Lucas oil and MPG

I changed my 2017 MT Taco gear oil after the 500 mile break in period with some Lucas 85w-140 and now my MPG dropped around 15%.

Is this normal? I expected a few percent decrease with the high viscosity gear oil...but 15%? Damn...not cool.

Also differential is hot hot hot, normal?

 

Higher viscosity = higher temperatures due to friction losses, also why your mpg dropped.

 

Do you tow a lot? What's the reason for the 85w-140?
Sorry, no input on real world mpg loss/heat generation...

 

No Towing at this time. Only street and HWY miles.
The Nitro Gear calls for 80-140 or 85-140.
Gear shop recommended it, ECGS as well and countless others online.
I couldn't find anyone complaining about the reduction of MPG, thus I was bit shocked of my situation. I started second guessing my work and rechecked the oil, etc.

Its not my daily, I shouldn't complain. I am only curious if others came across the same issues.

 

Did you get gears upgraded? Such as 4.88 or higher?

Lift? Bigger tires? If so, that's the reason.. Most people get around 15 MPG.

Mostly stock will get 18 to 24 MPG depends on conditions.

 

Im going to guess they got new gears, no way are they doing a 500 mile break in change on a 2017 when its 2022 now.

 

It's not the lubricant. It's the other changes that were made.

Have you corrected your calculations due to speedo error?

 

5.29 gears yes, I have 315's, steel bumpers, mid travel lift..

I have not corrected any calculations, I am purely going on the digital display. Prior to the diff. oil change, post 5.29 gears, the display claimed I was getting 17.3 average. I changed the front and rear diff oil with this Lucas stuff like instructed and immediately my mpg felt the impact from the high viscosity oil.

I'm a little shocked about the reduction of 15% mph from this oil. I suppose the idea is the gears n pinion spin at a greater rate and thus more friction/heat thus higher viscosity oil is required. FML!

Imp curious if others have felt similar losses post break in period with this oil?

 

after running 85W-140 for two changes when my 4.88’s were new, I noticed some slight mpg decrease on highway trips.

I have since gone with Amsoil 75w-110 and it has been solid for towing or not towing ever since

 

What's required is what Toyota put in there.

 

He's got aftermarket gears, they call for higher viscosity.

 

Nitro wants you to use that fluid because it reduced the volume level of their gears whining. They give all kinds of goofball justifications about 85/140 being “more oily” and “heat remaining in the gears, not in the oil, when synthetic is used”, but generally they are just covering for the fact that cheap aftermarket cut gears will never be a quiet as Toyotas forged OEM gears.

So you can run 85/140 and have reasonably quiet gears, but lesser MPG, or run 75/90, burn less gas and listen to those Nitros whine.

FWIW I have Nitro 4.88s and run 85/140 to reduce whine.

 

Sheeet, gears whining is the least of my concerns.
As long as it can protect my gears and diff with lower Viscosity , I’m totally cool with a lil noice… shit the more the merrier

 

For whatever it's worth, I have been rolling with

$28 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90 in my nitro 4.88s for almost 18 months without problem. I actually drained and filled the rear diff today with the same, after about 22000 miles. There was a minute amount of shavings on the magnetic plug. This was the first change post 500 mile break-in. I wasn't worried about what I saw. I'm open to feedback if more experienced folks have something to add.

Edit to mention I have never experienced a whine

 

It’s a pretty noticeable difference. The whine on my truck is pronounced with 75/90, but manageable with 85/140. I tried 75/110 but it was the same volume as 75/90. 85/140 does shut ‘em up.

 

okay, fair enough.
Thanks guys.