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<DIV><FONT size=2>Saying it doesn't need detergents (in this post) is completely
different to saying 'it needs to be non-detergent' which is what you said
earlier, and that is what I was questioning. MGA recommendation was
apparently (<A
href="https://mgaguru.com/mgtech/gearbox/gt107.htm">https://mgaguru.com/mgtech/gearbox/gt107.htm</A>) for
30wt non-detergent as that was commonly available at the time. All the
detergent does is carry any particles around until they are filtered out by the
OD (if fitted). It doesn't foam as is often claimed, dish washing liquid
foams from additives deliberately there to make it do that, who would buy a
detergent that didn't even if it was as effective as cleaning dishes? My
Laycock manual doesn't specify what oil should be used, that is left up to the
manufacturer of the vehicle and how it is intended to be used. All it
emphasises is that friction reducing additives should not on any
account be used.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Saying the multigrade properties of engine oil break down over
time in a gearbox may well be true, but it's a giant leap from there to say that
means 30 wt straight oil is somehow 'better'.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Do you have a reference for earlier models needing something
other than engine oil of 20W/50? My period WSM and glovebox handbook state
20W/50, although for temperate climates it also includes 10W/40 and
10W/50. Temperature ranges below that EXCLUDE 20W/50, and there are no
different recommendations for 'hot' climates i.e. specifying it HAS to be 20W/50
and nothing else.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>The V8 gearbox recommendation has always been SAE90 gear oil
for temperate climates, SAE80 for colder, and I have a BL document somewhere
that states this for the 4-cylinder as well (although according to the link
above it shouldn't be used in 3-synch gearboxes as they have brass components),
although others say that was rescinded. That's not a recommendation to put
it in an auto box of course, any more than not using it in auto
boxes is a statement of fact that you can't use it in overdrives, which is
another giant leap to nowhere. Whilst the gearing arrangements use the
same principle, the control is completely different.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>My understanding is that it is only very early non-OD
gearboxes that were splash fed, and only 1st gear at that, the others fed by a
helical screw pump, and all four gears are pump-fed on the 4-synch - lots
of info here <A
href="https://mgaguru.com/mgtech/gearbox/gt201.htm">https://mgaguru.com/mgtech/gearbox/gt201.htm</A>.
That's regardless of whether overdrive is fitted or not, although they share the
same oil the lubrication of each is completely separate. Originally that
source recommended not towing long distances with the rear wheels on the ground,
but he says since then he has towed his 150 miles with no problems - but the oil
level does need to be correct.</FONT></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>...</B></DIV>
<DIV><BR></DIV>
<DIV>The factory manuals specify “engine oil” for both overdrive and
non-overdrive transmissions.</DIV>
<DIV><BR></DIV>
<DIV>If you analyze that recommendation, you would conclude that the key
characteristic they are concerned about is viscosity. Analysis follows:</DIV>
<DIV><BR></DIV>
<DIV>Transmission oil does not have to deal with combustion blow-by or high
heat, so it doesn’t need detergents or protection from thermal breakdown. And
my personal take on it (though this is apparently highly controversial) is
that for transmission oil it is better to use a single-grade oil, as
multi-grade oils break down into the single-grade stock over time, and one
does not change the transmission oil very often compared to engine oil (or
ever, IME). It’s not that multi-grade would hurt; it is that its benefits, if
any, won’t last, and the single-grade base stock is equivalent to the lightest
grade in the rating; i.e. 20W50 breaks down into 20W.</DIV>
<DIV><BR></DIV>
<DIV>But some people will fly off the handle at the suggestion that 20W50 is
not ideal. Their logic goes something like this: “the manual says ‘engine oil’
for the transmission; for my climate it recommends 20W50 engine oil for the
engine, therefore 20W50 is the only correct oil for the transmission.” I
believe it is only the later model MGs that have this particular
recommendation (20W50) in the drivers handbook.</DIV>
<DIV><BR></DIV>
<DIV>Anyway, backing up a paragraph or two, to my mind there is a significant
difference between the standard transmission, which uses oil for splash
lubrication only, and the OD transmission, which uses oil as hydraulic fluid
with a planetary gearset, much like an automatic transmission. Automatic
transmissions are extremely sensitive to viscosity — I don't think you would
have much luck with 90W gear oil in an auto
trans.</DIV></BLOCKQUOTE></BODY></HTML>