Use of GL-5 transmission fluid in GL-4 spec transmissions

Capt. Mike

Following transferred from archives.

k1cajun (

5/5/00 (6:17 PM)

Sorry for yelling . . . but elsewhere in these message boards, recommendations are made to use GL-5 gear oil instead of the VW specified GL-4 when changing transaxle fluid (standard trannies only). But this is wrong.

For manual transmissions, DO NOT use GL-5, only GL-4. There is a reason manufacturers don't use it in manual transmissions. It is a differential oil and should only be used in differentials. So the VW transmission is a transaxle - both transmission and differential? Still use GL-4.

Reason is, transmissions and transaxles have syncronizer rings and differentials do not. The syncro rings are made of brass or other alloys of soft metals. GL-5 has an additive that is fine for hardened gears but will corrode and shorten the life of syncro rings.

I put GL-5 in mine a short time ago. 800 miles later, it started dropping out of 4th gear while cruising on highways at speeds above 65mph. I checked linkage - no problem. Started looking into a tranny rebuild. Read in another website that GL5 is corrosive to tranny's. Checked out a couple of websites of gear oil manufacturers and they say so too. FYI, GL4 is also corrosive to trannies that call for GL3.

In my case, was it the reason I need a rebuild ? The rebuilder says not likely in only 800 miles. GL5 will cause a slow death. In my case, it was dieing anyway and at most, the GL5 just pushed it over the edge. But I'll never really know for sure . . ..

Capt. Mike

CAUTION: This reply is amended later in this thread.

5/7/00 (2:30 PM)

You're getting caught up in a very old wive's tale. GL-5 is OK for VW manual transmissions. In fact, you'll probably find 90% of the VW dealers use it. The subject came up again very recently so I went back to my source, one of the top lubrication chemical engineers for a major international supplier of both GL-4 & GL-5 as well as everything else including synthetics. National expert class. (His info also checks with their published materials manual.) This is the guy that investigated and supervised the lab tests of incidents that were claimed to be lube failures or damage. He says none were due to the GL-5 characteristics over GL-4.

First of all, if you are dropping out of gear, it has nothing to do with the syncros. It's worn gears, linkage adjustment or internal freeplay devloping.

There is nothing in GL-5 (or GL-4 for that matter that is corrosive.) In fact, both have the same anti-corrosive additives. (Try a litmus comparison test!) Also, there are NO brass synchronizers. Stop & think, real brass would wear out in a few weeks and is so soft it would dent or distort with the first few hard shifts. What you are seeing is an alloy that gives a gold-ish appearance. Probably a sintered iron &/or cadmium alloy to give it the friction characteristics desired. [A little side PS -- Porsche designed about 90% of the world's synchronizers and OKs GL-5.]

The difference between GL-4 & GL-5 is ONLY that GL-5 has an impact resistant additive. It was put in to prevent galling and to cushion the gear slap and impact every tranny has to a certain degree or another with acceleration & deceleration due to gear tooth clearance. The same characteristic of differentials. (By-the-way, VW differentials ARE VW transmissions, share the same oil, and have the same material spec gears.) I went out and re-read my stocks (Penzoil, Shell & MoPar OEM) just to be sure, and thay all say "Gear Oil", not differential oil -- in fact, GL stands for Gear Lubricant. (Hypoid is a style of gear cut found in both.) The MoPar is GL-4 yet all three are MIL2105D. The MoPar warns against using in other transmissions than their MoPar NV2500.

GL-4 meets MINIMUM specs and is why it's recommended. Just like DoT 3 may meet minimum specs for brake fluid, or SAE-SE (>'74 VW's) may meet minimum specs for engine oil. Engines & transmission evolve to put additional new strains on the lube, which call for additional new tehcnology lubricants. But with a few rare exception, the new lubes are backwards compatible. If GL-5 harmed trannies, you would have seen so many recalls, warnings and class-action law suits, your head would spin. Every factory manual and tech bulletin would be full of warnings. You don't say what year your Westy is, but I would hazard the guess that it's Type II or Vanagon, and GL-5 was just coming into general availability back then. Most manuals and specs were written for what was available then. Now, you'll be hard pressed to find it except in the discount or specialty lines.

I'm sure many distributors and sales departments want to justify why they continue to sell the GL-3's & 4's. And it's not that they are wrong -- I don't use the $10 super synthetic engine oils -- not because they are bad for my engine, but because they aren't worth the money -- diminishing returns for MY circumstances, but maybe not yours.

I'd hazard the guess that your tranny failure was totally unrelated. 800 miles is unlikely to create the wear or corrossion you claim. If it were common, how would most of us get hundreds of thousands out of a tranny. My '79 has had nothing but GL-5 and at 150K still hasn't got a clash. Mom's old Bug is at 158K without every being opened up. Their Vanagon is at 145K -- all original tranny. My current '90 4x4 Westy is 130K on the original synchros, as is my 31 year old Porsche. Definately not something that happens in 800 miles.

It's good to raise the question, but this one defies logic. Most of the incompatibilities are due to different techonologies (example - coolants) or different base product (example - DoT 4 & DoT 5 brake fluids), not due to the stepped-up supercession of technical specs within a line. Transmissions die from heat, contamination, lack of maintenance, and driving habits. They get moisture in them (through their breathers). An out-of-adjustment clutch will eat up synchros! Just routine gear wear ads to synchro strain. And everyone of us misses shifts and grinds the gears on occassion. Nothing is forever; synchros are actually a wear service item.
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Capt. Mike

Transferred and condensed from archives

k1cajun (

5/12/00 (3:11 PM)

First, I didn't say the use of GL-5 killed my tranny. In my post, I said I suspected it might and the rebuilder said not likely. That it would be over a longer time.

Just because the VW dealers use it doesn't prove GL-5 is OK. The dealer who did mine didn't even know what GL-4 and GL-5 were. I don't mean that they didn't know the chemical properties. They had not even heard of the codes. When I asked them what they put in, they had to check with NAPA where they got it and told me 80W-90. When I asked, "Yeah but is it GL4 or GL5 ?", they said "Huh?" (to paraphrase them).

As for class action cases, most of the driving public don't change gear lube in trannys or differentials unless there's a repair to be done. Class action lawsuits are brought by lawyers, not by regular folks and they do it where there are two factors: deep pockets and emotional dramas - like toxic waste, asbestos, tobacco, IUD's, breast implants, ... It's hard for a jury to feel a lot of emotional sympathy for a broken transmission.

If the auto manufacturer says it's a GL4 gear, they sell it new with GL4 and it's not their fault if an owner or dealer varies. The manufacturer said GL4. You could sue the dealer, but a single case is hard to prove and class action status would be pretty tough against a bunch of dealers scattered around the country. But all of that is just my opinion.

<copied from Pennzoil site>

2. What happens if API GL-5 gear oil is used in an API GL-4 gear oil application?

"API GL-4 and API GL-5 products typically use the same extreme pressure (EP) additive system, with the API GL-5 having about twice the concentration of a API GL-4. In service, these additives become active under extreme load and temperature when the protective oil film can be squeezed away. EP additives work by forming wear-resistant compounds with the metal of the gear tooth surface. As the gears mesh, these compounds shield the gear teeth from direct metal-to-metal contact that would cause wear and damage to the gears. If too little of the active additive is present, proper protection would be compromised. Too much of this additive could cause excessive chemical corrosion of the gear surface. If an API GL-5 gear oil is used in a application where API GL-4 gear oil is called for, chemical corrosion of "yellow metal" components may occur, such as bronze synchronizers, brass bushings, etc. This may lead to shifting difficulties or shortened equipment life."

So when some GL-5 product says it "exceeds GL-4" specs, it can be truthful in that it can withstand higher pressures. Does the API spec define a maximum corrosiveness ? Does the spec say that it applies to all metals ? By the way, when I said that the sync rings were bronze, I didn't say pure bronze - besides bronze is itself an alloy of copper and other metals and there are different bronzes. But when we say Corn Flakes, most of us know there's other stuff besides corn in it as well.

The thing is the EP additive bonds with the metal in a chemical reaction. Too much bonding IS corrosion.

I'm no chemist. Your source has published materials to dispute this? Are they online? Your buddy might be correct, but right now the sources I have recommend against it. For my money, there's no risk in sticking with GL-4.
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Capt. Mike

5/12/00 (9:16 PM)

:eek: OK, I stand corrected; your source IS published by a major manufacturer. My source was Texaco, their Z-1015 manual and my source's chemical engineering degree specializing in lubricants. Also his nearly 40 years experience as a top national troubleshooter. Their take:

"Multigear Lubricants EP are made from (base) & additives to provide excellent load carrying ability, EP properties, wear resistance, oxidation stability, anti-rust and anti-corrosion qualities and anti-foam. These products provide excellent protection against shock loading. In addition, they are compatible with other MIL-L2105B, C or D gear lubricants . . .." [Mil-L-2105D is GL-4.]

"They are recommended for makeup and complete refill of ALL passenger car & light truck conventional differentials, transmission, and steering gears."

". . . meets the performance requirements of and are qualified under . . . API Service Designation GL-3, GL-4 and GL-5."

So with that, & confirmed by the engineer, their GL-5 does supercede GL-4. A Shell book I once had said the same for their product. I hadn't given it a lot of thought since my Synchro is also a limited slip, thus GL-5 is even more appropriate. But I will back off saying ALWAYS use GL-5, even if calling for GL-4. I've used it continuously in every tranny & diff without a lube failure in what's wl over half-a-mil miles, but I also admit I change every 30K, more often in some, so nice fresh oil isn't likely to corrode anything.

I do hope you don't underestimate the admittedly slow and methodical culling of bad products by the dealer process or by the legal system. Manufacturers, with any slight bump in the warranty claims rate, tend to come down harshly on dealers that have deviated from their warnings -- witness those that tried the cheaper phosphate containing anti-freezes. More than one dealer ate the consequences, but it doesn't get a lot of press. Ditto the legal system. I'm as anti-lawyer as anyone, but as a veteran of 6 court cases (all wins), including a breach of warranty/lemon law suit against Mercedes-Benz and another breach of warranty against Chrysler, can vouch that a single win often sets a precedent and to avoid class action by ignoring it, they take corrective measures. It's not the class action, it's the threat of class action.

But I appreciate your RESEARCHED come-back. That's how we all learn. I've added that to the lubes post so other readers can make their own decisions. Thanks.
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Capt. Mike

Following is the response to a query to Shell Oil on the subject, whose GL-5 is listed as superceding their GL-4 for use in all transmissions in their product guide.

1. We recommend against the use of GL-5 oils in transmissions where GL-4 oils are recommended exclusively because of potential interference with the operation of the synchronizers. Our experience here is limited, so if we err, we err on the conservative side.

2. Where the OEMs take a strong stand on the use of only a particular oil, we do not argue when warranty is at stake. Even after warranty, we will not recommend alternative products unless we are sure they will perform up to the customer's expectations. In most cases, we recommend the customer should use the factory-recommended lubricant.

3. Congratulations on your good success with Shell oils. I can't help but wonder if a lot of the miles were on the famed ROTELLA T motor oils?

I took a quick look at your web site and was impressed with the sense of completeness there. I had a '73 VW van which was a lot of fun for about ten years - then I moved on to a larger vehicle as the family grew.

Thanks for your inquiry and interest in Shell products.

Ed Brown, for Shell lubricants

Gary B. Dixner

New member
After reading this thread I decided to have the unknowns drained from my manual transmission and have GL-4 installed. Amazing, some of the things repair shops will tell you including, "Use AT fluid" (Dexron III). Finally found a shop that knew the difference. GL-4 cost me $8.00 per quart but I feel a lot better. Thanks for all the info on this site and reasonable and open-minded debate herein.
I've been following this thread for awhile and it's now time to change the tranny fluid in my '90 Vanagon. I've decided to stick with GL-4, but I'm having a hell of a difficult time finding it in the recommended 80W/90. The nearest I can come is a gallon of Sta-Lube 85W/90 GL-4 down at the local Napa store.

Is it alright to use 85W/90? Any drawbacks? Any hints on where to find 80W/90 GL-4 in the Portland, OR area? Thanks for the help and happy motoring!

JOHN :confused: :confused:

Capt. Mike

Basically, yes. The original VW specs were for straight 90W but that has pretty well disappeared from the market except specialty lubes. Like motor oil, multi-weights have arrived in gear oils. The 80W-90 & 85W-90 will work well as they are able to handle the colder temperatures better but still give the protection of a 90W. Only if you are in extreme cold would the lower 80W-90 be required. Do NOT use the 80W-140 on the market; that is for other applications besides the VW type transmission.

*Sta-Lube is a generic level brand; you might consider the Red Line brand if you want a premium.

You can, of course, get the older GL-4 from dealers but at outrageous prices. Note the revised fill level in the Bentley page 35.60.

* Both brands are available on Amazon:

Red Line (premium brand)

Red Line (premium brand)
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New member
I just had the transmission fluid changed at a 76 station--is it ok to put in a synthetic 75-90 fluid? They said it was GL-4. I have an 89 westy and was told it was a good choice for transmission fluid. Any opinions? My van has 150K miles on the original 4-speed.


New member
I wouldn't just up an switch to a synthetic without draining and cleaning the system first.. even then I'm skeptical (I'd only do it on a new motor/trans).... but synthetic is the way to go, IMO.

Capt. Mike

I haven't seen any VW specs allowing 75W-90, thus I'd go slow. In what I presume is a hot climate (AZ), I think you may be going a little lite. Remember the characteristics of synthetic (described under the Oils topic in TIPS) is that the 90W required of VW is not achieved through viscosity, but through additives that "protect like." Thus a 75W-90, whether synthetic or not, might be a little thin. It might be worth examining in very cold climates, but regardless, synthetics do NOT allow longer change intervals in the VW, despite their hype and marketing.


New member
Since this thread is a little old, an update would be appropriate. You can hardly buy GL4 fluid anymore, especially in synthetic. GL5 can be used, but only if it has an MT-1 specification OR it specifically mentions GL4 compatible. The MT-1 spec apparently is compatible with the metals used in VW syncros.

pascal giasson

New member
Redline make a GL4 synthetic transmission/transaxle oil that many people use in their Vanagons. I have been runing their MT-90 for two years. In my 84 Westy I find it very smooth when the trans is cold but no noticeble difference from the old oil I took out when it gets to operatinig temps. I have 135 000 mile on my Westy.