In the last two years I have seen an interminable debate over which oil to
use in the MGB gearbox on the internet or in specialised magazines. I don't
know why I restrained myself to get the facts straight once and for all,
but here's what I learned -and know- and never saw published or posted. I
don'y mean to be pretentious. I just feel I know something many of my
fellow MG lovers don't.
1. Is engine oil the right choice? No! Engine oil has both the right
viscosity and coefficient of friction to allow good syncronisers action and
cold driving. But it offers very poor gear protection.
2. Is hypoid gear oil he right choice then? No! Hyoid oil offers very good
gear protection but it sucks when it comes to syncronisers action, cold
driving and, in some cases (1967 model year MGB and MGC and before)
syncronisers lifespan. On top of this, one should not engage the overdrive
for many miles after startup when using this type of oil, more so in cold
climates.
Since these two oil types are the only ones that have been available in the
last decades and since they both fail as excellent manual transmission oil,
one begins to understand the mess British manufacturers spread in owners
minds as to which oil to use. THEY KNEW NO ONE WAS REALLY RIGHT SO THEY
JUMPED FROM ONE RECOMMANDATION TO ANOTHER. MG, for instance, changed his
mind 3 times in the MGB years...
OK. But this a catch 22 situation for overdrive owners since one cannot use
synthetic oil either in overdrive gearboxes you may say. WRONG! Again...
THE correct answer to this is: one may not use synthetic ENGINE oil. Why?
Because it makes the oerdrive slips, as many know. But you have to
understand that what makes that oil slips is not the synthetic part; it's
beause synthetic engine oils use about twice the antifriction additives a
normal engine oil uses.
So, Mister knows all, what to do? USE A SYNTHETIC MANUAL TRANSMISSION OIL.
It offers the best of both the hypoid and engine oils without any of their
shortcomings. Red Line makes two excellent ones: the MT and MT 90. By the
way this company recommends the MT 90 for the MGB and MGC. And YES you can
put it in an overdrive transmission.
Now, at last, two facts I want to tell you:
1. NO, I don't have any interests in the Red Line company; I am a poor
screenwriter... And French...
2. For those who would like to know in more details why engine oil is NOT
good for the MGB, here's one more hint that I hope will end that vintage
oil suspense debate: modern engine multigrade oil contains thickeners:
those allow the oil to ticken as the engine temperature rises. BUT those
thickeners, for complex reasons, DON'T last well in a gearbox. After 5 000
miles or so, and this applies only to a gearbox, the thickeners fall apart
rapidly. Result: you have almost no gear protection after a year or so...
Sorry if I ever made some english writing mistakes. I'm supposed to be a
perfect bilingual but, hey, I'm no Sheakespare and french is still my big
love...
More of the Final word serie to come, IF the response is positive. I have
some secrets to share concerning the gearbox reliability, the octane and
pre-ignition debate, and some thoughts concerning the MGC.
Best wishes to my american mg comrades...
Pierre Racine, CANADA.
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