What has the biggest Viscosity Index? Gear or eng.

[ueberooo]

What sort of fluid has the biggest Viscosity Index? Gear oils or engine oils, or ATF?

I'm looking a fluid amendment to add to my MT to thicken the fluid at high temperature, without making it too viscous at cold temperatures (near freezing).

In other words, I'd like improve the VI of my MT fluid.

So, I'm currently running ATF 3 in my 1995 subie 5 speed transmission, because the regular 75w140 is too thick in the cold (where the transmission no longer shifts into 2nd gear until the car has reached operating temperature).

With ATF 3 it shifts into all gears; however, there is a slight problem once it's very well warmed up: during shifting from 4th to 5th during higher RPMs. I'll hear that it will grind some part of the transmission (synchromesh?) during this shift. So far, the transmission has put up with a lot of this grinding wear over the years and held up, but if I could improve it, I believe I'd extend the life of the transmission.

So far, my candidates to add into the ATF III are:

STP oil treatment
75w140 gear oil
0W40, eg. mobil
5W50, eg. castrol

How does the 75W140 compare to say an oil like a 0w40 or 5w50, and what else might you consider as an additive candidate? If it matters, the transmission is integrated (shares fluid) with the AWD differential--and I believe I've heard that stuff too rich in slippery stuff like MoS2 is not recommended).

 

[Quattro Pete]

Have you looked at this?

http://www.bobistheoilguy.com/index.php?option=com_content&view=article&id=48&Itemid=55

 

[SuperDave456]

How cold does it get up there?

Edited to add: What does the manufacture reccommend? I just realized that this is an Automatic and not a manual transmission. Perhaps look up that reccommendation on the Amsoil or Redline website. Full Synthetics do a better job at either tempature extremes.

I have the opposite problem down here in Tx. I worry about burning of fluids while under load during the summer. My father-in-law recently gave me his Ford F-150 and I replaced all the fluids in it.

If it was me I would think about something like Amsoil's 75w140. I have it in my rear differential and although kind of expensive, it should last a few years.

From their website:
AMSOIL SEVERE GEAR® Synthetic Extreme Pressure (EP) Lubricant SAE 75W-140 (SVO)
Kinematic Viscosity @ 100°C, cSt (ASTM D-445) 25.7
Kinematic Viscosity @ 40°C, cst (ASTM D-445) 184.3
Viscosity Index (ASTM D-2270) 174
Brookfield Viscosity, cP (150,000 Max) @-40°C 128,200
Flash Point, °C (°F) (ASTM D-92) 150°C Min. 212 (414)
Pour Point, °C (°F) (ASTM D-97) -48 (-54)
Copper Corrosion (ASTM D-130) 1b Max @ 121 °C (250°F) / 3hr 1b
Falex Procedure B (ASTM D-3233) (failure load, lbf.) 2500
Foam Stability (ASTM D-892) (20/50/20 maximum) 0/0/0

 

[MolaKule]

If you have to use ATF in your Subies MT, I would look at a drain and refill using Redline Racing ATF or the High Temp ATF.

Both have viscosity indices above 170 and viscosities of 10 cSt.

 

[ARCOgraphite]

Why dont you run a 75w-85/90? GL4 safe? The heavier stuff is highly additised HD truck hypoid and will casue synchromesh problems. Many folks with subies like the plain old semisyn Warren supertech GL-4/5 safe for synchrohubs.

 

[edhackett]

Subaru manual transmissions require a GL-5 fluid. They have a hypoid differential. 80w90 would have been called for in 1995. 75W-90 will work fine, and is the current requirement.

You are using ATF and 75W-140, neither of which is approproate for your transmission and want to use a bunch of other oils that have no business in a Subaru transmission. Why don't you you use what the transmission/differential was designed to use. Unbelievable.

Ed

 

[PT1]

Originally Posted By: MolaKule
If you have to use ATF in your Subies MT, I would look at a drain and refill using Redline Racing ATF or the High Temp ATF.

Both have viscosity indices above 170 and viscosities of 10 cSt.


How about redline MTL?

 

[edhackett]

Redline 75W-90NS is the proper choice. People have good luck with the Valvoline 75W-90 non synthetic, Chevron Delo ESI 80W-90, and of course the Subaru Extra S 75W-90.

Ed

 

[MolaKule]

If this Subie does indeed have a transaxle with a hypoid differential enclosed and requires a 75W90, then you would need at least something like Redline MT-90 or Amsoil MTG. The EP package has almost the same concentration as do differential lubes and should shift better.

None of the candidates you mentioned in your first post are acceptable.

 

[unDummy]

Ueberooo, we need more specifics.
What does it require? AWD/FWD? What model/engine?
What is ATF 3?

 

[ueberooo]

Originally Posted By: edhackett
Subaru manual transmissions require a GL-5 fluid. They have a hypoid differential. 80w90 would have been called for in 1995. 75W-90 will work fine, and is the current requirement.

I initially tried Valvoline 80w90, it would shift poorly, and in the winter wouldn't make it into 2nd gear. I checked out the subaru forums trying to find other people with similar problems (an aging no longer properly functioning MT) and found one post about a guy using Automatic transmission fluid to solve the shifts; admittedly is will increase wear, but still seems to be the lesser of two evils). When I wear out my MT, or my clutch, I plan to get the whole transmission replaced with a properly functioning one; it's somewhat inevitable, I'm just trying to get as best a milage as I can out of my transmission; so far almost going on 5 years with this problematic transmission.
Originally Posted By: unDummy

Ueberooo, we need more specifics.
What does it require? AWD/FWD? What model/engine?
What is ATF 3?

Ed is right, it's an AWD 5 speed; the manual says it requires 80w90, but I tried it years ago and it had the problems I described since my MT seems somewhat defective. I can maybe give Molakule's suggestion and try Redline MT-90 or Amsoil MTG after the winter ends.

Typical winter temperatures in Portland are just 40s, but it can get as low 20 F or even lower on record days.

 

[ueberooo]

Originally Posted By: ARCOgraphite
GL4 safe? The heavier stuff is highly additised HD truck hypoid and will casue synchromesh problems.


Hi Arco, why does that happen? Is there an easy quick explanation of why roughy the 75w140 additised stuff wreaks havoc on the synchromesh? I'm actually a little worried about mine (because shifting from 4 to 5 it does often make noises).

 

[unDummy]

If a mineral 80w90 is giving you problems, then any full synthetic 75w90 will be an improvement.

Motul Gear300, Torco RTF, Redline 75w90NS, Ford's XT-75W90-QGT, Silkolene Silktran, Synlube MT, Eneos MT, RoyalPurple Maxgear, Torco RTF, Neo 75w90HD, ...... are all GL5 90wt gear oils for usage in manual trannies and/or non-LSD gearboxes.

GL4 is definitely better than ATF since you are risking excessive wear with ATF. Redline MT90, Idemitsu MTF, or Amsoil MTG are great gear oils.

There are 75w85 GL5 gear oils that should work well too since you're in a colder climate. But, hard to find locally. Toyota dealers stock 75w85 non-LSD gear oil.

 

[aquariuscsm]

There`s always Redline Heavy Shockproof. Isn`t it supposed to be a 75W250?

 

[mechtech2]

Like the guys said, don't mess with lame additives to ATF.
Get a real gear oil.
Redline or Amsoil have great products.
You don't have to buy the thickest one.