I use 20W50 motor oil in my GT's overdrive gearbox, but in my other British
Leyland car's overdrive gearbox I use the recommended 80W90 gear oil
(synthetic actually, going on 6 years now). I have not had a problem with
the operation of either one of them. Volvo recommended gear oil in their
overdrive gearboxes. Use whichever one you want to, either motor oil or
gear oil, traditional or synthetic, they both will work fine in my opinion.
I really can't see detergent motor oil foaming in the gearbox, I would
think that there is more of a tendency/possibility for oil to foam in an
engine than in a gearbox. From what I have read motor and gear oil both
have additives to minimize foaming.
Here is something I found on Imperial Oil's website concerning their
Marvelube Product
(http://www.imperialoil.ca/Canada-English/Files/Products_Lubes/IOCAENCVLESMarvelube_80W90.pdf)
stating that a 80W90 gear has the same viscosity rating as a 20W50 motor
oil:
"MARVELUBE Gear Oil 80W-90 is a straight mineral gear oil recommended for
API service GL-1 applications. API service GL-1 is defined by the American
Petroleum Institute as designating those non-EP gear lubricants suitable
for the lubrication of automotive spiral-bevel gears, and some manual
transmissions operating under mild conditions of low unit pressures and
sliding motion. MARVELUBE Gear Oil is primarily recommended for use in line
haul truck transmissions because of its ability to withstand continuous
high temperatures better than EP type gear oils. It is also preferred to
heavy duty engine oils because of its 80W-90 shear stable multi-grading,
which provides the operating temperature protection of a SAE 50 grade
crankcase oil and the low temperature performance of an SAE 20W fluid."
Mark Jones
'73 MGBGT (w/OD)
'80 Spitfire (w/ OD)
From: "dannyvarnado" <dannyvarnado@cox.net>
Subject: Re: [Mgs] Overdrive oil
I was told by the transmission re-builder that it would be best not to use
"detergent oil" in the overdrive transmission because foaming, typical to
detergent oil, in the overdrive section could be detrimental. I've never
had a problem buying name brand non detergent oil at my local auto parts
store.
Danny V.
'58 MGA daily driver (w/OD)
'76 MGB V-6 project
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