My Dad had a friend who skipped town and left a bunch of stuff in a business he owned...stuff which ended up in my dad's garage to avoid the garbage. among the items were 3 quarts of harley's finest 20W50 oil. I know it's unsuitable for my bike...only synthetic in it for me......suppose it would hurt my crappy old lawn mower as long as i don't mix it with straight 30 wt in there now?