At my boat shop, it is not unusual that someone brings in a boat motor that has been ravaged by low quality oil. In many cases, the oil has started to leave a residue all over the different pieces of the boat making it so that it doesn’t run as well as it should. Residue can cause a great deal of damage to the engine and sometimes result in blockages.
I hate to see the way that these boats are damaged, so I try to make sure that everyone knows that they should be avoiding cheap oil. I show them damaged parts from old motors and advise them to buy specific brands of outboard motor oil to keep this sort of thing from ever happening to their boat motor. I do what I can to make sure that their boat motor doesn’t end up looking the same.