Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!

[Philnewbike]

Two other comments.   First, I find it amusing that we are supposed to take as received wisdom the comments of some engineers at Getrag  Fair do's, you go your way and I'll go with the gearbox engineers .   But if you read the cited article, they are being interviewed in the context of explaining why BMW gearboxes suck today, and have always sucked.  Phrases spring up like “who is guilty for creating this miserable transmission?”  Why am I supposed to treat their recommendation of 90 weight as gospel? No one said gospel, but in a choice between using X because you think it'll be better and the gearbox/oil engineers saying use Y, I'd personally go with Y, but you can do as you wish

Second, what are we to make of Guzzi specifying in their owner’s manual the use of 85W-140 oil in the gear box (and final drive) for the 1987 V75?  I bet that’s basically the same gear box as on any splash drive small block. I already explained the possible reasons for this earlier and also explained that this grade is fairly close to 90 anyway...

Again, I think we are probably reading way to much into a spec in the manual.   But I could be wrong about that and am happy to learn.  Yep, I think you're wrong lol but this is just for interest so as long as the box is wet I'm sure it's a lot better than dry 

[Philnewbike]

Thank you for the reply Phil please don't think I'm picking at your method I'm not, I'm just trying to pick up as much data as I can.

I was an egineer before I retired although competent on a good day was about my best effort.

If you are interested go to the 3rd post down on this page from the top where I listed Walther's Equation, but more to the point is a link to what (IMHO) is a pretty good paper on testing and gives a breakdown of the various calculations that can be used to interpolate (or extrapolate) oil viscosity at given temp

Many thanks for your efforts and your replies it's appreciated

John

Hi Old Jock

Not at all, your thoughts are very interesting, I just haven't got the patience to learn a new formula (not yet anyway)!

best wishes
Phil