Tim asks:
| 1) are engine oil and gear oil rated so differently that 50w in one has
| similar viscosity to 90w in the other?
Yes. As most people know, "x weight" is just an index into a table
whose entries are viscosity ranges. In the case of motor oil, there
are multiple tables, one for cold temperatures and one for hot.
Measured in centistokes, they differ by a factor of about a thousand,
if I recall. Gear oils use entirely different tables, so no viscosity
relationship can be inferred by comparing 'weights' of engine vs gear
oil.
This topic came up on rec.autos.tech a while back, and I believe it
was mentioned that 50 wt motor oil and 90 wt gear oil are, in fact,
similar in viscosity.
An interesting tidbit along those lines is that the Lamborghini Miura
combined its sump and gearbox. I have heard it said that it did not
work out; the 50 wt motor oil specified was too heavy for the engine
and the additives in the oil were inappropriate for the gears. The
last (SV) model got a dry sump, and neither Lamborghini nor anyone else
has used the idea since.
Now, back to cars we can afford ...
Dave Van Horn
|