Are thicker gear oils better for differentials?

FTTSHO

FTTSHO

Joined
Jan 29, 2022
Messages
202
I’m getting ready to change my differential fluids (front and rear) on my 2001 Chevy Blazer 4door 4x4.

Right now I have Supertech 80w90 Dino gear oil in the front and rear diffs, which I put in about a year ago. There’s no noise from the differentials, so they are in good shape.

I just want to drain the diffs out and put some new fluid in, because last time I drained the diff fluids, the fluid had some metal in it, and it was black, from the previous owner.

Just trying to do some preventative maintenance, just to get the remaining metal out of the diffs!

So would thicker gear oils better protect my differentials?

I’m thinking of switching to synthetic 75w-110 from the recommended 75w90/80w90


Do thicker gear oils provide better diff protection, like thicker engine oils do in engines?
 
Yes thicker oil more film thickness to prevent friction though one would say they don't help if you're not towing and loading it but I still put 140 in my old trucks that still have the original differentials. I imagine they have some wear though I don't know so I'll just use thick oil too help it some. At worst I hurt my mpg by a decimal amount.
 
Simple answer is yes but on an 01 Blazer I doubt you are going to be doing anything with it that requires thicker oil. The 4.3 isn't a super powerful engine and the S10 Blazer was never suppose to tow heavy loads. I'd run some 75w90 synthetic in both and call it a day or if you want to save a few $$$ then just continue to use 80w90 like you have been.
 
It's not as simple as "is this better?" ...

Mainly because you need to define several things for us to understand what "better" means to you, so we can make a good recommendation.
- the application (we've been given a little bit)
- the use (DD; towing; what else?)
- the environment (how hot or cold are your temp extremes?)
- the OCI (how often will you change it? miles?)
- syns or conventional oils?
- is fuel economy a concern? (thicker oils consume energy)

Generally, if you pick something off the PRI QPL you'd have good performance and wear protection.
See the sticky thread at the top of this forum.
 
dnewton3 said:
It's not as simple as "is this better?" ...

Mainly because you need to define several things for us to understand what "better" means to you, so we can make a good recommendation.
- the application (we've been given a little bit)
- the use (DD; towing; what else?)
- the environment (how hot or cold are your temp extremes?)
- the OCI (how often will you change it? miles?)
- syns or conventional oils?
- is fuel economy a concern? (thicker oils consume energy)

Generally, if you pick something off the PRI QPL you'd have good performance and wear protection.
See the sticky thread at the top of this forum.
Click to expand...
-Application is daily driving. Mostly highway.
- No towing. Just occasionally moving around about 500lbs worth of stuff inside the car with 4 people traveling 200-300miles, and driving about 80mph down the highway.
- I live in South Carolina, so it doesn’t ever go below 28F, but it does go above 100F during the summer.
- I plan on changing the diff fluids every 40,000 miles.
- I want to switch to synthetic diff fluids
- Fuel economy is not a concern. I got a Severe duty fan clutch, and the truck gets bad fuel economy already.

I just want the best for my truck. It’s got 108k miles on it right now and I want everything to last as long as possible. I plan on keeping this thing at least for another 200k miles, because I dont want car payments.

Just want to know if 90w is the best choice for longevity.
 
BAJA_05 said:
Not a recommendation on what gear oil brand -- but I can tell you -- the squeeze pack quarts are very easy peasy to use on differentials and transfer cases. I went with Valvoline Synpower 75W90 on my front differential and transfer case most recently with my Tundra.
Click to expand...
Yeah, just put in some Amsoil SG and kept the bags 😉
 
FTTSHO said:
I’m getting ready to change my differential fluids (front and rear) on my 2001 Chevy Blazer 4door 4x4.

Right now I have Supertech 80w90 Dino gear oil in the front and rear diffs, which I put in about a year ago. There’s no noise from the differentials, so they are in good shape.

I just want to drain the diffs out and put some new fluid in, because last time I drained the diff fluids, the fluid had some metal in it, and it was black, from the previous owner.

Just trying to do some preventative maintenance, just to get the remaining metal out of the diffs!

So would thicker gear oils better protect my differentials?

I’m thinking of switching to synthetic 75w-110 from the recommended 75w90/80w90


Do thicker gear oils provide better diff protection, like thicker engine oils do in engines?
Click to expand...
In general yes. The reasonable argument doesn’t need to get really deep when you look at

​

Automotive Lubricant Viscosity Grades: Gear Oils – J 306​


And see that the old SAE 90 gear oil viscosity range was divided in two. New 110 is really just the upper end of the earlier SAE 90 viscosity range
 
I use 75w140 Redline in every differential (6) in 3 trucks and have no issues and very little black goop on the magnets. I'd wager 75w110 isn't going to hurt anything. Might even help the little 10 bolt. I say as a general guide, for a truck or RWD SUV, with that usage I might go a bit thicker but not thinner in my area...your area sounds similar.
Go for 75w110. It might drop the fuel mileage from 16mpg to 15.99995mpg. Nothing in reality for you.
 
On rear axles I worry a bit about flowing to the wheel bearings in cold temps.

For a cute ute I'd stay with a 75W-90 or 80W-90, but in truth it doesn't matter.
 
Consensus is that GM B platform cars generally do better with a conventional 80W90 than a synthetic 75W90, whether it's got the G80 Posi or not. The 80W90s will have higher viscosity under most driving conditions; differential oil spends less of its life at 100+°C than engine oil ever will, possibly never in some cases.
 
I’ll ask this again, since it pertains to the OP’s question.

What temps are considered normal in a standard rear diff? I know towing up a mountain pass in summer will be hotter than short tripping in dead of winter in flatlands, but what are some typical values, for say, 10 miles at 70 mph not towing, in 90F ambient? And at the towing scenario just mentioned? And 2 minutes into a drive starting from cold (say 32F ambient). Some YouTube vid I watched with a clear plastic rear cover showed super cold fluid providing little protection at first as it was flung off the gears and not circulating (whether that’s a real situation or not, I’m not sure, but the point of the video was that most wear occurs in the first few minutes of use, just like with an engine,).

Couple this info with the concept that thicker oil might run hotter AFTER it has fully warmed, sliding its viscosity toward the thinner end of its intended range. So one way to look at this is a 70w might be best for the first 2-3 minutes of any drive, then a little later on, a thicker 75w-90 fluid protects more, but then at extreme end (75w-140) MIGHT not have as clear of an advantage as the 100c viscosity rating might suggest, because maybe it is running at 100c, whereas a 75w-90 might be running at 80c under same conditions…and therefore not as thinned out as the “thicker” fluid. I imagine the 75w-140 might still have a protection edge, but not as great as the lab numbers might suggest.

Again, I mean this as a question, and maybe I’m off on the temp differences between fluids at high load. Maybe if our diffs had cooling systems which regulated the heat, or were heated-garage-kept in winter, the lab numbers (40c, and 100c) might be adequate in determining real-world performance.

Just thinking out loud.
 
Pablo said:
In general yes. The reasonable argument doesn’t need to get really deep when you look at

​

Automotive Lubricant Viscosity Grades: Gear Oils – J 306​


And see that the old SAE 90 gear oil viscosity range was divided in two. New 110 is really just the upper end of the earlier SAE 90 viscosity range
Click to expand...

Well, some here like to give auto engineers wide deference, so here’s the conundrum Ford is presenting me with:

Once upon a time Ford spec’d 75w-140 (or 85w-140) in even their lighter-duty F150’s. At some point, maybe 10 yrs ago, they switched to 75w-85, even in “lighter-duty” 250’s, such as my Transit 250, and I believe even the Transit 350…I don’t know about the super-duty pickups. Somewhere along the line, they must have spec’d 75w-90, as Motorcraft made a full-synthetic in that grade…not sure if still available, and not sure what it was spec’d for. Couple that with @buster post with the spanish-language video complaining the Severe Gear was “hollowed out” from earlier version, and you yourself seemingly pushing more users toward the 75w-110 vs the 75w-90, let alone the new 75w-85 Amsoil now sells. Gets a bit tricky, unless one is a diehard “thickie.”

Do I listen to the Ford engineers (and their dutiful dealers) pitching 75w-85, or you pitching 75w-110 most the time, or strike a happy medium, and just do the SG 75w-90, which performed admirably in @subierubyroo’s shootout, despite being one of the thinner 75w-90’s.

Yes, I’m still kicking tires on this (figuratively, since I broke my ankle, and then my pelvis, can’t actually kick anything, and haven’t put enough miles on either vehicle in the last 6 months to justify any fluid change…barely even gasoline). But the optimist in me is trying to fill my Amsoil cart up so maybe I can change some fluids before it gets too cold in Jan (Texas…may never freeze here again in my lifetime…except for the obligatory 1 week of winter we get each year)
 
Pablo said:
Not sure what you mean by hollowed out. I think you mean J306 specification being changed a ways back, but not sure.
Click to expand...
First off, in my opinion, the SG 75w90 performed in the top two in SubieRubyRoo’s shootout, and I intend to buy some. ( Was just now checking out how to buy thru you). It was the video Buster linked to that said the new formula was not as stout as the older formula (I used the word “hollowed out” but that is what the video said in effect). Much less phosphorous, boron, and something else…also viscosity now less. But I’m pretty sure it was the newer formula the video was b**ching about that did so well in Subie’s shootout.

buster

Thread 'Amsoil Severe Gear 75w-90'

Looks to be a mostly group III, with some PAO and ester.

Comparison to old formulation near the end.

1724409822608.jpg


  • Like
  • Helpful


Now, the one thing still holding me back is whether I should do the 75w90, which is already much thicker than Ford’s spec’d 75w85, or take your recommendation of the 75w110. Heh, I’ve even thought of mixing the 2.
 
You must log in or register to reply here.

Similar threads

S
Noisy differential or CVs? 2012 Sienna AWD
Replies
2
Views
113
D60
Z
Subaru BRZ rear diff with LSD; what fluid?
Replies
8
Views
597
zeroptzero
Z
Rear Differential 75w85 vs 75w90 - Any Benefit Either Way
2
Replies
22
Views
3K
Impatient
tired
Differential fluid recommendation for Toyota and Nissan
2
Replies
20
Views
1K
tired
Strumpan_
Rear diff and front diff/tranny oil for a Audi A4 Quattro?
Replies
13
Views
338
Strumpan_
Back
Top Bottom