Golf MK3 8V gti gearbox oil? Which one to use?

[GOLF-MK3-GTI]

As above just got my old box re-con'd, I'm wondering what oil would be best to use?

Thanks

[AGGGTi]

Abit of over kill on an old 8 valve box but i used fuchs 75w90 oil and got it off opie oils, pricey but seems to be pretty good and my box was out of a 150k car and its spot on 

[GOLF-MK3-GTI]

The gearbox specialist who built my gearbox, said put 10w 40 in, but put loads of it in, I said are you sure? He replied yes. Make sure you put loads of it in. 

any ideas?

[AGGGTi]

Never heard of that before  ! My old box was a previously rebuilt unit and it was spewing a never ending trail of oil wherever it went, from every gasket and seal going, which makes me believe it had been seriously overfilled, so i cant see alot of the wrong oil being good! Personally id get 2 litres of cheap 75w90 run it 1000miles, dump it out and fill with good quality stuff, but i may be wrong?

[DCmk3]

Well this is slightly ironic, just yesterday I was looking for what oil to use in my gearbox.
What is listed is 2 Liters of 75W/90 Synthetic oil for those boxes.
Although I am running 80W/90 which has seemed to ease the gear changes during cold mornings.

10W/40 will be really thin, I have no clue why he would say run that, it's like water.
But if he insists you must run that and the box breaks, it's on him. 

[GOLF-MK3-GTI]

Spoke to mechanic whose piecing car back together this morning, he said yeah that's what I'm going to put in 10w 40, so I'm sticking to that now.

Only reason coz gearbox specialist has done Many of these gearboxes, I mean when I gvw mine in, he had another 3 golf gti 8v boxes to rebuild. And he has rebuilt gearboxes for me In the past. So he knows what he's on about.

And the mechanic eats, sleeps, sh!ts VW golfs  , so he knows what he's doing too. Let's leave it to the experts, I don't know if its wrong or right, but they know more than I do so I'll leave it to them.

[itavaltalainen]

10w40 is engine oil, there is NO gearbox oil with that spec.

Although the viscosity of 10w40 at 100 degrees is similar to that of 75w90 gearbox oil (as they are different scales) it lacks certain additives and so on and will be "chopped up" very quickly in a gearbox (ask any original Mini owner where the engine and gearbox share the same oil sump!). Cold gearbox oil is MUCH thicker as 10w40 engine oil. Gearbox oil can also cope with the high surface pressure you have between the gear flanks in a gear box - engine oil cannot (not even VW 505.01 PD-Diesel engine oil).

Use 75w90 as is specified and fill to max level (i.e. up to the screw hole).

Have a read at this very good summary about viscosity classifications.
https://www.opieoils.co.uk/pdfs/tech-articles/Viscosity-classifications.pdf

If the mechanic still says 10w40 after this I would be surprised (or he wants to keep fixing it )

[GOLF-MK3-GTI]

10w40 is engine oil, there is NO gearbox oil with that spec.

Although the viscosity of 10w40 at 100 degrees is similar to that of 75w90 gearbox oil (as they are different scales) it lacks certain additives and so on and will be "chopped up" very quickly in a gearbox (ask any original Mini owner where the engine and gearbox share the same oil sump!). Cold gearbox oil is MUCH thicker as 10w40 engine oil. Gearbox oil can also cope with the high surface pressure you have between the gear flanks in a gear box - engine oil cannot (not even VW 505.01 PD-Diesel engine oil).

Use 75w90 as is specified and fill to max level (i.e. up to the screw hole).

Have a read at this very good summary about viscosity classifications.
https://www.opieoils.co.uk/pdfs/tech-articles/Viscosity-classifications.pdf

If the mechanic still says 10w40 after this I would be surprised (or he wants to keep fixing it )

So i went to see the mechanic yesterday, i asked why are you and gearbox man adamant to use 10w 40? he said because gearbox oil is to thick and using 10w 40 will help as its thin and will help lubricate alot better. He said too thick oil is not good, very thin oil I.E like water is not good. 10w 40 is just right.

[itavaltalainen]

read the link I posted last time
75w90 gearbox oil has a similar viscosity range as 10w40 engine oil (cold - talking -xx degrees gearbox oil is a bit thicker) however it lacks exteme pressure capability and the wear in the gearbox will be exponentially higher.

if not why would all car manufacturers not just use 10w40??