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Transmission Oil

Subject: Transmission Oil
From: (Graham McCann)
Date: Fri, 28 Jul 1995 13:22:16 +1000
Having had everyone leap into the air on this subject let me take it a
little further.

First of all, however, soem of you miised the fact that 80W/90 gear oil is
only specified for the MGB GT when fitted with a V8 - which was an option
from 1973 to 1975 and in ALL cases the recommendation was 80W/90.  I have
three V8s and use that oil in all of them.  For my four cylinder MGB I use
engine oil.

When I approached Castrol requesting an opinion about why there was a
difference (and it was from its reply that I learnt that 80W/90 was
"thinner") the reply was a bit cagey as the did not want to refute a
manufacturer's recomendation.  The reply went on to describe the different
properties needed in a gear oil to an engine oil and it is not difficult
appreciate why the requirements are different.  For example a gear oil needs
very little detergent action since there is no polluton from gases etc.and
has to be very non foaming. However, the oil does need to adhere to metal
faces on gears and withstand very high temperatures caused by the friction
in a gearbox under high loads and so is made for the task. It is probably
the latter consideration which made MG specify it for the V8s but never for
the four cylinder models right up to the end of production.  I would suspect
that MG believed it had a good selling point in the convenience of the same
oil in sump and gearbox - regardless of the good engineering sense which
might have indicated otherwise.

To the correspondent who believes the gearbox will fall out of my cars from
using 80W/90 let me assure him that it has not and, if the experience of
1,500 MGB GT V8 (the number believed to be left from the production of
2,500) owners is to be believed, then it will not.


Graham McCann  Rivett, ACT. Australia
06 2889055

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