Diff fluid mpg results (1 Viewer)

[LWC]

I’ve been breaking in my lockers over the last week and have some interesting observations on differential fluid and mpg.

OEM (pre locker and gears) 14mpg
Amsoil 75-90 svg: 16mpg
Redline heavy shockproof: 14 mpg
Amsoil 75-90 svg front, 75-140 svg rear: 15.5 mpg

 

[LWC]

I’ve been breaking in my lockers over the last week and have some interesting observations on differential fluid and mpg.

OEM (pre locker and gears) 14mpg
Amsoil 75-90 svg: 16mpg
Redline heavy shockproof: 14 mpg
Amsoil 75-90 svg front, 75-140 svg rear: 15.5 mpg

One additional interesting data point is that I have the faintest hint of whine, but I can really only tell if the radio is off and I’m listening for it actively. I played around with these different fluids to see if it would have any effect however, they all sound basically the same.

Given the mpg results, I’ll probably pull out the 75-140 from the rear and replace it with 75-90 the next time I change it.

Last, but not least, I shaved a full half second off my 0 to 40 and 0-60, lmao .

 

[JDUB fab]

Love the information, can we get some other numbers: wheel size and other modifications for comparison.

 

[LWC]

Love the information, can we get some other numbers: wheel size and other modifications for comparison.

Love the information, can we get some other numbers: wheel size and other modifications for comparison.

Stock wheels right now :O! I think I might be the first person to regear a gx on 30” 265/60/18s, but it def. Made city driving nicer and you can’t really feel a difference between 2000 rpm @ 80 mph and 2300 rpm @80 mph. The real thing I wanted was lockers, and I figured if I was in there and planning on putting bigger tires on down the road I might as well do the gears at the same time.

Later in the year when I put bigger tires on, debating between 285/70 and 285/75, I suspect I won’t be able to hear any of the whine that I can pick up on right now if I’m focused on it.

 

[JDUB fab]

Stock wheels right now :O! I think I might be the first person to regear a gx on 30” 265/60/18s, but it def. Made city driving nicer and you can’t really feel a difference between 2000 rpm @ 80 mph and 2300 rpm @80 mph. The real thing I wanted was lockers, and I figured if I was in there and planning on putting bigger tires on down the road I might as well do the gears at the same time.

Later in the year when I put bigger tires on, debating between 285/70 and 285/75, I suspect I won’t be able to hear any of the whine that I can pick up on right now if I’m focused on it.

Nothing wrong with some foresight. What gear ratio did you go with? And lockers?

 

[Roody]

Just looking at the manual for reference, OEM diff oil is 75W-85 GL-5 or equivalent, 1.48 qts for the front and 2.85 qts for the rear.

As far as I can tell the maintenance schedule says to first inspect the diff fluids at 60k miles / 72 months. Of course it recommends replacing the fluid if you're "towing, using a car-top carrier, or heavy vehicle loading." Doesn't seem like there is any point at which they outright recommend replacing it.

@LWC What kind of weather and conditions do you drive in? Warm/cold, stop/go or highway? A few years back I replaced the diff fluid in my 4.7 4Runner and lost MPG, though it was a ~270k mile truck so I put in a heavier duty fluid that was supposed to help preserve worn components. Interesting that your MPG improved with a thicker, higher-viscocity fluid.

 

[LWC]

Just looking at the manual for reference, OEM diff oil is 75W-85 GL-5 or equivalent, 1.48 qts for the front and 2.85 qts for the rear.

As far as I can tell the maintenance schedule says to first inspect the diff fluids at 60k miles / 72 months. Of course it recommends replacing the fluid if you're "towing, using a car-top carrier, or heavy vehicle loading." Doesn't seem like there is any point at which they outright recommend replacing it.

@LWC What kind of weather and conditions do you drive in? Warm/cold, stop/go or highway? A few years back I replaced the diff fluid in my 4.7 4Runner and lost MPG, though it was a ~270k mile truck so I put in a heavier duty fluid that was supposed to help preserve worn components. Interesting that your MPG improved with a thicker, higher-viscocity fluid.

Conditions are very mild, located in SoCal. But mostly a mix of city/highway.

The gears are 456. I don’t have any data with fluids on stock gears since the reason I swapped fluid was because I was regearing.

I think the mpg difference is caused by the gears, I would suspect that on stock gears that oem and amsoil 75-90 would deliver comparable mileage. On the other hand, I think the heavier oils will have a measurable impact but that’s an inference based on what I posted above.

 

[r2m]

As expected, lower gears will give you a better stoplight-to-stoplight times. I remember my 'ol best friend in high school who had a '69 Firebird 400 (with the tachometer on the hood!) which he was building out and all he was concerned about was short runs so he regeard. Man! Was that fast!! But at 70 mph his engine was at about 5000 rpm. His top end sucked (not to mention mpg)... But don't mess with him at street lights!

I have a buddy who's a retailer for Amsoil and he swears that replacing all your fluids (including diff's) with Amsoil will increase mpg. I've never done it but there's a lot of chatter on the internet that claims Amsoil does increase mpg.

 

[Rednexus]

Come to think of it, I've noticed a slight reduction in MPG since using Valvoline 80W90 conventional in my diffs instead of Lucas 75W90 synthetic. I've started running Mobil 1 Delvac synthetic 75W90 in my TC as it's one of the only synthetic gear oils that does not contain a limited slip additive, and I was getting gear noise with the Valvoline. It's also only $9/QT, is used all of the time in the HD truck world, and has very good reviews. My TC is running quieter than with Valvoline 80W90.

Regarding replacement intervals, if you are doing any amount of water crossings, replace it yearly. It does not matter if you have an extended diff breather or not. When the hot differential hits cold water it will suck it in past the seals. My fluid is disgusting after 12 months and 12K miles, with a tiny bit of water in it. The back is always worse than the front, and the transfer case is always totally fine (going to replace it to every 2 years on that). Probably not an issue for folks in the desert, but definitely an issue for those of us in wetter climates.

 

[LWC]

I’ve been breaking in my lockers over the last week and have some interesting observations on differential fluid and mpg.

OEM (pre locker and gears) 14mpg
Amsoil 75-90 svg: 16mpg
Redline heavy shockproof: 14 mpg
Amsoil 75-90 svg front, 75-140 svg rear: 15.5 mpg

Schaffer 75-90 front, 75-140 rear (both conventional ) 14.2 mpg. On 3.91 oem gears.


Update following my return to 3:91s.

 

[jeremy j]

Why did you go back to stock gears?

 

[LWC]

Why did you go back to stock gears?

I couldn't tolerate the whine from the 456s.

 

[jeremy j]

I couldn't tolerate the whine from the 456s.

Makes sense. I am planning on being very careful to not lose the quiet and "lexus" part of my GX as I make changes. It is part of what makes the truck feel so special.

 

[OCGX]

I had a hard time finding what oil is recommended for my Nitro Gears. ECGS recommended 85w140 which is what I have been running.
Would going to 85W help with your gear noise?

 

[LWC]

I had a hard time finding what oil is recommended for my Nitro Gears. ECGS recommended 85w140 which is what I have been running.
Would going to 85W help with your gear noise?

I experimented with AMSOIL 75-90, 85-140, redline heavy shock proof and nothing made a difference.

So I didn't design the gears, but I would think, from a mechanical engineering perspective, that the bearings and their clearances are what actually drive gear oil viscosity. You want the bearings to roll, not slide and then basically float on a thin film of oil. That would push me closer to stock oils, but then again, so many people run 75-140 or even heavier oil without issue, that I really don't think it matters much.

With that said, I believe the hypoid gears themselves drive the addition of high pressure additives to the oil since they have some degree of sliding contact as they mesh.

 

[r2m]

I experimented with AMSOIL 75-90, 85-140, redline heavy shock proof and nothing made a difference.

So I didn't design the gears, but I would think, from a mechanical engineering perspective, that the bearings and their clearances are what actually drive gear oil viscosity. You want the bearings to roll, not slide and then basically float on a thin film of oil. That would push me closer to stock oils, but then again, so many people run 75-140 or even heavier oil without issue, that I really don't think it matters much.

With that said, I believe the hypoid gears themselves drive the addition of high pressure additives to the oil since they have some degree of sliding contact as they mesh.

Just a reminder that although some run heavier oils, viscosity thins with heat. So what may be bearing sliding when one pulls out the driveway, everything should be rolling nicely on the highway, even the higher viscosity fluids. Just that the thicker fluids will still provide enough coating for that "rolling" experience when the diff's get hot from heavier loads like pulling trailers or low range steep crawling.

 

[LWC]

Schaffer 75-90 front, 75-140 rear (both conventional ) 14.2 mpg. On 3.91 oem gears.


Update following my return to 3:91s.

Update to the update:

15.5mpg on amsoil 75-90 with 3.91 oem gears and front/rear e lockers.

I think it's rational to use the unicorn blood..... if I change it every 30k miles, it's worth about $560 in gas savings. More importantly, that extra 20 miles per tank is quality of life improvement, lol

 

[Bleu62]

Ordered. Anyone relocate the breather? Is it worth it? I do occasionally get into high water living in a coastal/tidal area. Sometimes up to 2’ possibly more but man I hope not.

 

[LWC]

Ordered. Anyone relocate the breather? Is it worth it? I do occasionally get into high water living in a coastal/tidal area. Sometimes up to 2’ possibly more but man I hope not.

I did. I Ran it and my e locker cable right along side the break lines. Figure if the brake lines are long enough not to bind, then neither will the breather or cable. Also looks cleaner than running them straight up from the center of the axle.

 

[r2m]

Ordered. Anyone relocate the breather? Is it worth it? I do occasionally get into high water living in a coastal/tidal area. Sometimes up to 2’ possibly more but man I hope not.

It kind of depends upon where in the country you live. Here in So. Cal. The shop that did the work for me and ALL they do is hardcore Toyota's and Lexus, I asked them and the owner said it's really not worth it where we live.
But again, that my location. You don't have a location on with your name, so not sure what to say for your situation...