Mark:
Thank you for the succinct response. I was trying to compose something
similar and gave up.
Much of the arguing about what oil to use is based on the misconception
that 90W gear oil has a lot higher viscosity than say 20/50 engine oil
and will jam up the gubbins of the transmission. It won't.
There are a lot of variances for each type of lubricant, but the
differences are more subtle than most people understand.
Kelvin Dodd
> -----Original Message-----
> From: mgs-bounces+doddk=mossmotors.com@autox.team.net [mailto:mgs-
> bounces+doddk=mossmotors.com@autox.team.net] On Behalf Of
> mark.jones@exxonmobil.com
> Sent: Wednesday, August 15, 2007 11:37 AM
> To: mgs@autox.team.net
> Subject: Re: [Mgs] Overdrive oil
>
> The viscosity and other properties of 20W50 motor oil and 80W90 gear
oil
> are very similar. At 40 C (104 F), 80W90 gear oil (Esso Marvelube)
has a
> viscosity of 149 cSt and 20W50 motor oil (Esso Extra) is 153 cSt. At
100
> C
> (212 F) gear oil is 16 cSt and motor oil is 17 cSt. Density (887 vs
880
> kg/m3) and pour point (-30 vs -24 C) are also very similar.
>
> The reason for different weights, 20W50 compared to 80W90, yet similar
> viscosities at given temperatures, is because gear oil and motor oil
have
> different grading systems.
>
> So use either 20W50 motor oil or 80W90 gear oil in your MGBs
transmission,
> either will work fine, at least that's what I believe.
>
> Mark Jones
> 73 MGBGT
> 80 Spitfire
>
> From: Bob Howard <mgbob@juno.com>
> Subject: Re: [Mgs] Overdrive oil
>
> Why would anyone use 90W gear lube....?
>
> MG at one time issued a Tech Service Bulletin that said 90w could be
> used. About a month later that TSB was rescinded, but that bad
> information
> was picked up and used in some service manuals published by others. I
> have
> an old Haynes that shows 90 as an approved lubricant. It came with an
> OD-equipped MGB when I bought the car. I changed all fluids as soon
as I
> got the car, including changing to 90 from whatever nasty sludge was
in
> the
> OD at the time, and it worked fine until air temp dropped below about
> 60degrees F.
> Sad to say, that erronious information is still out there in some
old
> books.
> Bob
> _______________________________________________
> doddk@mossmotors.com
>
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>
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