Best oils for mpg?

[gotek]

Have an '83 Tercel 4x4 wagon 62 HP engine...that is in FWD most of the time with occasional use of the rear axle.

Currently using a dino 85W90 gear oil with moly in both the front diff/gearbox and the rear diff.

Wanting to try Mobil 1 synth 85W90 in the transaxle (calls for GL-5) and will use either moly or Tufoil additives. Will stay with 85W90 due to higher miles.

Thinking of using Mobil 1 synth ATF in the rear diff using also either a tube of STP diff/gear additive (in a tube...white...zinc?) or some Lubegard ATF additive. Not sure the STP additive will mix with ATF. Not sure a moly gear additive will either.

The idea being to keep viscosity down in order to increase mpg...and use extra additives as high pressure lubes.

Question? Will the ATF work in the rear diff under light loads...what additive would be best to use with it?

 

[addyguy]

Wow. I haven't seen a 4*4 Tercel wagon in years.

They used to be pretty popular up here.....my dad always wanted one, but never got one.

 

[gathermewool]

IMO, drop in 75W-90 M1 and leave out the adds.

 

[unDummy]

Any full synthetic 75w90 is good enough all by itself. There is no need for any additives.

Any gear oil rated GL5 has enough additives all by itself.

I have nothing against Tufoil or Lubegard, but don't see the need for it. If you want a gear oil additive, you could add the Lubegard gear oil supplement(yellow bottle).

Lubegard ATF additives are for ATF. ATF is not a replacement for gear oil.

 

[artificialist]

Synthetic gear oil isn't available in 85w90.

Nearly all Xw90 synthetic gear oils I have seen are 75w90, and only Amsoil has an 80w90.

Synthetic gear oil has all the adds you need, except in certain types of limited slip applications.

One way to reduce lubricant drag is to replace your power steering fluid with synthetic ATF.

Some new cars leave the factory with 75w85 GL5 gear oil in the rear axle to reduce drag. Perhaps that would work, but I wouldn't try it.

 

[Doug Hillary]

Hi,
gotek - Please be aware that diffs that have been on sulphur based gear lubricants for long periods may develop seal seepage when changed to a synthetic! Not always the case - but a distinct possibility

75W-90 synthetic gear lubricants (when used in the correct application) are quite fuel efficient IME. However the efficiency changes within a very similar viscosity spread are only parasitic in reality

 

[mechtech2]

I'd also use the M1 full syn without extra stuff.
Not that all additives are bad, but with the extremely light loading in that vehicle, the M1 is more than sufficient.
You are chasing 1/10 MPG here.
Your right foot will net you 2-5 MPG.

 

[gotek]

Thanks for the responses. Guess I'll go with the Mobil 1 75W-90 all around. Might try the Lubegard gear additive...since I seem to have additives on the brain.

This comes from an experience with a 280ZX that typically got 24 mpg...managed an 8-10% mpg gain from using moly...teflon...militec in the engine every 3K at each change (1 at a time) plus one of the 3 in the gearbox and diff. This was when using standard dino gear oil. Car had no other mods.

Am aware of the placebo effect...where one tends to drive "lighter" when testing some miracle additive. ;-)

In fact I've installed what I call a detent spring on the throttle that adds some slight tension to pedal feel at around the same throttle position as when cruising at 55 mpg in 5th....
works like a vacuum gauge...but nothing to watch.

 

[unDummy]

If your PS requires Dexron, then use a synthetic ATF to flush out the power steering system.

 

[VK56VD]

Use Amsoil or RedLine differential fluid without any additives. Both are synthetic and are the best you can buy for your application and MPG.

Use synthetic ATF for your transmission as well. Amsoil ATF and RedLine are excellent.