original patents specify "heavy mineral oil."
On LETPRESS 2002-03-16 Jack Sheedy said he'd heard that automatic transmission fluid would work, but hadn't tried it.
On LETPRESS 2006-06-15, Jim Daggs noted (a) that he knew of a machinist who used Star Parts "Slic" ("which is basically pure silicone liquid") for pulling 1 and 2 point leads. and (b) that he supposed that red automatic transmission fluid might work.
On LETPRESS 2006-06-15 Jack Sheedy also reported that he'd heard that ATF fluid could be used.
(1) ATF Fluid is typically around ISO VG 32 (from a quick online search, correlating cSt to ISO VG). This is also about the same as Mobil DTE 24, which is a light hydraulic fluid. This is clearly much lighter than a sample of known Elrod mold oil.
(2) ATF Fluid can contain EP (Extreme Pressure) additives. These can react with water to form compounds corrosive to bronze bearings. I don't think there's any water in the Elrod mold oil path (through molten metal!) and I don't think that there are any bronze components. Still, why add something that isn't needed? (Unless of course it helps?)
Misc. notes: Mobil Vactra (what I use as way oil on my lathe) should not be used in circulating systems where temperatures exceed 66 Celsius. ("Mobil Vactra Oil Numbered Series" www.mobil.com Canada.)
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