Mercruiser Fuel Consumption Calculator

Mercruiser Engine Fuel Consumption Guide

Estimate fuel consumption for Mercruiser marine engines to plan your boating trips efficiently.

How It Works

The calculator estimates fuel consumption in gallons per hour (GPH) based on engine horsepower, brake specific fuel consumption (BSFC), engine configuration, RPM, and fuel type. Total fuel needed is calculated using either hours of operation or distance and speed. Fuel efficiency (nautical miles per gallon) is provided when distance and speed are input.

GPH = (HP × BSFC × Engine Factor × RPM Factor) / Fuel Weight

Total Fuel Needed = GPH × Hours (or Distance / Speed)

Fuel Efficiency = Speed / GPH (when distance and speed are provided)

Typical Consumption Rates

Engine Model	Horsepower (HP)	BSFC (lb/hp·hr)	Typical GPH @ RPM
3.0L MPI	135	0.45	4-6 @ 3000 RPM
4.3L MPI	220	0.42	7-9 @ 3500 RPM
5.7L MPI	300	0.40	10-12 @ 4000 RPM
6.2L MPI	350	0.38	12-15 @ 4500 RPM
8.2L MAG	430	0.37	15-20 @ 5000 RPM

Key Factors Affecting Fuel Consumption

• Engine Model: Higher horsepower engines consume more fuel (e.g., 8.2L MAG uses 15-20 GPH at 5000 RPM).
• RPM: Optimal cruising at 65-75% of wide-open throttle (WOT) RPM minimizes fuel use.
• Engine Configuration: Twin engines consume approximately 1.8x the fuel of a single engine.
• Fuel Type: Diesel engines (7.2 lb/gal) are 20-30% more efficient than gasoline (7.0 lb/gal).
• Operating Conditions: Speed, distance, and boat load affect total fuel needs.

Tips for Improving Fuel Efficiency

• Optimal RPM: Cruise at 65-75% of WOT RPM for best efficiency.
• Propeller Selection: Choose the correct propeller to improve efficiency by 10-15%.
• Regular Maintenance: Clean spark plugs, filters, and hull to maintain fuel efficiency.
• Diesel Engines: Consider diesel for 20-30% better fuel economy.
• Plan Routes: Minimize high-speed runs to reduce fuel consumption.

Example Calculation

For a 5.7L MPI engine (300 HP, BSFC 0.40) at 4000 RPM, single engine, gasoline (7.0 lb/gal), operating for 2 hours:

RPM Factor = min(1, 0.6 + (4000/5000)) = 1

GPH = (300 × 0.40 × 1 × 1) / 7.0 = 17.14 gallons/hour

Total Fuel Needed = 17.14 × 2 = 34.28 gallons

If traveling 30 nautical miles at 15 knots: Time = 30 / 15 = 2 hours, Total Fuel = 17.14 × 2 = 34.28 gallons, Fuel Efficiency = 15 / 17.14 = 0.88 nautical miles/gallon

Final Considerations

Accurate fuel consumption estimates help plan efficient boating trips. Always carry extra fuel for safety and account for variables like sea conditions and boat weight.