Subaru's lightweight 75W80 gear oil

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Apparently, Subaru has recommended a special, lightweight 75W80 gear oil for manual transmissions that have "beat the syncro" shifting problems. The part number is K0323F0091.

My basic understanding of gear oils is that putting a 75W80 in place of the usual 75W90 or 80W90 may provide better syncro action and faster shifting, but at the expense of gear protection under heavy loads or shocks.

Can you experts weigh-in with opinions on this? Seems odd that Subaru would recommend a lighter oil for their heavily stressed manual transmissions.
 
I agree with you. It's tough to have it both ways - faster shifting and good lubrication for the gears.

I guess it's Subaru's way of making the transmission all wear down at the same time. No sense in keeping the gear teeth well lubricated if the transmission needs to be torn down anyhow for new synchros.
 
That's what I was thinking.

I used to have an aftermarket turbocharged 2.5RS with the fragile 5-speed. I lived in daily fear of shearing the teeth off 1st or 2nd.

Now with the "indestructible" STI gearbox, which gets syncro problems but has little chance of breaking teeth, a lighter gear oil might be OK.
 
Jon, I replied to your post on NASIOC. I don't think the 75w-80 is the right oil. There is another "Gear Oil Extra 75w-90 GL-5" which is the correct one. I wouldn't deviate from the manual's recommendation of a 90w.

I would recommend Mola's SF MTL-R. It has been great to me so far, great to a few other Subaru owners, and great to many other owners here.

I'm not sure whether it is a miracle oil and whether it can fix the Subaru people who already has grinding synchros. But to me it's the best oil by far which satisfies factory spec.
 
Hi,
I installed Castrol Syntrax 75w-90 GL5 synthetic oil throughout (transaxle/rear diff) my MY02 Outback 2.5 Manual when new and at around 200kms
The oil was not changed or topped up again

I recently sold this wonderful car with 130k kms on it. The gearshift quality was still "as new" (excellent) and the red Syntrax was still clean (blotter tested) and clear

Regards
Doug
 
Syntrax is a Castrol GL-5 75w-90 oil specifically designed for manual transmissions.

However, all they have in the States is their Syntec gear oil which is a differential oil. Some people has used it and say it's fine though.

quote:

Originally posted by Doug Hillary:
Hi,
I installed Castrol Syntrax 75w-90 GL5 synthetic oil throughout (transaxle/rear diff) my MY02 Outback 2.5 Manual when new and at around 200kms
The oil was not changed or topped up again

I recently sold this wonderful car with 130k kms on it. The gearshift quality was still "as new" (excellent) and the red Syntrax was still clean (blotter tested) and clear

Regards
Doug


 
Hi,
SilverGGA - no, Syntrans 75w-85 (also sold as Syntrans M 75w-90) was Castrol's GL4 gearbox oil

Syntrax 75w-90 is GL5 and is a very popular transmission (transaxle) oil amongst racers (V8Supercars etc) - in the XH21 formulation it was exclusive to the Jaguar XJ220. It is used in Formula 1. It is the prime recommendation for the diffs in some high power Porsches, Subarus etc

I use it in my heavy trucks (500hp-60000kg GVM)
and run it out to 1m+ kms without changing

Since using these oils (from 1997) we have never replaced a diff part or bearing (only wheel bearings at brake overhauls - sometimes)

Regards
Doug
 
Hmmm. Referring to the shop manual, Subaru only recommends 80 weight gear oil for ambient temperatures under 86°F.

However, any GL-5 85 weight gear oil does meet their spec for higher temps.

 -
 
You are correct. I mixed up the Syntrans with their Syntrax/Multitrax line. Especially after seeing that your location is in OZ. I was trying to get my friend to ship me some Multitrax before using SF MTL-R
wink.gif


quote:

Originally posted by Doug Hillary:
Hi,
SilverGGA - no, Syntrans 75w-85 (also sold as Syntrans M 75w-90) was Castrol's GL4 gearbox oil

Syntrax 75w-90 is GL5 and is a very popular transmission (transaxle) oil amongst racers (V8Supercars etc) - in the XH21 formulation it was exclusive to the Jaguar XJ220. It is used in Formula 1. It is the prime recommendation for the diffs in some high power Porsches, Subarus etc

I use it in my heavy trucks (500hp-60000kg GVM)
and run it out to 1m+ kms without changing

Since using these oils (from 1997) we have never replaced a diff part or bearing (only wheel bearings at brake overhauls - sometimes)

Regards
Doug


 
I would like to interject that I have had excellent results with Motul Gear 300 full synthetic in my 5 speed Subaru. Some of my club buddies have put 50k miles on their trannies and have had no problems with Motul. Just my two cents. Brian
 
I'll add that in the handful of suburus I've worked on the factory fill lube is noticeably thinner than what the service manuals call for. Also seems to shift better than manuals spec'd fluid. One guess might be it's oiled for a great test drive experience?

Since suburu uses a hypoid gear to turn the power 90deg, I prefer a gl 5. gl 4 fine for the sideways mounted motors.
 
I've tried a few things. First was Red Line 75W90NS bought at a local speed shop; I believe Red Line calls that a "GL-5 type". Thought it was OK, but wanted to try something different. Then I got some Motul Gear 300 online from a motorcycle parts dealer. Stuff works pretty well - especially after a few weeks. It's still not smooth like a Honda manual, but I knew that when I got the car.

The hardest part was finding the T70 Torx bit to remove the transmission drain bolt.
 
Rise from your grave!

I'm resurrecting this thread to ask your advice on oil selection in 2010 (post SF). I've got an old Subaru, a 1994 Domingo. 60hp, baby. It uses the Justy gearbox, and had 80W GL-4 specced from the factory.

However, it's one of those finicky subaru gearboxes that has wimpy brass syncros, a hypoid gear train, and a plate-type AWD coupling all in the same transaxle.

Shifting was notchy when I bought it, and got worse after I put 75W90 Castrol Syntec in there. It's hard to shift sometimes, and double-clutching is mandatory.

One stock oil I found on the internet is:

Shell Gear Oil S 75W80
Viscosity 40C: 54.4
Viscosity 100C: 9.4 cSt/C
Viscosity Index 154
Pour point -39C
GL-3 (???)

Stock oils now are limited to the "Subaru Extra" 75W80 (not Extra S), recommended as a GL-5 with the "just right" balance of friction modifiers. Unfortunately it only comes in 20L pails.

Any other suggestions for a brass, hypoid, and LSD-friendly manual gearbox oil?
 
GL5 gear oils without LSD additive is what you want like MotulGear300, Eneos MTF, Silkolene Silktran, Idemitsu MTF, or Redline 75w90NS.

Valvoline has a GL5 mineral 75w90 pn vv820 is easy to find hopefully in local autopart stores.
 
Thanks, unDummy. I agree that the Castrol Syntec LSD additives are probably the cause of my [censored] syncro performance.

Why do you think the viscosity difference (80W vs. 90) won't matter? And will I risk any damage doing tight turns with no LSD additive around the AWD coupling?
 
The Redline 75-90 NS seems like a good bet, like undummy said.
It will actually be thinner when you need it, and thicker when you need it than straight 80.
Shifting should be improved. but it may take 500 miles to get up to speed.
Don't expect shifting miracles.

If it were mine, I'd consider that a lightly loaded hypoid gear may be well lubricated with a modern tranny /gearbox oil .
Esp a full synthetic. So I'd be considering MT90 or MTG.
 
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