This question comes up again and again. Each time there is someone who
quotes the workshop manual as gospel. Hans, please let me start by
assuring you that this is not intended to be directed at you personally.
Lubricating oils in particular have changed a tremendous amount during
the years since the factory let go of the job of updating the workshop
manuals. The manuals are an excellent guide, but do not offer up to date
specifications for modern fluids.
Castrol GTX in particular has changed significantly over the years and
is specifically formulated for modern engines and has the same
compatibility issues as any other main stream oil despite being a name
brand originally specified by BMC, MG, Leyland.
Luckily MG OD gearboxes are not overly sensitive to oil specification
and will run happily on a wide range of viscosities and additive
packages.
Personally I subscribe to the less is better approach and agree with the
recommendation of non-detergent single viscosity motor oil such as a
30-50 wt. Detergent oils have additives that do not do anything to help
lubricate the gears and may cause foaming which is an absolute no-no in
hydraulic control systems. The composition of these additive packages
did not exist at the time the factory manuals were printed.
Hypoid type gear lube is not necessary as the gears do not have high
loading, so the added "stickiness" just increases energy loss and heat
build up.
There are synthetics which according to the manufacturer will work
effectively with the OD clutch, but I do not have enough experience with
them to offer a recommendation.
Kelvin.
-----Original Message-----
From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net] On
Behalf Of Paul Hunt
Sent: Monday, October 09, 2006 1:30 AM
To: jello@ida.net
Cc: mgs@autox.team.net
Subject: Re: over drive oil
I'm not sure that is correct. I see oils specified for pre-1960
classics as
low-detergent (which implies to me that the norm *is* to have
detergent),
although detergent oils have been around since at least 1935. Others
such
as GTX are specified as having very efficient detergents for solublising
(their word) sludge and keeping it circulating until it is trapped by
the
filter or comes out the drain hole, i.e. it doesn't build up in the
engine.
There is no doubt that the factory specified the same oil for the
gearbox as
the engine in the MGB, including GTX. However there *are* additives in
some
oils which are detrimental to synchromesh and should not be used, these
include synthetic gear oils intended for limited-slip applications.
PaulH.
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