Using a GL-5 in a GL-4 spec transmission

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According to this article it is not a good idea to use a GL-5 fluid in a transmission designed for GL-4

http://www.widman.biz/uploads/Transaxle_oil.pdf

Are there any exceptions? Is there some new technology that makes GL-4 obsolete?

My Fiat's gearbox is spec for a GL-4. The (1998) workshop manual states to use Fiat's own "Tutela ZC75 synth" which at the time was a full synthetic 75w80 GL-4. However if you go to the dealer and buy this oil it is now a GL-5. I believe Fiat changed the spec of the oil from GL-4 to GL-5 at some stage after 1998.

So is it OK to use? My gearbox does have soft metal syncros. Is it possible they have formulated the GL-5 fluid with additives that are not detrimental to soft metal syncros?
 
My understanding is that gl5 is a no-no... My jeep's transmission was speced gl4 and now they recommend 5-30 Mobil 1 motor oil.
 
I would say yes, you should use GL-4 in a transmission spec'd for it especially if an older one.

I have use RP maxgear GL-5 in trans spec'd for GL-4 with no troubles before. But overall I think it feels much better using proper GL-4 gear oil. Redline and Amsoil both make excellent GL-4 gear oil.
 
NEVER use GL-5 where a GL-4 is specified by the manufacturer!!

The reason why is that yellow metals (like brass) are used in the GL-4 units and that GL-5 fluid can corrode or pit those softer metals. Don't let ANYONE convince you otherwise, including the dealer, USE EXACTLY WHAT THE CAR MAKER SPECIFIES IN YOUR MANUAL IN THIS CASE!
 
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Originally Posted By: dbassk1ng
My understanding is that gl5 is a no-no... My jeep's transmission was speced gl4 and now they recommend 5-30 Mobil 1 motor oil.


The dealership tried to sale me on that [censored] also, I hope you didnt put 5-30 in your gear box.........There are VERY severe differances between a motor oil and an EP gear lube.

I use AMSOIL manual tran fluid it's a GL3/4 spec in all my AX-15's(brass synchro's), works like butter !
 
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Originally Posted By: antiqueshell
NEVER use GL-5 where a GL-4 is specified by the manufacturer!!

The reason why is that yellow metals (like brass) are used in the GL-4 units and that GL-5 fluid can corrode or pit those softer metals. Don't let ANYONE convince you otherwise, including the dealer, USE EXACTLY WHAT THE CAR MAKER SPECIFIES IN YOUR MANUAL IN THIS CASE!


this is true but modern gl-5 are buffered so this isnt the problem it used to be.

that being said the extra additives can adversely affect shifting.
 
Originally Posted By: Rand


this is true but modern gl-5 are buffered so this isnt the problem it used to be.

that being said the extra additives can adversely affect shifting.



Can you elaborate on that please?
 
For what it's worth:
10 years ago I used GL5 in the differential of my Triumph, that requires GL4, At the time I thought "what the heck"
Within three years (and not many miles) I was experiencing a lot of back lash in the drive shaft (it was killing my UJ's)
When I drained the diff the oil was Green!
When I dismantled the diff the copper alloy thrust washers on the Crown wheel and Planet gears were NON EXISTENT, GONE! NOT AT TRACE!
 
I would only use GL-4 is that's what is specified. When I had my 05 Hyundai Tiburon, I went to several different stores before I found Amsoil GL-4 75W-90 at Napa. They all tried telling me the same thing, that GL-5 supercedes GL-4 and it would be fine to use in my transmission. Of course,they all got real defensive when I told them they didn't know what they were talking about.
 
There are GL-5 lubricants that also meet a spec of MT-1.

API Category MT-1 designates lubricants intended for non-synchronized manual transmissions used in buses and heavy-duty trucks. Lubricants meeting API MT-1 provide protection against the combination of thermal degradation, component wear, and oil seal deterioration which is not provided by lubricants meeting only the requirements of API GL-4 and API GL-5.

So the question becomes if buses and HD trucks somehow contain a different metals/materials set than automotive and light truck ones do...

Because if not, theoretically the metals issues have been resolved when this spec is carried.

Likely as was said above, they are buffered so it is not an issue.

And Ive read that the additization in GL-5 lubes is better.

Still it is a good option to utilize the spec that was designated for the part.
 
Originally Posted By: Rand


this is true but modern gl-5 are buffered so this isnt the problem it used to be.

that being said the extra additives can adversely affect shifting.



I wouldn't believe this for ONE second.

A lot of fluid makers can claim a lot of things, why risk it?

Use the specified GL-4 where a car maker calls for it. NOT WORTH TAKING CHANCES.
 
Quote:
And Ive read that the additization in GL-5 lubes is better.


The additive package in a GL5 differental lubricant is much different than the additization for an Application Specific MT lube with a GL4 protection rating.

The two major differences are in the AW additivies and the friction modifier additives.
 
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Originally Posted By: antiqueshell
NEVER use GL-5 where a GL-4 is specified by the manufacturer!!

The reason why is that yellow metals (like brass) are used in the GL-4 units and that GL-5 fluid can corrode or pit those softer metals. Don't let ANYONE convince you otherwise, including the dealer, USE EXACTLY WHAT THE CAR MAKER SPECIFIES IN YOUR MANUAL IN THIS CASE!


Except that GL4 has the same destructive sulfur as GL5. [Only 1/3 or so as much.]
Most [either type ] is buffered nowadays, and the corrosion is pretty much castrated.
My point is that GL4 has the same brass eating component as GL5.

So what to use? Go get Amsoil or Redline's offerings, tht are dedicated manual trans lubes. The Ford full synthetic manual trans lube is also superb.
 
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All the Redline and Amsoil transmission oils are GL4 too

I went to the shop and they had 2.5l of this on the shelf for a reasonable price so I bought it Penrite SIN Manual Trans

For some reason it is much cheaper than the GL5 version and about 1/3 the price of 3 quarts of Redline. I

I noticed it has no sulfur smell, is that normal for a synthetic gear oil?
 
Originally Posted By: mechtech20


Except that GL4 has the same destructive sulfur as GL5. [Only 1/3 or so as much.]

.


And the reason why the car makers specify the GL-4 is for just that reason, the parts were engineered to withstand that amount of negative residue from sulfurous byproducts..but no more than that. So essentially the parts subject to
GL-4 as the manufactures specify will suffer NO ill effects for hundreds of thousands of miles.

Can you show me a non premium GL-5 product that clearly states that is will NOT damage yellow metals used in gearboxes that specify GL-4?

I'm not interested in spending a lot of money for gear box oil, you shouldn't have to anyhow.
 
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I've been using GL-5 in all my old VWs and Dad's '76 Dodge van for years. No issues.

Primarily Valvoline and Lucas brands.

edit: And Dad's '85 Mustang.
 
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My STI tranny shares its sump with the front LSD, and calls for GL-5. GO's, like Motul Gear 300, are dual-rated GL-4/5, making it an easy, albeit expensice choice if yellow metal corrsion is too much of a concern for you. I'm going to swap out for Redline's 75W-90NS some time soon, just to see whether it helps with shifting.
 
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