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 VW T25 T3 and Syncro Gearbox Oils

Gearbox oil gets a really hard life, engine oil has it easy. However when I ask people when was the last time you changed your gearbox oil replies often range from never to 5 years. Now what you say to someone who said that about their engine oil!  VW in their wisdom 30 years ago stated that the oil doesn’t need to be changed for the life of the vehicle. Unfortunately, for us, VW classed the life of the vehicle as 10 years, they didn’t expect us to be still driving around in them 30 years later, Be kind to your van and change your gearbox oil like you would your engine oil.

VW T25 T3 and Syncro Gearbox Oils gear oil

Which oil to use in a VW T25 T3 gearbox?

One of the most frequently asked questions about the  VW T25 T3 and Syncro Gearbox is which oil to use.

According to VW for the early 4 speed 091 4 speed gearbox VW recommend SAE 80/90W GL4 and 3.5 litres.   The later 4-speed gearbox from 1985 091/1 (DU or ABD), one should use SAE 80/90W GL4. Petrol’s hold 3 litres gearboxes and  Diesel gearboxes 4 litres.   5-speed gearboxes produced after this, use the same spec oil SAE 80/90W GL4 and 4 litres.

Which oil to use in a VW T25 T3 Syncro gearbox?

VW recommends SAE 80W GL4 for the Syncro gearboxes, and the gearbox takes 4.5 litres. 1.5 litres of oil are trapped in the gearbox so it is only possible to change 3 litres normally.

For the  Syncro front differential, VW recommends SAE 80W GL4 and to use 1.5 litres.

VW’s standard manual gearbox oil is 75/90W GL4 so as such the current thinking is to use 75/90W GL4 for the standard syncro gearbox. Non-standard transmissions for TDI vans or those doing a lot of hard work have been recommended to use 75/140W GL4.

Most Motorfactors will have a relatively cheap 75/90W  or 80/90W GL4/5 or GL4 gearbox oil which if changed every year should suffice.

Can I use GL5?

The VW T25/T3 and Syncro Gearboxes are not suited to GL5 spec oils.   GL5 oils have a detrimental effect on brass components in the gearbox i.e. it erodes them! Therefore GL5 should not be used. Oils that are marked GL4/5 can be used.

Should I use Molyslip in my gearbox?

Molyslip GM6RA is a good additive to use to help extend the life of your syncro rings and to generally give the gearbox any help it can. One dose every two changes is probably enough.

Hope this information is of help Paul


This Post Has 9 Comments

  1. Tom

    Old husbands tale. GL5 was reformulated early in its life to be non-corrosive thus usable wherever GL4 was specified. And its been many years, plenty of time for proof One way or the other. The lack of corrosion problems strongly suggests that concerns are false, right? And if theres no corrosion then GL5 is actually better due to its higher film strength.

    1. paul

      Interesting point thanks Tom

  2. Tom

    “the gearbox takes 4.5 litres. 1.5 litres of oil are trapped in the gearbox so it is only possible to change 3 litres normally.”

    If you raise the front of the van 10-12 inches the whole 4.5L will drain out. It is a shame to pre-contaminate your new lubricant with 1/3 of the old metal-infested oil. For longest bearing life, you want to get all the metal-polluted oil OUT. Metal in your oil is like a grinding paste. Think of it this way – any metal in your oil causes meta-to-metal contact, thus generates MORE metal in your oil. Not good. These trans are so rare and expensive it’s worth a “extra” effort to keep the lubricant clean.

    1. paul

      Good tip Tom thanks. I agree totally the cleaner you can get your oil the better and regular oil changes will help to solve this and also allow you to monitor how your box is performing thanks again Paul

  3. Ilija

    Which is the best oil for vw t3 syncro gearbox [4+G] and front differential? Is it best 80w90 gl4?

    1. paul

      75/90 GL4 or GL4/5

  4. Dave

    75w80 front diff 1.5l
    75w90 gearbox 4.5l
    synthetic or minral ?

    1. paulg

      Semi synth is generally whats out there or you can use synthetic once its good quality. Personally i think the frequency of changes is most important

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