It depends on the API specification of the oil. Check the container for this specification. It will normally be in the format API C* or API S* (*being a letter indicating quality) C-indicates the oil is suitable for a Compression ignition engine (diesel) and S indicates compatibility with a Spark ignition engine (Gasoline/LP...).
Hope this helps
ist real oil, from the thickness and weight, it sounds like its for a diesel engine
Yes, you can mix conventional oil with synthetic oil with no problem.
Only the weight of the oil, 20w 40 is thiker than the 15w40, 20w 40 is the best oil for the old cars although 15w40 is very easier cold start ...
15 is thicker oil and for bigger engines.
No, it is far to heavy. Use only SAE 10w30 or SAE 30.
straight 30W, 10-30w and 10-40w are all ok and recommended
Yes, I used it today.
if it si 15w40 engine oil
pertol,water and motor oil
5w-30 grade. 15w40
15W40
depending on what type of mower and who makes the motor it can vary. if it is a standard push mower you can either remove the dip stick/oil fill and dump the oil out there or look at the base of the motor for a plug or under the deck with the blade for a plug. if it is a riding mower there will be a plug at the base of the motor that can be removed to drain it