In article , Dan Caster says...

Someone else may correct me, but I think that any oil will be good
enough for your application. That is I don't think you will notice
the difference between a 5 mm hg vacuum and a 5 micron hg vacuum for
degassing resins.

If a motor oil has higher vapor pressure constituents
those will be pumped away, possibly compromising the
lubrication qualities of the oil.

Oils in vacuum pumps have to seal, they have to have
appropriate vapor pressures for teh application, and
they have to lubricate - all of these at the operating
temperature of the pump, and without degrading over
time.

If I were him I would charge the pump once with a
reasonable quality vacuuum pump oil, and run it with
the gas ballast valve open as a rule, because he will
be pumping a fair amount of water vapor and also whatever
comes out of his epoxy resin, which is most likely
condensible.

Jim

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