There should be no problem with mixing them.
Yes of course you can mix them what what would be the reason to do so.
A diesel engine would use 15w40 a gas engine could use 15w40 or 10w40
10W40 or 15W40 semi-synthethic
10W40 or 15W40
10W40 is a thinner oil, and would allow the engine to run more freely, and although both are suitable for winter usage, a thinner oil will usually help the engine start more easily in cold weather.
15 is thicker oil and for bigger engines.
not recommended
10w40-15w40
15 is thicker oil and for bigger engines.
No, use only the weight recommended by the manufacture which is 15w40. I suggest you use a Synthetic oil on this air cooled 4 cycle engine.
Yes, you can mix conventional oil with synthetic oil with no problem.
10w40 unless its a recent 1.5 diesel (renault engine) in which case i THINK its 15w40, best getting that checked out though