I have used AMSOIL synthetic oils for a couple of years now and I am a distributor so this may sound like sales hype but I could care less if you buy some from me or not. I just want to say its the best thing I have found so far. I use it in Motorcycles my truck 25000 miles with no oil change and my boat with an old Atomic 25 HP slug which got almost 150 more RPM''s after I put AMSOIL in and ran quiet and cooler by 7 degrees. For Cars the oil change is a standard 3000 miles 7500-12000 on Amsoil so I figure motoring three hundred miles in your boat is like running the Indy so maybe I will change the oil but I ran into hurricanes and had to motor another two hundred now hours I am not sure of allot and the oil is still as slick as a babys butt. Drop me a line if you want to save your motor this is for real lubricant. You must flush your motor first Diesel or Gasoline and some other nifty lube stuff can be had from AMSOIL.
Dealer number #1092248 Jim Jacobs