MJM Yachts 29z Outboard - Manual (Page 21)

CHAPTER 5 FUEL SYSTEM
- 21 - 29z
5.1 GENERAL
It is important to understand the fuel system aboard your boat. Diesel fuel is different than
gasoline. In most respects it is safer, however precautions need to be taken to maintain the safety
of your boat. Please study the safety precautions in the NMMA publication “Sportfish, Cruisers,
Yachts – Owner’s Manual.”
Diesel engines need to intake more fuel than they burn, and so they differ from gasoline engines
in that they return excess fuel to the tank.
5.2
FILLING THE TANK
The Deck fill is mounted on the starboard side decks and labeled “DIESEL.” As the tank is filled,
vapor escapes the tank thru the vent. Overflow is prevented by an in-line fuel/air separator that
will not allow fuel to pass. However, caution should be taken while filling. Check the fuel level
gauges and listen for the rise in pitch at the deck fill, as fuel reaches the top. Shut off the nozzle
immediately. Do not attempt to “top off” the tank. Variations in temperature as well as trim angle
could cause overflow or vent-line blockage.
5.3 CHECKING
THE SYSTEM
Your engine needs clean fuel to operate. Be sure to buy diesel fuel from a reputable marina. Also,
check the primary fuel filter regularly. The primary fuel filter has a clear bowl that will allow you to
inspect for water and sediment accumulation. You should be able to see thru the fuel in the bowl
at all times. Cloudy fuel indicates a problem. Also, you should not see bubbles passing through
the filter while running. This would indicate a leak on the suction side of the fuel system.
5.4
FUEL CONSUMPTION
To assist you in estimating fuel usage and range, the following chart was developed from sea
trials on hull #1 with the Volvo D4 260HP Diesel engine, showing fuel consumption and range on
112 gallons of fuel (90% of capacity) at various RPM or speed levels. The actual speed you may
achieve is a function of the weight carried aboard, condition of the bottom (barnacles/slime), prop
design, etc.
Diesel engines are more efficient when run at about 85% of maximum rpm. The maximum rated
rpm of the Volvo D4 engine at propeller load is approximately 3500-3600 rpm.
It’s advisable keep the accompanying 29z FUEL CONSUMPTION LOG of engine hours and
gallons on each fill-up to best predict fuel usage.
It’s rare that the boat is operated constantly at higher speeds. Average recreational fuel
consumption between fill-ups is projected at 2-3 gallons per hour of engine time.
RPM Speed GPH Pitch dba MPG Range
900 5.8 0.6 1 68 9.7 1083
1200 7.4 1 1 71 7.4 829
1500 8.3 2 3 74 4.2 465
1800 10.4 3.5 4 75 3.0 333
2100 14.4 4.6 5 78 3.1 351
2400 19.1 5.7 4 79 3.4 375
2700 23.2 7.3 4 80 3.2 356
3000 26.6 8.9 3 82 3.0 335
3300 30.1 11 3 83 2.7 306
3600 33.4 14 3 86 2.4 267