Full synthetic gear oil recommendations?

[disturban]

Originally Posted By: Pablo
Originally Posted By: disturban
Lower Cold flow properties would also mean less oil on the gears at initial start up? A thicker oil would stick to the gears.

If we was talking about motor oil you would want the cold flow properties but I dont know about gear oil?


No, the opposite. All oils run off and "stickiness" is not a property directly related to viscosity.
I can see some of the logic in that statement however if 75w90 would be better at protecting my gears at initial start up why would the manufacture recommend 80w90 instead of 75w90?

 

[jstutz]

because they know 80w90 will work in almost all conditions. They dont care if it is the best.

 

[Johnny]

I feel one of these coming on.

 

[disturban]

Originally Posted By: jstutz
because they know 80w90 will work in almost all conditions. They dont care if it is the best.

If 80w90 will work in almost all conditions exactly what conditions would it work in that 75w90 would not? I am not trying to be an [censored] here I am just trying to learn. I live in Michigan a state where we have to use the AC and Heater in the same day...lol! We also get 90+ degree summers and -0 degree winters so if something would work better I am open to hearing why.

 

[Pablo]

Because they don't necessarily recommend synthetic and because they live in a different world.

 

[exranger06]

Conventional gear oils are typically 80w-90. I don't think I've ever seen 75w-90 conventional. Synthetics however, usually come in 75w-90, not 80w-90. Now the reason WHY oil companies do this, I have no idea, but they do.

Your vehicle came with conventional from the factory. THAT'S why it recommends 80w-90. If it came with synthetic from the factory, they would recommend 75w-90. Yes, it really is that simple.

 

[PT1]

The big difference I have found is noise abatement. My wifes Lexus RX330 called for 80w90 and I put some 75w90 in it and got an audible whine at freeway speeds. Drained it and filled with 80w90 and no whine. So, that made me a believer to stick with the spec. Since Amsoil makes a syn 80w90...problem solved.

 

[disturban]

Originally Posted By: exranger06
Conventional gear oils are typically 80w-90. I don't think I've ever seen 75w-90 conventional. Synthetics however, usually come in 75w-90, not 80w-90. Now the reason WHY oil companies do this, I have no idea, but they do.

Your vehicle came with conventional from the factory. THAT'S why it recommends 80w-90. If it came with synthetic from the factory, they would recommend 75w-90. Yes, it really is that simple.
That is a very valid point! I think that is right on the money!!! Very good info...now if I switch to synthetic for my diffs how long can I run it before I need to change them again? With conventional it says 30k

 

[PT1]

Originally Posted By: disturban
Originally Posted By: exranger06
Conventional gear oils are typically 80w-90. I don't think I've ever seen 75w-90 conventional. Synthetics however, usually come in 75w-90, not 80w-90. Now the reason WHY oil companies do this, I have no idea, but they do.

Your vehicle came with conventional from the factory. THAT'S why it recommends 80w-90. If it came with synthetic from the factory, they would recommend 75w-90. Yes, it really is that simple.
That is a very valid point! I think that is right on the money!!! Very good info...now if I switch to synthetic for my diffs how long can I run it before I need to change them again? With conventional it says 30k


You can run the Amsoil 80w90 at least twice the factory recommended change or 100,000 miles whichever is less. If you tow run it 50,000. So in reality it is cheaper than conventional.

 

[Pablo]

Originally Posted By: PT1
The big difference I have found is noise abatement. My wifes Lexus RX330 called for 80w90 and I put some 75w90 in it and got an audible whine at freeway speeds. Drained it and filled with 80w90 and no whine. So, that made me a believer to stick with the spec. Since Amsoil makes a syn 80w90...problem solved.

Yes - but that had nothing to do with the 75W vs 80W and more do with the 100°C viscosity and other lube characteristics.

 

[Johnny]

disturban, look at it this way. A 80W-90 is about the same viscosity as a 20W-40 - 20W-50 motor oil, where the 75W-90 is about the same viscosity as a 10W-40 motor. Now since the 75W-90's are synthetics, they flow better in extreme cold weather, and under extreme heat they protect better. That is why most over the road rigs run a synthetic 75W-140. It also help with fuel mileage some. Here is a viscosity chart so you can compare motor oils Vs gear oils.

http://www.bobistheoilguy.com/index.php?option=com_content&view=article&id=48&Itemid=55

 

[PT1]

Originally Posted By: Pablo
Originally Posted By: PT1
The big difference I have found is noise abatement. My wifes Lexus RX330 called for 80w90 and I put some 75w90 in it and got an audible whine at freeway speeds. Drained it and filled with 80w90 and no whine. So, that made me a believer to stick with the spec. Since Amsoil makes a syn 80w90...problem solved.

Yes - but that had nothing to do with the 75W vs 80W and more do with the 100°C viscosity and other lube characteristics.


You are probably correct but it worked...so that is my story and I'm sticking to it...

 

[INDYMAC]

Valvoline makes a conventional gear oil with a 75W-90 GL5 labeling. I believe Castrol does too. So I'm not quite sure what the earlier reasoning/discussion for a 80W-90 manufacturer recommendation was all about. I say labeling, because the oversight on gear oil standards and compliance seems rather loose. AMSOIL is aware of this (see white paper on testing gear oils). Manufacturers are aware of it too. They seem to want to have their customers error on the side of high temperature and heavy load capabilities wrt to gear oils, so you'll often see SAE90 or 80W-90 recommended as a result. They have a better chance of staying in grade at high temperatures than your average OTC 75W-90 GL5. Cold flow properties are not as important to a manufacturer that has to be concerned about warranty replacement.

 

[PT1]

Valvoline also makes 80w90 Durablend. $6.99 at autozone.

 

[jstutz]

Here is the best i can do for you. Below is the specs for M1 75w90 and mobil 80w90. Notice the cold temp viscosities. I used 0F becuase it is your coldest winter(about). you can see that the 75w90 is mush more fluid at cold temps. Being that 75w90s are generally synthetics they probably offer more heat shearing protection. i have read about this alot lately trying to figure out if I could go thicker in my trucks as they are all over 180k miles and i live in a climate that never gets below 15F. Usually about 20 is all we see. i have read many people notice noisy rearends with the M1. No idea why this is but alot of people notice it and dont like it. Amsoil did a differential oil test(i know amsoil marketing) but it looked pretty reliable. It shows that just becuase something is synthetic it dont necessarily do better under some conditions. in general the synthetics did perform better than the regulars. Hope this was some help. Here is the link.

http://www.amsoil.com/lit/g2457.pdf





mobil 1 75w90
cSt @ -18ºC 1652 (0 deg F)
cSt @ 40ºC 106 (104F)
cst @ 100ºC 15.2 (112F)

Mobil HD 80w90
cSt @ -18ºC 3397
cSt @ 40ºC 139
cSt @ 100ºC 14.5