Personally I would not use a mineral oil in this unit as this little engine does work hard and the oil may emulsify under the heat. The semi-synthetic sounds the ideal way forward.

Emulsify?

Heat does not "emulsify" oil, and if it did it would still need something to emulsify with.

Oil usually emulsifies with water, when the engine doesn't get hot enough to boil the water off (as in short-tripping), and/or when somethings putting more than the usual amount of water in the oil, such as a coolant leak, excessive blowby, or poor crankcase scavenging.

This is the "mayonnaise" sometimes found under the filler cap, and if the above conditions favour it it'll tend to happen with any oil, since its primarily a physical rather than a chemical reaction.

Heat carbonises and oxidises oil, causing varnish and coke/sludge formation. Mineral oil is generally more vulnerable to this so that's probably what you were thinking of.

Not relevant either way to the OP's fix though.

Edited by edlithgow on 25/09/2016 at 17:42