Re: 1990 mariner 115hp.. choice of oil??
Any two stoke oil rated TCW-3 should be fine.
However, once you decide on a brand, STAY WITH IT. Not all oils are created equal, each manufacturer has their own specific formula of additives to the oil to make it perform and pass the rigid guideline for certification as TCW-3. These additives do not always play well together. Mixing oils of different brands may cause an amount of thickening of some of the oil which could possibly restrict oil flow enough to damage your motor.
Even Pennzoil synthetic is a fine oil.
Direct injected EFI motors can be a bit more 'picky' about their oil, some must have the factory specified oil.
