I must confess, I am slightly bewildered by the range of oils that one can use with steam engines. I know that there is a special kind of oil for using to lubricate inside the cylinders, made partly with tallow, because ordinary oil does not work in the presence of water or water vapour. However, should this oil be used only for lubricating inside cylinders, and a lighter, purely mineral oil, used for, for example, the crankshafts, or should the "steam oil" be used throughout a steam engine?
Secondly, there are different ratings of steam oil: what do these ratings mean, and how would I know which rating to use for any given engine?
Thirdly, Stuart seem to sell something called "preservative oil": what is that, and when should it be used?
There are several grades of steam oil, as there are for most oils. SAE 460/600/etc are ideal for non-superheated engines, those using lower pressures, and / or lighter duties.
The higher viscosity, SAE 1000 + is generally considered best for higher pressures, (which = higher temperatures) and greater superheat (again = higher temperatures).
With the smaller stationary engines, a light oil will suffice. Given that most engines run with a light or no load, and many are only run occasionally, a small can will last for a l-o-n-g time!
In an emergency, vegetable oil will stop things seizing up. The tallow base was used, but today oils are more sophisticated. Got lots of strange sounding chemicals in 'em!
Whilst Stuarts and many of the model engineering suppliers sell oil in small quantitites, if you can get together with some friends, or your local club, and buy a quantity, it will be much cheaper. (Hallett oils are one supplier I have used.)
I believe the 460, 600, and 1000 numbers are actually the ISO rating of the oils and not the SAE rating which makes it a bit confusing. The 460 is actually SAE 140 and the 1000 is SAE 250.
I've noticed that a lot of the 2½" gauge fraternity use steam oil for lubricating all of the motion, probably because these little engines tend to run very hot so the thicker steam oil tends to stick better instead of being thrown off.
G'day James. I recall my late father having a preservative oil for his competition rifles. It had a smell not unlike that of the waxy grease that tools sometimes come in. It may be the same stuff. I also recall a grease that was used on 12"/ft engines bright components when they were laid up for a while, same colour and smell as the tool grease. The most recent time I saw it was last August when I visited the North Borneo Railway in Sabah, Malaysia. Operations there have been suspended for 12 months while the track is upgraded. Their sole operating 2-6-2 had its side rods coated in the grease.
When I spoke to the representative from the Stuart stand on Saturday at the Midlands ME Exhibition, he said that preservative oil should be applied to all exposed cast iron parts (apart from the outer surface of a flywheel, if used to drive a belt) of an engine to prevent rust.