I know people who have used 10w30 mobil 1 but they didn't have good gauges so I don't know what base pressure they got. For degassing urethane it would definitely be good enough. Regular motor oils have additives to get the multiweight rating so you would want a straight sae
30, but the synthetics don't need additives for the 10w rating. I would definitely expect the synthetic oil to have fewer volatile components. The standard distilled/refined mineral oil for direct drive pumps usually has a 19 in the name, like the TV019 someone else mentioned, or Inland 19, or Invoil 19, etc. This is advertised as either the same as or one step "better" oil than the duoseal oil used in lower speed belt drive pumps, which works well in either direct drive or belt drive pumps. I'm sure you can find a data sheet somewhere online, to get a viscosity rating, which you can then compare to the motor oil scale to see if 30 weight is really the best. Oh, heck, the Lakers just didled away a lead and went to overtime so hang on a sec - okay, I'm back. From
(another good source of vacuum stuff), they give viscosity specs on inland 19 of 54 cst (251 SUS) at 40 deg C and 8.1 cst (52.7 SUS) at 100 deg C. Normal pump operating temps are in the warm to just too hot to touch range, or 40-70 deg C. I found
which gives viscosities of 9.6-12.9 cst at 99 deg C for SAE 30 and 5.7-9.6 cst at 99 deg C for SAE 20 motor oil, so SAE 30 may be just a tick on the thick side but given it's availability I wouldn't hesitate to try it. I also found a listing for Mobil 1 10W30 as 59 cst at 40 and 10 at 100 deg C, so it's on the thin side of 30 weights and should work okay. Well, the Lakers managed to get the win so I'll stop typing :-).
-- Regards, Carl Ijames carl.ijames at verizon.net