Changing the transaxle oil in a Bus, Vanagon, or Eurovan is not easy—and even more difficult in 4WD (Syncro) Vanagon. Both the drain and fill plugs require a 17mm internal hex (“allen”) wrench or bit (GoWesty offers replacement filler and drain plugs with an EXTERNAL 19mm hex! Yeah!). If you have such a tool, draining is a snap. However, re-filling can be tricky, on your back, with no way to pump the oil into the side of the transaxle. Just getting the filler plug out can be tricky, especially on a Syncro where you have to work around the skid bars. So, if you are not willing to buy a couple of tools (17mm bit and hand pump) and get a little messy, just take it to a shop. “But wait, I thought this article was about type of oil?!” Oh, yeah, right…
Up until 2017, we had been recommending MT-90 for Vanagon manuals because it is the only high quality, synthetic GL-4 oil available. GL-4 is what VW called for back in the ‘80s, when it was commonly available and the standard for many applications. Nowadays, the standard is GL-5, which is a superior lubricant. Gears and bearings just last longer with GL-5, plain and simple. So, why not switch?
Well, there has been some concern regarding the chemical composition of GL-5 that could result in harm to the brass synchro rings in the Vanagon transaxle, and/or that it was too slippery for the Vanagon synchro ring design and would cause shifting issues (grinding). These arguments never made much sense to me, as I have never seen a synchro ring that was not yellow brass and of the same conical design just like in every transaxle I have ever torn apart. In fact, even modern manual transmissions use the same design synchro rings, and all currently run on GL-5.
So, we decided to switch to a top quality GL-5 in several of our in-house Vanagons starting in 2015 - including our LeMons/NORRA race van - to try it out. We have found that they all shift no differently than your typical Vanagon manual with GL-4. Also, we have seen no evidence that the GL-5 has any effect on the material the synchro rings are made of, which is not surprising.
These test results, and discussions with transaxle parts suppliers, led us to switch from recommending GL-4 to GL-5 for all Bus, Vanagon and Eurovan manual transaxles, as well as the final drive sections of all equipped with automatic transaxle.