Mobile 10W-40 Oil in a 2006 EFI 60hp mercury 4 stroke

[sdrago1]

So it has come time to change the oil in my outboard again and I started thinking. The recommended oil for my outboard is the Quicksilver or Mercury Precision 25W-40 in warmer climates (I live in Louisiana) or 10W-30 for the cold climates. My outboard requires about 3 quarts of oil per change. Quicksilver synthetic blend cost about $9/quart (could not find it sold by the gallon) so that is $27 per oil change. My main grip is wow that is expensive for motor oil and really expensive for a synthetic blend i.e. not a full synthetic. I am a big fan of synthetics run Mobile 1 fully synthetic in all of my automotives for years and have been very pleased. The only full synthetic I could find was Amsoil it would cost about the same or maybe a little more. I have heard very good things about Amsoil both auto and marine just never used it. So I started looking in to Amsoil they make a 10W-40 marine that can be substituted for the 25W-40 which makes sense the Quicksilver range 25W-40 and 10W-30 is covering a range of 10W-40 so I think I am good there.

So looking on the Mercury website I find if Quicksilver or Mercury Precision Lubricants 4-cycle outboard oil is not available, use a premium quality 4-cycle engine oil, certified to meet or exceed any one or a combination of the following American Petroleum Institute (API) Service Classification SH, SG, SF.

So now I go to the Mobile website and look at the 10W-40 fully synthetic oil and it exceeds the API Service Classification above.

Almost forgot to add the main reason for using the different oil. Mobile 1 10W-40 is fully synthetic which I like and $22 dollars for 5 quarts which I really like. That means I would be getting a better oil in my opinion and it would cost about half the price. To me that is hard to beat.

Finally, my question is does anyone else run automotive full synthetic motor oil in their 4 stroke motors or is this a terrible idea? Is there really any difference in a marine oil versus automotive oil?

Thanks