian climates.


I agree, Amsoil's severe gear is awesome stuff! I use it in my Mustang as well, gears are silent. I even use the 75W-110 instead of the recommended 75W-140.

 

[JBT]

I'm planning on using fully synthetic gear oil this time for the diffs and transfer case and also fully-synthetic ATF. I'm quite sure that the gear oil and ATF that Toyota put in is just the regular non-synthetics. My vehicle has 80,000 km on it. Last gear oil and ATF changed at 40,000 km.

I've read some posts about some high mileage engines suddenly getting leak problems upon switching to fully synthetic oils after years of using conventional oils. I believe this is due to the fully synthetic oil dislodging large chunks of contaminants from seals.

Does this problem also occur in diffs, transfer cases and transmissions? Or will a straight switch to synthetics be fine?