GL-4 vs. GL-5?

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I have not been able to get a consistent answer to this question from any of the oil reps I have talked to.
For years, I have always believed that GL-5 could not be used in a GL-4 application. I was told by several oil company engineers that the additives in GL-5 are not compatible with the brass and copper bushings in some GL-4-specific applications. So I have always stocked both, for liability reasons.
Now, I am told by a Valvoline oil engineer that their GL-5 is 100% compatible in all GL-4 applications! His explanation was that they now use 'inacctivated sulfer compounds', and that the fluid is now interchangeable.
However, my Mobil oil-guy says that he never heard of 'inactive vs. active', and says that I'm just being hustled.
Mobil says that their GL-5 is good in all applications EXCEPT manual transmissions that call for GL-4 only.
Oddly, they both told me that their GL-5 supersedes the GL-4. When I asked them how, since the GL-classification system is not a superseding system, they both told me that it IS a superseding system!
I have read in several technical sources that the GL-system is definately NOT a superseding system.
Now that I have all this technical support and knowledge, I am 100% confused!
Who's got the answer?
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It depends on the particular type of sulphur/phosphorus additive chemstry they are using....

Generally if the product is GL-5/MT-1 rated it is safe to use. The MT-1 rating includes tests to evaluate high temp performance of the oil on "yellow metals" inside transmissions/transaxles.

I've used GL-4/GL-5/MT-1 rated, 75w-90 synthetic lubes in VW transaxles for twenty years with no problem. These specifically call for GL-4 rated gear lubricants ....

TooSlick
 
Excellent! I have a question though. I understand(I think) the MT-1 description, but you say that you use synthetic? In my shops, for financial reasons, we 'gotta' go with the dino', if you know what I mean. Can the MT-1 rating also apply to dino, or is it only synthetic? Thanks for your help!
 
Tooslick, thanks for your help. Incidentally, the info that I get from these oil companies IS from thier oil engineers! I make it a point to NEVER ask a salesman a technical question.
The problem is that sometimes I think these oil companies put thier 'engineers' on the phone who are probably not senior engineers, but just 'phone personell' masquerading as engineers.
My suspicion is because sometimes when I ask them a technical question, not only do they not really know how to answer it, sometimes they don't even comprehend the question!
Thats why I think this site (I just found it recently!) is gonna' be a big asset to me!
Thanks for all your help! Kit.
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This is really more a matter of the additive chemistry than it is of the type of basestock, so yes a petroleum based 75w-90 or 80w-90, MT-1 rated oil should be fine as well.

You really need to check with someone who works for the company - ideally a lube engineer and not a salesman
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The answer to some of the questions is sales. They don't want to tell you to buy someone elses oils.
From my experiences, you can use the "buffered" sulfur/phos GL-5 products satisfactorily in most transmissions without problems. But there are some in some conditions that will self-destruct. One of those I've seen serious problems with is the ZF truck transmissions where it will burn up the syncronizers. That is why I have a GL-4 product and a GL-5 product in Sulfur/phos.
On the other hand, Delo Gear Oil does not use sulfur/phos, so the product is truely GL-4 and GL-5 and MT-1 compatable.
 
Hi,
Apparently Chrysler made a mistake in their literature, calling for GL-5 in their Jeep 5 speed manual transmissions.
On Jeep related forums, most people say to go with GL-4 Redline MT-90 manual trans lube.
I did, and it really does work better.
Also I drained the old trans oil in to a milk jug that I have used to drain engine oil into.
I was burning the old gear oil in my wood burning stove in the garage, and noticed the old gear oil had cleaned out the milk jug. It removed all the sediment and dark color form the plastic.
Can anyone tell me what happened here?
YOOPYJ
 
This is what Mobil 1 says about their product...not sure if it can be generalized:

Mobil 1 Synthetic Gear Lubricant is suitable for all automotive applications where lubricants meeting API Service GL-5, are recommended. It can also be used in rear axles where an API Service GL-4 lubricant is recommended. It should not be used in any transmissions requiring an engine oil or automatic transmission fluid, or GL-4 performance level.

It says, for Mobil 1, that their GL-5 fluid can be used in GL-4 recommended differentials, but not GL-4 trannys.
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For what it's worth...
 
When I changed the Tranny oil on the Toyota 5 speed I chose Valvoline because it specifically said on the bottle that it satisfied the requirements for GL-4 as well as GL-5. ( The Toy calls for GL-4)
No problems whatsoever. I noticed,however, that the Valvoline bottles no longer make that statement.
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I posed this same question to a Coastal lube engineer a while back. He said that most of today's lubes have a buffering agent added to prevent the damage to the tranny soft metals. The Coastal lube that I used was listed as GL3,GL4, and GL5.

If a lube was only specified for GL5, I would be hesitant to use it in a GL4 application. If it is backward compatiable, it should have the specs on the container.
 
It's really simple......no GL5 should ever go into a synchronized tranny...period. Follow what the manufacturer recommends in terms of GL rating. I like to use Redline MTL or their ATFGL4 depending if the tranny calls for gear or ATF oil.

Unsynchronized trannies live well and long on GL5, but probably only need GL3 to 4
 
quote:

Originally posted by Alex D:
It's really simple......no GL5 should ever go into a synchronized tranny...period. Follow what the manufacturer recommends in terms of GL rating. I like to use Redline MTL or their ATFGL4 depending if the tranny calls for gear or ATF oil.

Unsynchronized trannies live well and long on GL5, but probably only need GL3 to 4


My gearbox is synchronized with brass parts and it specifically calls for a GL5 lubricant.........(Renault gearbox)
 
Isn't the GL-5/MT-1 rating for synchro-less truck (bigrig/semi/18-wheeler) trannies?
Additive package shouldn't be right for a car tranny.

a dual rated GL-4/GL-5 would work fine in a car tranny but a true GL-4 might shift a tad better.
 
My new Toyota Corolla manual transmission specifies 75W-90 GL4 or GL5 oil. I have a mind to try Redline 75W-90 MT90 which is GL4 and wonder if any have experience with this gearbox/oil combination.
Roger
 
Quote:


It's really simple......no GL5 should ever go into a synchronized tranny...period. Follow what the manufacturer recommends in terms of GL rating. I like to use Redline MTL or their ATFGL4 depending if the tranny calls for gear or ATF oil.

Molakule would disagree. There is nothing wrong with the correct GL5 blend for use in a manual transmission as long as it is specifically blended for it. Actually, it is preferred.

Unsynchronized trannies live well and long on GL5, but probably only need GL3 to 4


 
Quote:


It's really simple......no GL5 should ever go into a synchronized tranny...period. Follow what the manufacturer recommends in terms of GL rating. I like to use Redline MTL or their ATFGL4 depending if the tranny calls for gear or ATF oil.

Unsynchronized trannies live well and long on GL5, but probably only need GL3 to 4




I would not find where to edit a message so I'll try again.

Molakule would disagree. There is nothing wrong with using GL5 in a manual trans as long as the fluid is specifically blended for such use. In fact, it is preferred.
 
Quote:


Isn't the GL-5/MT-1 rating for synchro-less truck (bigrig/semi/18-wheeler) trannies?
Additive package shouldn't be right for a car tranny.

a dual rated GL-4/GL-5 would work fine in a car tranny but a true GL-4 might shift a tad better.




No, it is not just for 18 wheelers.

Dual rated GL4/GL5 can be effectively blended for passenger car use to enhance synchro operation. Read the label and make sure it is specified for manual transmission use. If it is intended for differential use, it may very well be inappropriate for any manual trans use.
 
Even if the GL5 and GL4/GL5 dual rated products are "safe", which I think most are now. My experience has been that most of them are too thick for many GL4 spec'd boxes. They work, but don't shift as good as they could. The GL4 fluids seem work much better.
 
""Mobil oil-guy says that he never heard of 'inactive vs. active', and says that I'm just being hustled.""

get a new Mobil Guy that is lube 101.

bruce
 
Quote:


Even if the GL5 and GL4/GL5 dual rated products are "safe", which I think most are now. My experience has been that most of them are too thick for many GL4 spec'd boxes. They work, but don't shift as good as they could. The GL4 fluids seem work much better.




Again, it is important to use a fluid that is specifically intended for use in manual transmissions. It is also important to use the correct viscosity, and there is a big selection of viscosities for GL4 and GL4/5.
 
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