what oil do i use with champion 40 mower?

Don't know how Blade Runner can comment on what oil you should use without knowing what make of engine your Champion lawnmower is fitted with.

Generally there are two grades for domestic 4-stroke lawnmower engines- either a multigrade 10-40 (sometimes a 10-30 in certain parts of the world) and the single grade SAE30.

SAE 30 oil is used in most side valve air cooled engines such as Briggs and Stratton. The more modern OHV engines from Honda use a mulitgrade oil.

It's worth noting that you should never use an SAE30 oil in a Honda engine that recommends the use of a multigrade oil. This is because the Honda engine uses a neoprene timing belt which is lubricated by the sump oil and in cold starting the SAE30 is very thick and can actually ride off the timing belt from the timing gear.

pleasant
September 2010

Unless you are a contract gardener using the mower every day, you dont need the best oil, you need the most cost effective.
Use 'bog standard' 10/40 engine oil and change it at the end of every season.
My lawnmower is still running sweet after 43 years

Blade Runner
September 2010