Significant MPG increase after Diff fluid change??

[Rex]

Yesterday I replaced my front and rear differential fluid in my 2011 Subaru Outback. I went with a quality full synthetic Schaeffer Supreme gear lube 75w 90. My MPG went from 28ish to 33-34 MPG. Is this normal?

 

[gathermewool]

No, 100% not possible. Were the differentials nearly empty?

 

[Eddie]

You got to be joking if you measured ANY increase in mileage.

 

[Rex]

No.. I just purchased the car 3 weeks ago with 91K miles and was its first diff fluid change. For the past 3 weeks the computers MPG displayed 26-28 MPG consistently. Now its in the 30 plus range. I put back what I pulled out for the fluid amounts..


Originally Posted By: gathermewool
No, 100% not possible. Were the differentials nearly empty?

 

[CT8]

Schaeffer Supreme gear lube Is wonderful gear lube.

 

[HTSS_TR]

If the old fluid was 75W140 then you may gain 0.2 to 0.5 MPG, but that amount is just noise, a slight different in speed and wind condition effect MPG much more than that.

 

[buck91]

Probably just coincidental timing to the gear change and was caused by new owner and new driving habits. Or maybe weather changes?

 

[Nate1979]

Not possible.

 

[901Memphis]

Maybe if it had oxidized and thickening heavily, sae 140 gear oil is as thick as it gets

 

[gathermewool]

Originally Posted By: Rex
No.. I just purchased the car 3 weeks ago with 91K miles and was its first diff fluid change. For the past 3 weeks the computers MPG displayed 26-28 MPG consistently. Now its in the 30 plus range. I put back what I pulled out for the fluid amounts..


Originally Posted By: gathermewool
No, 100% not possible. Were the differentials nearly empty?


IME, the Subaru MPG readout is optimistic, but usually pretty consistent. With that said, how many miles are you talking about for the change to have taken place? Unless it's over AT LEAST a few gas tanks, it's worthless. I used to get 34 MPG in my STI on the way home from the gas station, because the car was already warmed up and there were a lot of spots where I could coast and engine-brake down hills.

To be accurate, you need to actually calculate your MPG, not just rely on the computer display.

 

[toneydoc]

That must be some good stuff. Gonna go get some and change mine this weekend.

 

[HangFire]

Computer readouts are all over the place. I trust only mileage versus my fillup amounts.

 

[Garak]

Originally Posted By: Rex
My MPG went from 28ish to 33-34 MPG. Is this normal?

A 21% improvement in fuel economy from simply changing differential fluid isn't feasible, unless there was virtually solid tar in there before.

 

[Joel_MD]

What the computer shows is not your actual fuel economy. If you want to keep tabs on your actual fuel economy, one way is to reset your trip odometer when you fuel up and the next time you fuel up just divide the miles by the amount of fuel needed to fill the tank. Another way is to use an online tool like Fuelly.

 

[stchman]

If the differentials were empty I could believe it.

 

[Rex]

Thanks for the suggestions. Like I said, I've only owned the car for 3 weeks and its the first time seeing the MPG go up over the 30+ MPG, and this just after the diff. fluid change. It must have been a fluke because now its back down to normal (28 MPG) so I should have driven the car a bit longer.

 

[Garak]

It happens. Something weird with the weather (i.e. a giant tailwind), a change in your driving habits and/or traffic, all kinds of seemingly small variable can play a significant role.

 

[Nick1994]

I wish that were possible. I'd be out changing my differential fluid too right now.

I've been putting it off for weeks