Mobil1 75w-90 vs brandx 75w-85

[oil pan 4]

Brandx is whatever I can get, like at all, 75w-85 is kinda boutique.
I have my beater 1999 dodge Dakota 5.2L with 9.25'' rear, just replaced the pinion seal last week. Still leaking a tiny bit around the cover gasket, if there is one. So that will be coming off.
I was going to filler up with Mobil1 75w-90 because:
I already have it, mobil1 75w-90.
It's relatively cheap.
M1 has great, if not the best oxidation stability.
M1 doesn't have the best shear stability so I'll just top off once a year with 140wt.
The truck normally doesn't get driven a lot, well until I splattered that deer with my wife's car...
Only disadvantage 75w-90 might have it is gets thicc when it gets cold.
75w-85 advantages:
It's quiet a bit thinner when bitter cold.
Little bit better gas mileage maybe.
That's kinda it.
Disadvantages are:
Ain't got none.
Costs twice as much as mobil1 from what I could find on a lazy internet search.
I think I've only really ever seen it used in front diffs or in euro cars.

Does anyone know any reason not to run 75w-85 gear oil in a rear diff?

 

[edyvw]

You worry too much. I used 75W90 in the transfer case that is filled with 75W. Those are super small differences.

 

[dubber09]

75w-90 and don't look back, just make sure you get LS juice if it's required.

 

[dnewton3]

The difference between 75w-85 and 75w-90 isn't worth the extra effort to use the former over the later.
Put the Mobil 1 in it and be done with it.

 

[D1dad]

I ran motul mineral, 80w90 for the last year in my rogue. Plenty of sub zero take offs and nothing negative to report. I’ll be changing it out to schaeffers 75-90 this week. My front transfer and rear diff hold less than a qt together, so I don’t dare go over 20k. I suppose I could, but I won’t.

 

[BISCUT]

The difference between 75w-85 and 75w-90 isn't worth the extra effort to use the former over the later.
Put the Mobil 1 in it and be done with it.

I'm using 75-90 in multiple applications that call for 80wt and haven't had any issues. One of those applications is a 17 Outback with 200k and a few front/rear diff changes. I don't even look for 85wt anymore. I do like Mobil 1, Valvoline, or Amsoil Severe Gear oil.

 

[oil pan 4]

You worry too much. I used 75W90 in the transfer case that is filled with 75W. Those are super small differences.

From what I can find a 90wt should be about 15 to 16 cSt at 100c.
A 85wt should be around 11cSt at 100c.
Indeed a very small difference.
But synthetic 75w-90 should be like 1,000cSt and 75w-85 should be around 500cSt at 20c. That's the big difference.
There's probably even a bigger difference at -10c, but I can only find a comparison of the 2 oils down to +20c.

 

[oil pan 4]

75w-90 and don't look back, just make sure you get LS juice if it's required.

No LS from what I can tell driving it. I'll know for sure when I get the cover off.

 

[oil pan 4]

I ran motul mineral, 80w90 for the last year in my rogue. Plenty of sub zero take offs and nothing negative to report. I’ll be changing it out to schaeffers 75-90 this week. My front transfer and rear diff hold less than a qt together, so I don’t dare go over 20k. I suppose I could, but I won’t.

With such a small oil capacity that's probably a good idea.

 

[D1dad]

With such a small oil capacity that's probably a good idea.

For sure. I leased the rogue and bought it at the height of Covid. Low interest rates and no inventory made it a no brainer. At 40k I decided I’d go through and change the front and rear as well as the cvt fluid since it was going to be mine. I always did the oil @ 5k or less, (not fair to the next person) not to. And man was the transfer case downright disgusting! Gear fluid in general is bad, but this about made me yak! I’ve done several drain and fills and settled in on once a year for safeties sake. So far motul has been the quietist and I’ve used pennzoil syn and amsoil, schaeffers is on deck.

 

[oil pan 4]

For sure. I leased the rogue and bought it at the height of Covid. Low interest rates and no inventory made it a no brainer. At 40k I decided I’d go through and change the front and rear as well as the cvt fluid since it was going to be mine. I always did the oil @ 5k or less, (not fair to the next person) not to. And man was the transfer case downright disgusting! Gear fluid in general is bad, but this about made me yak! I’ve done several drain and fills and settled in on once a year for safeties sake. So far motul has been the quietist and I’ve used pennzoil syn and amsoil, schaeffers is on deck.

The first oil change in a gear box can be kinda nasty.

 

[D1dad]

I did verify a few years back that the factory fill as well as the overpriced bottles you’d get at a Nissan dealership are pennzoil mineral. The also offer the synthetic version for WAY to much money. Especially considering you can get bot at Menards for a good price.

 

[oil pan 4]

Well the thinner 75w-85 gear oil allowed me to find what is hopefully the last leak on the 9.25 inch rear. For a while.
The speed sensor oring was cut, had a chunk taken out of it. Probably been that way for 26 years.
I jacked it up and ran it at 60mph and the more or less "30wt viscosity" of the 75w-85 oil eagerly ran right down the side of the diff giving away the faulty seal.
This could have been a job accomplished by reclaimed motor oil too.

 

[MaximaGuy]

You are over thinking this small weight difference. 75w90 is readily available and Mobil is top notch stuff. I simply see no reason to put OEM 75w85 when better fluids are readily available. As others have said 75W90 is plenty for most 85 applications

 

[oil pan 4]

You are over thinking this small weight difference. 75w90 is readily available and Mobil is top notch stuff. I simply see no reason to put OEM 75w85 when better fluids are readily available. As others have said 75W90 is plenty for most 85 applications

The difference between 75w-85 and 75w-90 is similar to the difference in a 30wt and 50wt motor oil.

 

[oil pan 4]

I drove a 600 mile trip for the big Juneteenth holiday. Then another 300 today. Seems 75w-85 is sufficient to avoid at least immediate failure.

 

[oil pan 4]

No more leakes.
Ive seen tons of complaints online about dodge diffs from the late 90s and early 2000s leaking.
It's been a week, not seen a single drop hanging off the diff since the day after I replaced the speed sensor seal.

 

[burbguy82]

75w110

 

[oil pan 4]

75w110

I don't think have seen that.
But there seems to be a pretty wide gap between 90wt which is like a 50wt motor oil and 140wt which is like double the viscosity of 90wt at 100c.
That 140wt is some thick S.

 

[burbguy82]

I don't think have seen that.
But there seems to be a pretty wide gap between 90wt which is like a 50wt motor oil and 140wt which is like double the viscosity of 90wt at 100c.
That 140wt is some thick S.

Amsoil and Redline has it.

Amsoil site has an interesting and excellent base for the specs on the 75w110..........which is currently in my daughters Tahoe.........from what I understand, the 90wt of today is on a different scale than in the past........
@Pablo can elaborate on the subject.