The weight of oil—its thickness or viscosity—is rated according to a series of numbers printed on top of the can. The cans are marked first with the letters SAE (Society of Automotive Engineers). This is followed by numbers: 10–20, 10–30, 10–40, or just 30.
Oil with two sets of numbers normally is used for high-performance car engines. The first number indicates the oil’s viscosity when cold; the second indicates the oil’s viscosity when hot. If you are operating gardening equipment in subfreezing weather, change the oil instead of using an oil with a wide-spanning temperature range. Your owner’s manual will specify what weight of oil you will need in such cases.
- Medium-Service 30-Weight Oil: Unless the equipment manufacturer specifies otherwise, use the medium-service, all-purpose SAE 30 oil for lawn mowers, rotary tillers, garden tractors, and other equipment requiring engine oil. These typically have four-cycle engines in which the oil is not mixed with the gasoline.
- Two-Cycle Oil is used for engines in which oil and gas are mixed together. It differs from standard oil in that it burns at higher temperatures. This feature makes two-cycle oil more compatible with gasoline.
- Transmission Fluid is a special type of lubricant for the automatic transmission found on some rotary tillers, riding lawn mowers, and garden tractors. The transmission fluid must be kept at a certain level in the machine. Read your owner’s manual to learn where to add the fluid, how to check its level, and when to change it.