Should I go thin in the diff?

[Nayov]

I have a 2005 Nismo Frontier 2 WD with 24,000 miles. It specifies synthetic 75W-140 (M226 axle); other models, use the M220 axle but call for 75W-90. The truck lives a charmed life in that it only hauls air in the bed, never tows and being a 'winter wagon' it never sees hot temps (not used in the summer).

The axle has a electronic locking differential which I never use.

I want to go thin and use 75W-90, synthetic of course, for an incremental improvement in MPG and for a possible, but highly unlikely, a bit of a performance boost.

Sound like a plan? I find it hard to believe that a -140 is necessary given the gentle conditions under which it operates, but of course "don't stray from the manual" is a common theme here.

Do any powered performance cars or full sized trucks use 75W-90?

 

[JHZR2]

I'd seriously consider running a 75w-110 like synthetic Amsoil SVG. I likely wouldnt go to a 75w-90 if they are speccing a 140.

 

[dave1251]

Originally Posted By: Nayov
I have a 2005 Nismo Frontier 2 WD with 24,000 miles. It specifies synthetic 75W-140 (M226 axle); other models, use the M220 axle but call for 75W-90. The truck lives a charmed life in that it only hauls air in the bed, never tows and being a 'winter wagon' it never sees hot temps (not used in the summer).

The axle has a electronic locking differential which I never use.

I want to go thin and use 75W-90, synthetic of course, for an incremental improvement in MPG and for a possible, but highly unlikely, a bit of a performance boost.

Sound like a plan? I find it hard to believe that a -140 is necessary given the gentle conditions under which it operates, but of course "don't stray from the manual" is a common theme here.

Do any powered performance cars or full sized trucks use 75W-90?



GM trucks use 75W-90.

 

[gathermewool]

With so few miles/year, I wouldn't worry about the small, if any, increase in mileage you're hoping for. With that being said, and taking your use into consideration, I'd personally be comfortable using something like Amsoil's Severe Gear or Redline's Lightweight Shockproof 75W-90 over an OTC synthetic 75W-140, like Mobil.

 

[Nayov]

Oh I like the idea of -110 a lot. I am boycotting Amsoil though.
Great suggestion.

 

[skyship]

Never, ever put a non approved oil or fluid in any part of the transmission system, even for a top up. If in doubt read the manual or ask the senior engineer at the dealer. Most modern boxes or diffs already use a thinish oil for fuel economy reasons, so going lighter will result in a big increase in wear factors and void any warranty.
Using a synthetic or conventional makes very little difference in wear terms, so if the manufacturer approves both types, just pick the cheapest. The axle you list almost certainly has different bearings to previous models (Probably cheaper ones), so it requires a different oil.

 

[hisilver]

He is likely out of warranty. There has to be a reason for the 140 recommendation. A lot of bearings and gears and maybe clutches in the rear....if it were me I'd stick with 75/140 especially since its used infrequently.

 

[mechtech2]

In your case, you probably can go lighter with no problems at all.
I wouldn't expect any measurable benefits, though.
So change it to flush or renew it, not for any hope of gains.
It's your call, and the Amsoil 110 sounds like the best option.

BTW, umpteen jillion people have used gear and tranny lubes not spec'd for the vehicle, with improved wear, shifting, noise, etc..
Ignore skyshi_.

 

[Doug Hillary]

Hi,
Nayov - To answer your query, yes, many full sized Trucks use 75w-90 synthtic. In my Eaton (DS461P) tandem drive axles I changed from 85w-140 to 75w-90 synthetic with great results. This was on lifetime (1m + kms) OCI - after about 1kkms on FF

Temperature reduction was about 20C and seal/bearing changeouts became a thing of the past!

Use the Manufacturer's recommended lubricant but seek advice from a respected dealer if going down in viscosity. Otherwise take a number of before and after temperature reading over time

 

[buck91]

I upspecs from motorcraft 75w-140 to M1 75w-90 in my 1996 Mustang GT with the 8.8 trac-lok rear. Worked great- until the next owner blew a seal and wheel bearing. Its been a while but I beleive the same thing happened to a Crown Vic with the 8.8 for me as well.