Re: Automotive oil in outboards ?
Besides the lack of additives your outboard needs, automotive 30w separates out from the gas if it isn't shaken once in a while. The price difference isn't worth it.
Tell your brother-in-law that it isn't a matter of "running just fine" right now today or tomorrow.
Fact is, in the old days, sae-30 non-detergent oil was specified--at high mix ratios such as 24:1, or higher. 16:1 was very common. At the same time, a factory approved tune-up included pulling the cylinder head and scraping the carbon out. The piston rings also stuck, requiring an overhaul.
Modern TCW-3 outboard oil has a detergent to prevent that problem. Or at least greatly reduce it. It also contains other additives to reduce wear, corrosion, etc. Synthetic components, if included, provide superior lubrication and reduced smoke and are bio-degradeable.
OK, you may say then just use sae-30 with detergent. Automotive oils contain metallic detergents that leave deposits in the combustion chamber and rings of outboards that are impossible to remove without tearing it down. Remember, unless it is a real clunker, the oil in car engines does not go through the combustion chambers. TCW-3 outboard oil has ASHLESS detergents.
In order to be certified for TCW-3 service an oil must be submitted to NMMA for testing. Note the stuff on the market that does not have the certification and NMMA logo on the label. Their oil either has not been submitted for testing, OR it was submitted and flunked the test.
Will the sae-30 lubricate the motor? Of course it will. If you mix it at 24:1 or higher. Will it cause problems in the long run? Wait and see.
