Hi,
I'm about to do a diff and gearbox oil change tomorrow and was looking through the manual at which oil to use (turbo 2000, 1999 model).

75w-90 is listed as suitable for all temps for use in the gearbox, but I noticed that for the rear diff it recommends 80w-90.
Is there a major difference between the two oils? I have 5 litres of 75w90 sitting here which should be enough for the gearbox and a bit left over, I was hoping to get away with using the remainder to do the diff with.
Is there any major reason why I should go out of the way to obtain some 80w-90 for the rear (the vehicle is quite high mileage - around 95k)?
The cost of buying more oil is unimportant, but having to make another trip to the auto store is going to delay the work by a week and I would prefer to get it all done tomorrow.

Any advice appreciated, thanks!

 

75w90 will be perfectly fine in the rear diff of a std UK car