Boat motor

[Justin9j]

I value everyones opinion  on here. So i hope it is ok if i ask a boat question. I have only had a boat for  9 months now and have a question about lower unit oil. 
Synthetic oil or not.  Motor is a 90 70hp johnson.  I know syn is not what it calls for but I have heard syn will get you more rpms. 

And what brand do Most of you guys run. 

Thanks Justin 

[pjmcla]

Typically Synthetic oils are more stable, more "Slick", and offer better lubrication performance.  I am not an expert in lower unit lubricants.  I would ask a qualified / certified outboard mechanic about your particular engine.  I do know the new 100% synthetic oils that are approved for my engine type provide smoother performance in my aged 2 stroke Yamaha.  I also never run anything except 100% gasoline in the engine.  Never any alcohol blends; ever.   This is after an engine rebuild quite a few years ago when the master mechanic said to me "If you value this engine, run only 100% gasoline and top grade oils".  Based on what I paid him for his expertise on the rebuild, I have taken his advice.   

[BassDetective]

I would stick with the manufacturer recommendations or for an older motor an experienced technician.  I have an older 85 HP Johnson and I went with the standard stuff.  More RPM's isn't always good.  For good boat performance the prop, motor, and lower unit must by in sync or you could have problems.

[pjmcla]

Agreed.  An engine is designed to run within certain parameters.  Over rpm's or over propping are really tough on an engine, especially an older one.  I have no idea how long it has been since I ran my Yamaha at or above 4,500 rpm (engine orange line of 5,300 ).  Usually run 3,500 - 3,750.  Note in my earlier post I said smoother, not faster.   The engine has the Yamaha factory prop of the correct pitch for my "full load" boat weight.   Faster can become expensive very quickly.   

[Justin9j]

I was not really looking for more rpms.  Just thought if it helped the motor work less it would be a good thing.  I tournament fish some but with a 70 hp I'm not out running anything but a paddle boat.  So I don't get in to big of a hurry anyway. We own a auto repair shop here.  But boats are a different animal. I'm still learning.  I just don't want to learn the hard way.

Thanks guys.

[pjmcla]

The main thing is 100% gas and the best 2 stroke oil that is approved for your engine at the correct add rates.  A good quality gas treatment / stabilizer is a good idea as well.  Sta-bil ( blue ) and sea foam are the two most mentioned in the forums.  I use Sta-bil blue; with yamaha ring free every 4 to 5 tanks.   

[Jason]

x2 2 on everything above. Stay away from ethenaol.

Just as an FYI - the one time I got fancy with a motor and tried to get a little more out of it I blew it up!  I'm sure it was more about how I was using it, but who knows for sure.

Jason

[Justin9j]

thanks everyone.  for the help.