Lawn mower

I know you have some skills / knowledge as it relates to small engines. My brother in law Jack says he's never changed the oil in a lawnmower. Says those Briggs and Stratton motors will still outlast the deck and other parts of a mower without having to do so. I find that hard to believe. I don't mow dirt or other crap but at the end of the year there's a discernible difference in the look of new oil and old oil.

They'll last several years without an oil change if you
(or him) have a small yard.  I am talking about a
Briggs, not sure how long any other will last but I
expect a long, long time.  Do check it everytime you
use it and top it up if it needs it.

If you're mowing yards for other people and really use
it a lot you should change the oil from time to time,
not necessarily seasonally.

They're not going to last as long as the deck unless he
keeps it outside and it rusts.  It sure will last as long
as the damn new carburetors on the cheap ones.  I'm
not sure on the new larger engines but probably still
outlast the carb.

Times have changed, people don't fix things anymore
and things aren't really built to fix.

The oil gets black because the impurities in it gets
burned.  Oil lasts forever but on a small engine there's
no oil filter so it gets dirty.  I've taken old ones apart
where the oil isn't changed and there's a build up of
tar like stuff on the bottom of the oil  reservoir.  

I'm probably not going to change mine anymore since
I'm sure now the carb won't last over a year here,
probably not over three years with a lawn your size.
When they had the old carbs you could fix I was
pretty religious about it but not anymore.