Part 3 (recommended oil for 2-stroke engine)

So how do some oils claim to be multi-purpose or formulated for water and air-cooled engines?

These oils have usually been formulated to meet the National Marine Manufacturers Association (NMMA) TC-WII(TM) or TCW3(TM) specifications. These specifications require the oils to be tested under rigorous test conditions. An air-cooled engine test is part of these requirements. Therefore, a manufacturer can claim multi-purpose applications. Although these oils have been tested in an air-cooled engine and will lubricate an air-cooled engine, an oil formulated specifically for air-cooled engine use may be the best choice for your engine.

So what oil is recommended for two-stroke engines?

The recommendation is to use an oil meeting American Petroleum Institute (API) Service Classification TC. API TC is a designation for high-performance two-cycle engines (typically 50cc to 500cc), excluding outboard engines. This performance rating is determined by engine tests that evaluate

(1) Anti-scuff characteristics,

(2) Piston ring sticking and engine cleanliness, and

(3) Pre-ignition.

In the TC category, a 50cc and a 350cc Yamaha engine are used to evaluate the oil. Some engines that require the fuel and oil to be premixed may use a 2% (50:1) concentration of oil in the fuel. It is very important that the fuel/oil mix is correct. In other words, don't add too much or too little oil to the fuel. If a little does good, more oil added to the fuel doesn't necessarily do better. Too much oil will lead to excessive deposits and could also cause exhaust smoke and spark plug fouling. Not enough oil can lead to piston skirt and cylinder wall scuffing and eventual engine damage. Gasoline-containing alcohol (ethanol and/or methanol) should not be used unless permitted by the engine manufacturer. Alcohol-containing fuels can absorb water and separate from gasoline. Additionally, the alcohol may not be compatible with some fuel system components, such as plastic and rubber compounds. Some manufacturers also recommend de-carboning the engine after 50 hours of operation. This procedure is designed to remove excessive piston deposits and to check for possible stuck piston rings. Some engines allow up to 0.040 in. of soot and carbon buildup on the piston crown before removal of the carbon is required. Not only does MB recommend an API TC oil for the 277 through the 503 air-cooled engines, but also the 532 and 582 water-cooled engines. These 532 and 582 engines run at internal temperatures similar to the air-cooled engines, as evidenced by their use of the same spark plug.

Switching oil

Special precautions should be taken when switching oils, even between the same brands. Because of the special formulation of air-cooled engine oil, these oils generally are not compatible with water-cooled engine oils. Caution should be exercised to ensure that these products are not mixed. Special precautions should be taken when changing from a product designed primarily for water-cooled engines to an air-cooled product, particularly in oil injection systems where the undiluted oils would be mixed. It is recommended that the oil reservoir and lines be drained when changing to another formulation. In applications where the oil is premixed with the fuel, it is recommended that the fuel tank(s) be drained and fuel filters changed.

What is motor oil?