Hi All:<br /><br />I've got a 2.5 HP Johnson manufactured from 1946-1949 and on it is a decal that says:<br /><br />"Mix thoroughly in a clean can 1/2 pint Mobiloil AF or Mobil Oil SAE Marine oil #4 or a high grade SAE No. 40 oil with each gallon of gasoline"<br /><br />So what oil should I use? Straight conventional 40 weight? 2 cycle chainsaw oil? 2 cycle outboard oil? What about a semi-synthetic?<br /><br />Should I keep the same mix ratio or change it due to the engine's age.<br /><br />I just joined this board yesterday and I'm impressed with the knowledge and interest people have about these old motors.<br /><br />Thanks for your help.<br /><br />John
<br /><br />In 1964 OMC changed the mix recommendations on all pre-1964 engines to a 24:1 mix, using TC-W rated Outboard oil(Two Cycle-Water cooled).<br /><br />The current (improved) equivalent is TC-W3.<br /><br />That would be one oz. TC-W3 rated oil to one gallon of 87 octane unleaded gas.<br /><br />Most stores that sell TC-W3 also sell a mix measuring bottle that can be used to measure out the correct amount of oil for the mix, and for the amount of fuel you are mixing.<br /><br />Great little popper you have. I have the Sea King version of the same engine.