Transmission oil

alpine4

Active member
Joined
Aug 15, 2019
Location
Victor, Idaho
TDI
2012 Audi A3
My friend is getting his manual transmission oil changed for his 2005 Jetta TDI. Mechanic is recommending GL5 rated oil. That seems wrong! Or am I wrong?
 

Powder Hound

Top Post Dawg
Joined
Oct 25, 1999
Location
Conkud, New Hampshiyuh, USA
TDI
'00 Golf 4dr White 5sp, '02 Jettachero 5sp, Wife's '03 NB Platinum Gray auto(!)
The story is that GL-5 supposedly is detrimental to yellow metal parts (bushings, synchronizers, possibly shims) because the extra pressure additive is molybdenum disulfide. MoS2 is great stuff as it works with pressure and does not require heat to plate the moly onto the wear surface and thus prevent wear. When this happens, the sulfur is released and can combine with the copper in the yellow metal parts. That is where the corrosion happens. Or maybe it is just a tale from 60-80 years ago, and the chemistry is better these days, but the old story won't die. Kinda like driving real easy during engine break-in.

GL-4 lubes are "better" because the amount of antiwear additive is lower. You can tell because it doesn't stink so badly as GL-5 lubes.

Some people dispute these findings. I have read anecdotal information on this site where a german engineer, when asked about this directly, said the GL-5 restriction was not necessary and their (VW's) transmissions could do fine with GL-5 lubes. Since it is anecdotal, it is merely a story and there is basically no weight behind it. But some people will claim worrying about GL-5 vs GL-4 is a waste of worry energy, and others act like you are committing sacrilege to use GL-5 in your VW transaxle.

So you can run an experiment, or you can just use only GL-4 and relax. It all really depends on how risk adverse you are, and whether you think the transaxle is already compromised or not. I guess.

If you decide to use a GL-5 lube, make sure the viscosity is down where it needs to be for the climate in which you live. Up here in New England, it is still quite cold in the winter despite global warming, so most viscosities that are available in the GL-5 category aren't appropriate anyway. So make sure that you get the right viscosity no matter which way you decide to go.

Personally, for my car, Redline MTL works great, and did so when I was in Phoenix as well. There's a little thicker version available which probably would be better for a hot climate like Phoenix, but MTL works well in either place. Lots of users here like Synchromesh (various sources, probably all made by the same Pennzoil facility), and there are some who will claim if you don't use the prescribed VW lube, you are risking (best not described here - this is a family show after all) failures. Up there in Idaho, I'd be very careful about a GL-5 lube's viscosity.
All the above mentioned lubes (MTL, Synchromesh, VW's) are described as quite thin. Please bear this in mind, or the transaxle that works so well now might sound like it is trying to chew itself to death come Thanksgiving. So.

Just think about what you (or rather, your friend) would like to do and go for it. Don't use what the mechanic wants to get rid of - use what will really work and is really recommended based on the application, not stock levels.

Cheers,

PH
 
Last edited:

DieterLange

Active member
Joined
Jul 19, 2020
Location
Brisbane, Australia
TDI
2004 Mk5 Golf 2.0 TDI
How often should you change your transmission fluid? I don't think mine has been done in a long while or more likely never done at all (my cars at 205,000Km)
 

alpine4

Active member
Joined
Aug 15, 2019
Location
Victor, Idaho
TDI
2012 Audi A3
Update my buddy put in GL4 rated fluid in the transmission and now Jetta shifting 10X smoother and better the ever before. He used syncromesh fluid.
 

tikal

Veteran Member
Joined
Apr 18, 2001
Location
Southeast Texas
TDI
2004 Passat Wagon (chainless + 5 MT + GDE tune)
alpine4, here is another option, perhaps a little bit more work upfront but worth it for another 100,000 miles or so in my view:
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After approximately 100,000 miles using BG Syncro Shift II I wanted some overall improvement so my research lead me to going with this formula:

I used the new Redline MT-LV fluid mixed 50/50 with Superlight Shockproof.

One of the TDI gurus recomends mixing the factory 02J fluid with Superlight Shockproof so that is also an an option.

The Superlight Shockproof really improved the notchiness with higher mileage gearboxes. It was very noticeable.
My TDI specialst did the transmission fluid change in my manual five speed 2004 Passat in May 2020 and so far I am very satisfied (it took closer to three quarts total). The shifting feels more solid overall in this summer and I get easier into first gear which was, at times, difficult to get into for some reason. More of the discussion in this thread.
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Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
the only thing i use
the best
I flushed it by doing a 2nd change on the next oil change 10K later. the fluid i pulled out was nasty AF almost as bad as the fluid i pulled out that was clearly never changed once in the cars life. took a sample after the flush, SO CLEAN, SO NICE. i highly suggest you do the same. wait 10K and change it again! you can use a straw method of pulling a little bit out to see how nasty or nice it is before committing to a 2nd drain and fill.
 
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