Re: 10w30 vs 25w40 in a 1986 3.0 mercruser?
Your 3.0 motor did not use 10W-30 oil back then. Mercruiser in their owners manual and service manuals always recommended 30 or 40 grade oil, depending on temperature. They even stated not to use multi-grade oils in their manuals. It was quite a few years later that Merc came out with their 25W-40 oil for stern drives. You can use either the straight grade oil or the newer Merc oil in your motor.<br /><br />Someone replaced your oil cap with an automotive one that happened to fit. From the factory, the Mercruiser oil cap was solid black.<br /><br />---------------------------------------------<br /><br />Edited from the Mercury website is the latest oil requirements for Mercruisers:<br /><br />IMPORTANT: The use of non-detergent oils, multi-viscosity oils (other than Quicksilver 25W-40), synthetic oils, low quality oils or oils that contain solid additives are specifically NOT recommended. <br /><br />The table below is a guide to crankcase oil selection. The oil filter should always be changed with the engine oil. <br /><br /><br /> <br />All Temperatures<br /> Mercury Precision 4-Cycle 25W-40 Marine Engine Oil <br /> <br />Below 32 F <br /> SAE 20W<br /> <br />32-50 F <br /> SAE 30W<br /> <br />Above 50 F <br /> SAE 40W<br /> <br /><br />This crankcase oil recommendation supersedes all previously printed crankcase oil recommendations for MerCruiser gasoline engines. The reason for this change is to include the newer engine oils that are now available in the recommendation. <br /><br />Older owner manuals, service manuals and other publications that are not regularly updated will not be revised to show this latest engine oil recommendation. Current owners manuals, service manuals and other service publications that receive regular updates will receive this revised recommendation the next time they are updated.
