gear oil for better mpg's

[gtx510]

I'm going to change the tranny and diff fliud in my g/f's Frontier.

I don't want to use MTL because I heard it causes wear in Nissan trannies (4-cyl truck tranny is the same as the 240SX).
And it seems to thin for socal weather (bearing noisse in my other trannies).

My choices are MT-90 and RP's Synchromax.
RP is thinner but does it protect as well as MT-90?
I'm leaning more towards MT-90 cuz I don't think they have Synchromax at Napa, just Maxgear.
I can get Redline locally...

Is Super Lightweight Shockproof thinner than MT-90?
Shift as well?
Could I also use it for the diff? No towing...

Or Mobil1 75W90 for the diff? Seems like the thinnest one out there?
Thinner than Lightweight Shockproof?

 

[cryptokid]

i am running mt90 in my transmission, and i am getting 1-2mpg better then when i used valvoline synpower 80w90. i know 1-2mpg is within statictical "white noise" but i am constantly getting this result more often than when i get 1-2mpg worse than synpower. so i would have to say yeah, mt90 does give an increase in fuel economy, atleast compared to synpower anyways. at approximitly 1mpg better you would have to go through a couple hundred gallons of gas before the mt90 payed for its self. a couple hundred gallons of gas is not hard to burn through on most cars over the course of a couple months time.

on my car, driving 15,000 miles a year at 35mpg consumed about 500 gallons of gas, so mt90 payed for its self in under 6 months, for me and my car anyways.

 

[gtx510]

I know cost analyze wise I'm gonna save $$.
I want to know what's the thinnest stuff I can get away with in a hot climate.

Does RP Synchromax protect as well as MT-90?
Or how about superlight shockproof? It's thinner than both the ones above?

And could I use superlight SP in the rear axle or is that too thin?

 

[Michael SR]

redline doesn't recommend the use of shockproof on the street. more than that, if you read their blurbs really carefully, you'll see that the different weights are very specifically aimed towards certain types of racecars. the light is meant for small formula type cars, like formula v. the superlight is touted as being for qualifying only, hardly a testament.

a long time ago i think the shockproof was different in its additives. their literature used to say it was good for use in gearboxes. now dave at redline told me it's not made for use with synchonizers in most modern cars.

RP- i had a bad experience with that stuff. i've used synchromesh in my car before, and it seems to work fine. when i put in synchromax, it initially worked fine, then became increasingly notchy. it deteriorated to where i sometimes had difficulty putting it into 1st gear. when i drained it, after only a few thousand miles, the little cup in the drain plug held about 4 times the amount of little brass shavings it usually does.

all could be a coincidence, or maybe a bad batch, i don't know. but i've not had problems with the tranny since then, using other lubes. plus, synchromax is like MTL in viscosity, so probably not a good choice for your car.

-michael

 

[SteveD2]

i ran amsoil 75w90 in 2 diffs (one a clutched LSD), a transfer case, and a 5spd in my '89 pathfinder. started at 30k, ended at 190k, changed once (though it looked like new after 100k). no friction additives for the LSD, straight 75w.

*never* had any work done on any of the gearboxes (ever!), and raised average fuel economy 2-3 mpg consistently. highly recommended.

dookie

 

[Bror Jace]

gtx510, you're asking a lot of good questions ... but they are application specific and unfortunately I don't think anyone here is going to be able to answer them to your satisfaction.

I will say that going with a too-thin gear oil may produce accelerated wear and you'll only get the symptoms after wear has started (rear-end howl). So, unless you want to sample your gear oil often (10,000 miles or so) and have it tested (pricey and a pain!) I wouldn't experiment with an oil with is thinner than recommended in your manual.

When in doubt, use a viscosity the same as spec'd in your manual and don't worry too much about the tiny amount of additional fuel.

There are other things you can do to obtain a smidgeon more fuel economy which aren't as risky: maximum tire inflation, avoid idling, etc ...

--- Bror Jace

 

[gtx510]

I've noticed the RL literature flip-flops on whether on not you can use shockproof in a tranny.
This no shockproof for the street is new to me.
The Mazda GTX/GTR guys think it's the best stuff for our transaxle, t/c, diff...

What makes shockproof non-streetable?

fwiw, Redline does say that superlight SP has the viscosity of a 75W90.
Sounds like it should be think enough for a diff?

I think i'm going to run MT-90 in the tranny (maybe with 1qt lt-wt SP) and a mix of Mobil1 75W90 and lt-wt SP in the rear axle.

Might try Redline 75W90NS in the tranny of my GTX.

 

[sprintman]

Isn't Amsoil S2000 gear oil meant to be tops re fuel economy?