What weight oil for mercruiser 4.3 6 cylinder?

Answer 1

According to the Clymer Mercruiser shop manual for such engines dated 1986-1990,you are supposed to use Quicksilver 4 cycle SAE 40 motor oil. If this is not available, any good quality automotive oil carrying an API designation of SE or SF may be used. Also, Mercury Marine does not recommend the use of multi-viscosity oils. On brand new engines the oil should be changed at 20 hours, and from then on every 100 hours. The manual also states that any disposable filter including automotive, can be used. But it does warn not to use any double guard or extra filtering filters. What I've been reading in the mercruiser forums is that many other boaters are using the long style automotive filters,(providing they will fit),and they perform the oil changes when they are not going to be used for the rest of the year regardless of the amount of hours on the oil change. There is some speculation, that if your oil doesn't get to a certain temperature, moisture in the oil will supposedly turn it slightly acidic, which may or may not damage the inside of the engine while it is being stored. If any one can confirm this, it would be appreciated.