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Author Topic:   Johnson 225 Ocean Runner Fuel /OIL Consumption
Lopaka posted 03-22-2004 01:26 AM ET (US)   Profile for Lopaka   Send Email to Lopaka  
I have a 1996 Johnson 225 Ocean Runner on my 1996 BW 22' "Justice". Does anyone have an idea as to what I should be seeing in fuel and oil consumption per hour of operation at 4000/5000 rpm?
macfam posted 03-22-2004 08:49 AM ET (US)     Profile for macfam  Send Email to macfam     
A pretty good estimate for a carbed 2-stroke would be 10% of total horsepower at wide open. 225hp x .10 = 22.5 gal/hr.
About half of that at a "comforable cruise". (3500-4500 rpm)
225hp x .05 = approx. 11-12 gal/hr.

Of course these are estimates. Assuming you have the right prop for your purposes. If you load the boat with 7 people and gear, full tank etc, you'll use a lot more.
If you have a clean bottom, less than 1/2 tank and just 2 people, little wind, etc, you'll get better results.

Over the years, with carbed 2-strokes, these estimates have been pretty darn close. These include 13'SS, 17'Nauset, 20'Revenge, 25'Revenge. Only Whalers.....of course!

macfam posted 03-22-2004 08:58 AM ET (US)     Profile for macfam  Send Email to macfam     
Oh yeah...I forgot oil.
I just figure on 50:1 and be done with it.
Yes, less at lower speeds, maybe 150:1 at troll/idle etc. etc. For every 50 gallons of gal of TCW-3
But I estimate 50:1 for everything, then I know I've got enough in the oil tank.
I always carry an extra gallon of Yarmalube, no matter what.
I've "donated" more than a couple of gallons in my day for those guys that ran out.
Lopaka posted 03-22-2004 01:33 PM ET (US)     Profile for Lopaka  Send Email to Lopaka     
Thanks for the insight. How about the use of 87 octane gas? I've had a recent opinion suggesting that I should only run mid-grade (89) fuel in the 225 Johnson...what do you think? Cost is important.
jimh posted 03-22-2004 01:59 PM ET (US)     Profile for jimh  Send Email to jimh     
A good estimate of fuel consumption by an internal combustion engine is that it will consume 0.5 pounds per hour per horsepower. This works for many types of engines. Modern engines may be more efficient than this. Let's see if that jives with the estimate given above.

At 225-HP, you will burn 113 pounds of gasoline in an hour. That is about 20 gallons per hour. This is fairly close to the estimate given about as 22.5 gallons per hour.

There will be quite a difference between 4000 RPM and 5000 RPM.

It is hard to say how much horsepower you are using at a certain RPM.

Lopaka posted 03-22-2004 02:16 PM ET (US)     Profile for Lopaka  Send Email to Lopaka     
Thanks much...what are you using as the weight of 87/89 octane fuel (113 lbs divided by 7 lbs per gal of weight would be about 16 GPH)but at what RPM?
tully_mars posted 03-22-2004 10:02 PM ET (US)     Profile for tully_mars  Send Email to tully_mars     
My 225 Evinrude Ocean Pro would burn upwards of 28 gph at WOT (floscan) and would cruise at 4200 rpm with 14gph burn. In my 21 Outrage this equated to 24 knots.

Capt. TM

tully_mars posted 03-22-2004 10:04 PM ET (US)     Profile for tully_mars  Send Email to tully_mars     
BTW, my Evinrude was a 1996 model too, so this emperical data may help you.

Capt. TM

jimh posted 03-22-2004 10:32 PM ET (US)     Profile for jimh  Send Email to jimh     
The density of gasoline is given as 0.67 gram/cubic-centimeter

Thus gasoline weighs:

0.67 grams      1000 ml      3.7854 litre    1 kg         1 lb.        6.8 lbs. 
___________ X _________ X _____________ X ___________ X _________ = ___________
1 ml 1 litre 1 gallon 1000 grams 0.373 kg. 1 gallon
jimh posted 03-22-2004 10:57 PM ET (US)     Profile for jimh  Send Email to jimh     
Yes, my math was off in my earlier example. :-(

Weight of Gasoline
This reference give the weight of a gallon of gasoline from 5.8 to 6.5 pounds:

It must vary depending on the temperature and the grade of gasoline.

Let's call it 6 lbs./gallon.

Fuel Consumption Per Hour Per Horsepower

Here are some figures from:

---begin quoted material----

Typical BSFC ranges are as follows. As usual, there will be exceptions, but this should serve as a general guide:

0.26-0.34 Large industrial four-stroke diesel engines (very small hp/weight ratios)

0.28-0.36 Other four-stroke diesel engines

0.32-0.38 Two-stroke diesel engines

0.37-0.44 Fuel injected four-stroke gasoline aircraft engines

0.40-0.48 Fuel injected four-stroke gasoline automobile engines

0.43-0.48 Carburetted four-stroke gasoline aircraft engines

0.48-0.60 Carburetted four-stroke automobile engines

0.55+ Two stroke gasoline engines

0.55-0.70 Four-stroke aircraft engine takeoff fuel flows

Engines don't maintain a fixed BSFC over their entire range. Typically an engine's BSFCs when producing only a fraction of its rated power are quite high. This is due to thermodynamic factors which limit the engine's efficiency when it runs cold. BSFCs typically reach their lowest value for the engine in the 50-80% power range. Then then begin to trend upward again as friction begins to play a dominant role and/or the mixture must be enriched to provide for adequate engine cooling.

------end quoted material----

With these new numbers, let us re-calculate the fuel consumption of a 225-HP 2-stroke gasoline engine in pounds per hour:

225 X 0.55 = 123.75 pounds

If we are using 6-pound/gallon gasoline that will be

20.625 gallons per hour.

Note that the reference above suggests that the lowest value is obtained in the 50-80% range of the engine power. This may explain why "cruise" is the most efficient speed. At WOT the engine would probably burn more fuel per hour than calculated using the 0.55 figure

At 50% throttle we would only be making 113 HP thus burning about

113 X 0.55 = 62.15 pounds or 10.4 gallons per hour

Bigshot posted 03-24-2004 01:09 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ya know many people have been "cited" for posting an answer that they have no real hands on experience with, is this thread excluded? Not to be a buster but 3 pages of math equations is probably not what he was looking for.

I OWN a 225 Ocean Runner and I do burn 23.5gph at WOT. She will consume 11-14gph at cruise(35-4200) and will consume a gallon of oil to every tank of fuel I burn(85gal capacity) which is usually about 8-10 hours per tank. I run 89 or 93 octane and do not run 87 in anything I own. If cost to run it is a deciding own the worst engine being its appetite for fuel. For $.10/gal, run 89 if possible, not gonna kill ya being it is only another $5-8 per fill-up. Run good quality oil as well, not the Sears brand.

I fill mine usually with 5gal jugs and one day my friend said it is sad that it takes longer to fill the tank than it does to burn it.

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