M35 calls for 80w-90. Use 75w-90 synthetic?

[NormanBuntz]

My wife's 2007 M35 has 99K miles. Rear diff has never been serviced. Owners manual calls for GL-5 80w-90 conventional gear oil. I bought Castrol Syntrax 75w-90 synthetic for a DIY change. It is a GL-5.

Castrol customer service won't recommend it because it differs from the OM. Should I use the Syntrax? What real difference would the 75w grade make?

 

[khittner]

I don't have an Infinity, and I haven't used Syntrax, but Castrol makes fine products and it'll probably be fine. I've used Mobil 1 75W-90 synthetic gear oil in the spec'ed-for- 80W-90 manual trans and differential of my Dodge truck (like I said, it's not an Infinity) since shortly after it rolled off the truck at the dealership---somewhat better cold weather (like northeren Wisconsin -20F ambient cold weather) shifting at/near start-up; no warm weather issues at all. Truck has 216K miles on it, and the trans and differential have not needed service beyond oil changes. Pour in your synthetic 75w-90 and drive on.

 

[zeng]

80W90 has higher KV@40*C and more shear stable, hence offers stronger oil film thickness and stronger protection....
than a 75W90 of lower KV@40*C and more prone to viscosity shearing in use.

 

[TexasVaquero]

My versa's transmission uses 75w85. I decided to buy the Nissan gear oil. Desu

 

[901Memphis]

The 75w90 would perform better in freezing conditions and is superior to the mineral 80w90, I would use it without hesitation if the rest of the specs match up.

 

[Garak]

I did basically what you're doing, just with another brand.

 

[Sayjac]

Short answer, I'd say absolutely use it!

Longer answer, the good folks at Castrol CS are in CYA mode here, ie., not going to recommend or endorse anything outside the OM recs of 80w90. However you understand that Syntrax 'synthetic' like M1 'synthetic' and Valvoline synthetic covers 75w90 viscosity, better flow at lower temps. And you're not under vehicle warranty either so that's not a consideration.

As an aside, just bought 3qts Syntrax from AZ for an 01 Tacoma that also specs 80w90 (no mention of 75w90 either), and did differential d&f. No worries here at all. Meets GL 5 and limited slip.

One tip, make sure you find/keep the drain bolt crush washer when you pull it. It might fall off into the drain pan in the process without one being aware it.

 

[barkingspider]

I have used 75w90 in 80w90 applications and vice versa. Zero issues. You are good to go

 

[mightymousetech]

Absolutely no issues at all doing that.

 

[umungus1122]

The diff uses a 90 weight. A synthetic GL5 75w-90 is superior to a conventional or blend 80w-90.

 

[aquariuscsm]

Originally Posted By: NormanBuntz
Owners manual calls for GL-5 80w-90 conventional gear oil.


Use either Amsoil AGL 80W90 or Amsoil Severe Gear 75W110.

 

[xtell]

Use it without concern. Better low / high temperature protection.

 

[Trav]

Running Amsoil severe gear 75w90 in an 06 M35X for the last 6 or so yrs with no issues whatsoever.

 

[Hootbro]

Unless intended use is expected in an extreme cold environment like below zero temps, 75W-90 and 80W-90 are interchangeable for the most part.