Recently my mk4 bacame hard to shift into 2nd on cold mornings. At 150K I decided that it was due a gearbox oil change and I hoped some new oil would help.
Local VW dealer charged an outrageous amount for the oil he had but couldn't advise what the recommended spec was so I put in a fully synth 75W90 GL5.
BTW does anyone know for definite if GL5 is ok as my Haynes manual doesn't specify. I've heard that GL5 has additives that can be corrosive to some metals but I dont know if its ok for VWs
I went ahead and change the oil. Of course had I thought about this I would have worked out that new oil is likely thicker than one that's been used for 10 years and 150K miles. So in all likelyhood the new oil was going to provide more gear drag and give my poor old synchros an even harder time!
And that's exactly what happened - now I have to shift from 1st to 3rd for the first 10 mins until the oil warms and thins a bit.
So I need a thinner oil for those cold mornings. But what to put in? The fully sync 75W90 is about as thin as you can get.
Some have suggested Redline MTL but that's a 75W80 so its the wrong spec - its no thinner when cold so I'm not convinced it is worth the expense of trying. It's also a bit thinner when hot so I'm not sure if that will result in increased wear.
I've ruled out a gearbox oil additive because they definitely don't thin oil and if it reduces the friction of the synchro rings it will make things worse.
Anyone have any success with helping cold synchro problems by switching to a specific gearbox oil? If you did what oil did you use. Please dont suggest VW's unless you know the exact brand as I expect all dealers sell different brands. Thanks
