I am sure that their have been past discussion on this topic but here go's anyway.
I am looking for a good marine grade oil for my boat's power plant's, the owners manual advises SAE 40 but I like my synthetics and run Amsoil in my Ford 7.3 L. After lengthy reading I am not sure what is best as synthetics in an older motor can have blow-by dependent on wear, and base oils lack the superior lubricating qualities offered by synthetics. Do marine oils contain added rust inhibitors over conventional automotive oils? I question the previous owners maintenance as they could not tell me what oil they used in these motors, and two year old marine batteries had no electrolytes. I am a little intense on the service of my equipment and a hands on type that most likely stayed with me since the Marines. Any guidance is appreciated, looking for a good reasonably priced oil options for these motors. Thanks All