Pros/cons with 80W90 GL5 vs 85 or 75W140 GL5?

[aquariuscsm]

Are there any pros or cons when choosing weights for a rear differential gear oil,like 75W90 vs 80W90 vs 75W140 vs 85W140? I`ve often wondered what the best all around rear differential GL5 gear oils are,weight wise,to ensure the longest lasting rear differential.

Is too thick of a rear diff oil a bad thing?

 

[mechtech2]

South Texas residents can use thicker rear end oil than Yankees.

I don't know about drag, but the thicker versions will protect better. Hypoid gears are tough on lube - they all slide a bit.

 

[INDYMAC]

Don't forget about SAE 110. That's what I plan to switch to now that I'm all out of discontinued LE 607 (SAE 90) in all my vehicles. If you prefer a multi-vis synthetic, then AMSOIL SVT 75W110 would be a great choice. I'll continue to use 75W90 synthetic in the transfer case and front diff though, since these components are usually called upon to do their best work without the luxury of a warm-up period.

 

[mikeg5]

Indy, i thought about doing that myself. put nothing but M1 (or any other syn lube) 75w140 in the rear, 75w90 in the tcase and the same for the front diffy. bc like you said they do not get used like the rearend does.. anyone else want to chime in on this? to me it sounds good and logical

 

[aquariuscsm]

Originally Posted By: mechtech2
South Texas residents can use thicker rear end oil than Yankees.

I don't know about drag, but the thicker versions will protect better. Hypoid gears are tough on lube - they all slide a bit.


The part where you mentioned drag is what I`m concerned with. I`d hate for a thick diff fluid to slow my car down. Nissan FSM specs 80W90 GL4. Would 75W90`s be maybe a tiny bit on the thin side? I know the OEM (Pennzoil 80W90) was much thicker when I drained it last year and replaced it with Mobil 1 75W90.

What would be everyone`s choice out of these:
Mobil 1 75W90
Sta Lube 80W90
Pennzoil 80W90
RP 75W90

Those lubes are the ones I can just run to the store and grab conveniently.

 

[INDYMAC]

Of the ones you are interested in, the M1 has shown the best performance on UOA's and AMSOIL's whitepaper that I've seen. If you make a little more effort, you can find a better GL5 though. Remember, just because a multi-vis gear oil (85W140) is labeled as a thicker gear oil, it won't necessarily be much thicker than a 80W90 until the temperatures in the differential require it to be thicker.

 

[mechtech2]

Gear oils are rated at about 150 deg F. They can get there easily, especially in a warm climate.

140 is thick enough that the extra drag should show up in a bit less of economy and power. A trade off of protection vs. internal drag.

 

[mikeg5]

i dont think you will notice much of a difference in synthetic 75w90 vs 75w140.. the syn flow properties are much better.. if you go to a 140 wt i would go synthetic

 

[PT1]

Down South it probably doesn't matter much except for fuel economy vs drag. Up North in colder climate in an exclosed full axle assembly you will want 75w to insure you don't get bearing starvation on cold start. But 80-85w will give you better noise abatement versus 75w. So it is always a trade off between all those variables. Some engineers believe 80w has less shear tendency than 75w and will spec it for that extra safety margin for users who never change diff oil and will sacrifice fuel economy for protection. GM is driven by CAFE & 100k warranty in their grape juice quest. I still change at 50k no matter what and don't vary the manufacturers spec. on oil weight.

If you have ever had a noisy differential caused by poor or incorrect lubrication and the high expense and difficulty of repairing one correctly you will be mindful to make sure you don't run lubricants beyond their recommended limits.

Dana has volumes of information regarding diff testing and when you speak with the test guys they will tell you 3 important things that most people don't realize.

1. 95% of a differential's break-in wear occurs in the first 500-1000 miles.
2. Average life cycle of a differential will almost double if the factory fill lubricant is changed within the first 3000 miles and thereby removing break-in debris.
3. Manufacturer spec.ed viscosity is critical to long life and recommended OCI's should never be extended especially if severe service is encountered.

 

[bruce381]

depends what you want for the best gear protection use the thickest oil that will still flow at lowest temp you live.

140 or 250wt

for lowest "drag" and "moderate" protection go thin or multi grade lowest would be perhaps a 75/90 or so.
bruce

 

[Titan]

75-90 is associated with a whine in one of my Subaru Rear differentials, the other is quiet with the same fluid. Mixing half 75-90 with half 75-140 quietens the noisy one to almost as quiet as the quiet one. If I had 75-110, I would have used it in the noisey one.

I put 75-140 in my Gramp Marquis...and get an average of 26.7 mpg at 70 mph cruising. I just took out half of it and put in half 75-90...again, 75-110 would have been perfect. No change in mpg noted...but, that's not much of a change, so, I wouldn't expect to see any difference.

 

[aquariuscsm]

My car`s rear diff holds about 1 1/2 quarts. I`ve thought about going with 1 quart 75W140 and 1/2 quart 75W90.

 

[Saturn_Fan]

My Nissan pickup holds almost 3 quarts in the rear diff (75w-90) The manual transaxle fluid capacity is almost 3 quarts of 80w-90.