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Outboard Motor Mileage

Approximate Fuel Consumption of an Outboard Motor

A number of factors influence outboard motor mileage; things like hull shape, weight and sea state. Generally speaking at Wide-Open Throttle, a gas outboard motor burns about 10-percent of its rated horsepower. So naturally it follows, a 100-horsepower outboard motor would burn about 10-gallons per hour at Wide-Open Throttle. And common sense tell us that at a lower rpm, less horsepower is generated, and therefore less fuel is consumed.

Truth be told, many factors affect fuel consumption. Therefore, inn order to determine your individual engine's fuel consumption one must perform a fuel consumption test. To do so is ridiculously easy. Simply fill a portable fuel tank with a single, measured gallon of fuel. Then run your outboard at wide open throttle until the tank runs dry. The time it takes to burn the entire gallon of fuel tells fuel consumption in time, speed and distance. Next, test speeds from idle to wide open throttle and record the results.
Horsepower RPM Gallons burned per Hour Liters burned per Hour
2 (4-str) 5,000 0.24 0.9
2.5 (2-str) 4,500 0.4 1.4
3.5 (2-str) 4,750 0.5 1.7
3.5 (4-str) 5,500 0.4 1.4
4 (4-str) 5,000 0.4 1.5
5 (2-str) 5,000 0.7 2.5
5 (4-str) 5,000 0.5 1.7
6 (4-str) 5,500 0.5 2.0
8 (2-str) 5,000 1.1 4.3
8 (4-str) 5,500 0.85 3.2
9.8 (2-str) 5,500 1.3 4.9
9.8 (4-str) 5,500 1.0 3.8
9.9 (2-str) 4,900 1.5 5.5
9.9 (4-str) 5,000 1.1 4.0
15 (2-str) 5,500 1.9 7.3
15 4-str) 5,500 1.5 5.5
18 (2-str) 5,500 2.2 8.5
18 (4-str) 5,500 1.5 5.7
25 (2-str) 5,500 3.3 12.5
25 (4-str) 5,500 2.3 8.7
30 (2-str) 5,500 3.4 13.0
30 (4-str) 5,500 2.6 9.8
40 (2 -cyl) 5,500 4.5 17.0
40 (3 -cyl) 5,350 4.5 17.0
40 (di) 5,500 4.0 15.2
50 (3 cyl) 5,500 5.2 21.0
50 (DI) 5,500 5.0 19.0
60 (2-str) 5,250 6.3 24.
70 (2 -cyl) 5,250 7.7 29.0
70 (3 -cyl) 5,500 7.4 28.0
70 di 5,500 6.4 24.2
90 (2-str) 5,250 9.5 36.0
90 (di) 5,500 8.5 32.0
115 (2-str) 5,450 13.2 50.0
115 (di) 5,500 12.0 45.5
140 (2-stroke) 5,450 15.3 58.0

 

di = direct injected two-stroke.

2-str = conventional two=stroke