Monday, August 12, 2019
Broadly speaking, oil for 2-stroke motors are broken down into water-cooled, i.e. marine applications and air cooled.
Marine applications will usually be clearly identified and will have the identifier TC-W3 somewhere on the label. TC stands for "Two-Cycle". The "W" stands for "Water cooled" and the "3" is the latest release of minimum specifications.
Water cooled applications are considered less demanding than air cooled applications because cylinder and head temperatures are almost always lower in water cooled applications. Consequently, oils for marine applications do not need as much oxidization resistance or as much high temp/extreme pressure capability. Marine oils are often less viscous than air cooled applications because viscosity drops with temperature.
Air-cooled applications are messier. According to this source, there are three competing sets of standards: ISO (Euro/Global), JACO (Japanese) and API (American Petroleum Institute).
Roughly speaking, the ISO "GD" standard is the most demanding in terms of requiring the highest levels of high temperature and extreme pressure resistance and clean burning.
ISO "GC" and JACO "FC" are roughly equivalent. Any oil that meets ISO "GD" automatically meets and exceeds those standards. Generally, GD, GC and JACO FC require some amount of synthetic base stock to meet the conflicting requirements of extreme pressure and clean burning.
ISO "GB", JACO "FB" and API "TC" are roughly equivalent and are not very demanding. These standards can be met with mineral oil base-stock and can be very cost effective.
JACO "FA" oils are used in third world countries and are quite dirty (ash and soot) by modern standards.
Layered on top of this complexity are Environmental Protection Agency pressures to reduce the amount of oil in 2-stroke fuel. In order to function, the oil must not combust. That means that some, perhaps most of the oil is released to the environment as aerosol.
The old standard used to be 32:1. That is, one ounce of 2-stroke oil to each quart of gasoline. The current standards are 40:1 and 50:1 with some applications asking for 100:1. At 50:1 oil films are repopluated about half as fast as when engines ran 32:1 and the oil chemistry is stressed that much more.
If you found yourself in a situation where you were forced to use TC-W3 in an air cooled application your best bet would be to mix it rich and to avoid long, hot, high-load service. Fouled plugs are much cheaper to fix than scored cylinders.