I originally thought I would write a response the last time this subject came up, but I decided against it at the time. Now, I've just become too exasperated to not say anything. First, please note that the motivation for this response is not any one individual, but rather a composite of several years of stories and questions heard around these parts. If you feel like one of the pseudo-anecdotes may refer to you, well rest assured, it probably doesn't. However, feel free to take heed. :) Also, I apologize for the possibly rambling nature of this message as well as the tone; hopefully you can stick with it, or just read the punch-line at the end.
I am continually amazed by the many folks out there in letpress-land who will spare no expense and amount of time in order to lovingly restore a press back to a "showroom-like" gleam. They'll agonize over what solvent to use when cleaning up and what color the pinstripes should be. However, when the time comes to actually use the thing, they'll run down to wal-mart and buy the nearest thing labelled "oil" on the shelf. I can't tell you how frustrating I find that. That's probably the exact opposite of where the emphasis should be, as it's always possible to repaint a casting, but once the mechanical bearing surface has been damaged in some way, there's no going back. These are, for the most part, machines of a different era that were engineered in different ways and which have their own unique requirements. As I'm sure we're all aware, they're not going to make any more of them, so those that truly want to save them for future generations ought to take the time to do things properly. Luckily, doing the "right thing" is neither difficult or expensive.
I know that a lot of folks just use plain old motor oil, both with and without detergents or additives. The rationale usually goes something like, "well, lubricating a gasoline or diesel engine is clearly a lot tougher job (because of heat, forces, or what have you,) therefore it should be just fine to use when lubricating my 8x12 old style. It's true that a printing press likely does not operate at the same temperature range as an internal combustion engine, however operating temperature is just one of dozens of different aspects of a given lubricating application. In fact it isn't necessarily even the most important aspect. The primary lubricating need of our equipment is a plain bearing running at relatively slow speeds and potentially high loads for often short intervals. Motor oil is designed to be used in a high-temperature, high speed application with pressurized lubrication: oil is constantly being applied at high pressure to the points that require lubrication, and then quickly drains away. Plain bearings require a lubricant that will form a thin film that will remain on the bearing surface for relatively long periods of time. The two applications, really, couldn't be more different.
Lubricant manufacturers produce hundreds, if not thousands, of different types of lubricants. They do this not (for the most part, at least) as a gimmick to get people to buy lots of oil unnecessarily, but because there are many different applications, each with unique needs. It's not hard to find examples of the problems caused by using incorrect lubricants. The first that comes to mind is that which occurred when Mobil changed the formula of some of their Vactra numbered way oils. These oils also happened to be used for high speed web presses (check the archives for references to this) and the reformulation caused numerous equipment failures. Now, it may be true that we don't often get into situations where a catastrophic or spectacular failure occurs, but it certainly shortens the lifetime of the equipment in use. Why risk damage when the correct lubricant is usually not much more expensive than than the stuff you're currently using?
I've spent a fair amount of time researching modern equivalents to the various lubricants recommended by Monotype for their type-casting machines. Some of these applications are very arcane and thus the proper products are rather difficult to come by. However, knowing that the right product helps to assure that the longest and best life can be obtained for our equipment makes that hunt worthwhile. Luckily, printing presses are somewhat simpler machines, so it's less of a problem but no less important to do properly.
The punch line:
The proper oil for the equipment that most of us are using is simply called "machine" or "turbine" oil, usually a medium-heavy (ISO 68) to heavy (ISO 100) weight. I like Mobil Vactra Heavy Medium or Heavy or Shell Turbo/T. Not coincidentally, it's the stuff that Heidelberg and Monotype (both are highly representative applications) recommended for general machine lubrication. It's easy to get and has the correct characteristics to keep our machines running happily for years to come. You can get a gallon of turbine oil from McMaster-Carr for about 15 bucks. You could also possibly use "way" oil, but it's stickier and I'm not completely comfortable with the risk of trapping contaminants in the bearing. Using motor oil or gear oil or whatever may not seem to cause damage, but the bottom line is that it's not the proper stuff to be using, and I see no reason to be willfull about insisting on using it.
Anyhow, I hope this has been informative for someone and that no one has been terribly offended by this rant. As always, please feel free to contact me with any questions or suggestions.