1999 Johnson 115 Fuel Consumption

[imported_74baja]

Hi,
I have a 1999 Johnson 155 60 degree looper. This engine is fairly new to me, so I don't have that good of an idea of how much fuel it uses. I have a portable 12 gallon tank. Does anyone know about how much gas this engine uses per hour at like 3000 RPM? I don't need an exact, I just wanted to know before I made any long trips.
Thanks,
Jack

 

[ezeke]

Re: 1999 Johnson 115 Fuel Consumption

edit

 

[dajohnson53]

Re: 1999 Johnson 115 Fuel Consumption

I've found what ezeke said to be a good rule of thumb with the three largish outboards I've owned. 10% of HP in GPH at WOT, about 25-30% less at cruising speed.

I do almost all of my boating so far away from home and the landing that fuel issues are super critical. Often, getting stuck would require a major hassle, maybe even overnight. Until you get a handle on it, you really should estimate 10-12 gallons per hour AND bring extra. Hopefully you'll get quite a bit better mileage than that at cruise speed (as opposed to WOT), but the last thing you want to do is run out of gas. I always estimate WOT mileage, PLUS an extra hour or two worth of fuel on log trips as long as I have the room; I never feel bad about having extra when I get home. Plus, having the extra fuel in jerry cans allows me to deal with the possibility of my built in tanks having problems. (I can always dunk the fuel line right into jerry cans if I need to). Also, if you're able to spare fuel to a boater in need, that's a good thing too.

That said, I would burn 6 GPH cruisig in my old 80 hp. My 175 would burn about 12 cruising. My "new" 200 burned 18 GPH at WOT on a recent shakedown run so I'm expecting the same rules of thumb will hold true.

 

[dajohnson53]

Re: 1999 Johnson 115 Fuel Consumption

It is realistic to expect a propeller motor to burn 10% of the rated horsepower in gallons per hour when running at wide open throttle or WOT.

If you throttle back and keep the boat on plane and trimmed well, you may run at 70% or less of that amount of fuel.

FWIW I've found the same thing on my engines with outboard jets. At WOT rpm's the fuel usage is the same as for props (10% rule or close to it) and it drops similarly at cruise rpms. The difference is that you're going quite a bit slower, therefore the MPG is a lot less - OR, you need to push more RPMs just to cruise because the 30% loss of power rule of thumb with outboard jets is indeed true. But the GPH at WOT RPMs and percentages that seems to be about the same.