Illustrations by Sarah Young
Three topics that always prove to be controversial: religion, politics and motor oil.
We can’t help with the first two, but we do know about oil–or, more accurately, we know people who know about motor oil. So we queried their scientific brains on the subj…
Two questions.
1. Several times references to the first viscosity number and "cold" temperatures appear in the answers. Assuming that cold does not apply to engine temperature but does apply to ambient temperature, what temperature is considered "cold"?
2. My MGBs use motor oil in the transmission. Is full synthetic oil suitable for my transmissions?
The “cold” viscosity number is determined via SAE standard J300. My understanding is that the temperature is measured at various points. (It’s never an easy answer, is it?)
The “hot” viscosity number measures the oil’s rate of flow at 212 degrees Fahrenheit.
For the second question, we got with Carl Heideman at Eclectic Motorworks:
The answer to the 2nd question is that non-overdrive MGB gearboxes last forever with conventional motor oil and we haven't seen benefits to synthetics. We have seen overdrive gearboxes be very fussy about oil and wouldn't recommend synthetic.
David, excellent article. Thank you, Kevin O.
I think Carl is right on with his advice on oil for OD trans - I raced two cars that used Laycock OD units and I always ran straight weight dino-oil and had no problems but some of the guys that tried synthetic in Austin Healeys and such had problems.
And BTW, although many say never race with a Laycock, the reason for doing so is that using a low ratio diff for acceleration (I usually ran 4.3 or 4.55) and a close ratio trans requires that you have a longer top gear which the Laycock does perfectly and you can baby it and shift in gently only when you are near red line in 4th normal on the straights. An excellent result given that when I was running vintage, they didn't want modern 5 and 6 speed boxes grafted in.
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