[Putershark]

There is only one “sure” way to remove moisture from the oil (no matter which type) and that is through the application of heat to the oil. That is why it is critical that your engine thermostats work as designed, and that you run the engine both long and hard enough to "boil off" that moisture before engine shut down, this no matter what is in the crankcase…

We have to understand though the end game in certain people telling you one thing or another when it comes to engine care. Some mechanics (I'm being kind here) are sly and realize that don't get paid as much to change your oil as they would installing a new power head AND (worse yet) will get paid even more labor dollars to install that power head AFTER the warranty has expired so keep that in the back of your mind when hearing recommendations for sure.

The Outboard makers though do know what can happen when oils that do not contain the correct additives (automotive use grades) for the intended marine environment can do to your engine. That is why the recent push to produce oils that have such additives by the OEM’s. There can be though a large difference though in thermal breakdown and lubricity properties and (even more important) deposit levels left behind between the two oil types be it either a 2 or 4 stroke engine. Now if you plan on keeping your engine for a long time, (or for the re-sale value if you do not) then the use of Marine Grade Synthetic oils is a logical route...

Oil (shocking as it may sound) does not wear out, but becomes diluted with fuel, dirt, and deposits over time and it is during that time period (between your oil changes) is where you need to "choose" just how much engine wear you are willing to have occur on your engine? Like the old FRAM ads use to say "You can pay a little now or a lot latter" still holds true

25 years ago I worked on huge engines that rarely had oil changes (just additions) then again, how many engines do you run now that have lube oil pre-lube pumps installed (oil pressure to 30 plus PSI before it was even turned over) and purifiers that sent the oil through a centrifuge to sling out all the crud and deposits and clean oil was always sent back into the engine on each lap and that is why, those engine’s lasted for generations… Engine start up with zero oil pressure though is where you get the majority of your engine wear and is very hard to combat on any engine that does not have a pre-lube pump to get all that "motion lotion" flowing before crank starts to spin.

So post engine break in period and after your standard warm up, if you are running the engine long enough to remove the moisture (some period of or near WOT running before shut down) and are changing the oil as recommended, then for me the choice is clear and I will run synthetic. I though have never heard of it being possible for a synthetic oil to be "too slick" for rings too seal (which by the way, is not the rings primary job)... for if it was, then my fuel burn rates should drop by huge amounts (which they don't) from all that lost heat and friction from using such, true?

More information though on this interesting subject and the fairly recent release of “Marine Grade” synthetic 4 stroke oils can be found here http://www.amsoil.com/StoreFront/wcf.aspx for your viewing pleasure.

Enjoy!