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Yanmar Pleasure Boat Marine Engine Help
Fuel System
GM engine return line
GM engine side view
Fuel - an overview
Basic fuel system schematic
Although the drawing below only has two injectors it is the same for 1 thru 6 cylinder engines with in-line fuel injection pumps.
Engines fitted with rotary fuel injection pumps may not have a separate fuel lift pump (H), with the manual priming lever (G), the manual priming 'lever' is then mounted on top of the fuel filter (J).
A fuel tank can also have a stand pipe for the fuel suction side, as drawn below. The advantage is that water and debris are left on the bottom of the tank. The disadvantages are that the system can be a little more difficult to prime and after a period of time the stand pipe can crack, usually at the point where it is welded into the top of the tank, thus sucking air into to the system. This problem is often difficult to find! Even when the tank has a stand pipe, it should also have a fuel shut off cock.
Installation tips
DO:
DO:...install a tank with a drain (P) that you can access reasonably easily.
DO:...install a tank shutoff valve (D) where you can reach it in a heaving seaway.
DO:...install as large a diameter tank vent as practicable to prevent 'spit back' while refuelling. Commercial operators should fit a vent that is 50% of the diameter of the filler pipe.
DO:...put the return line (M) only into the top of the fuel tank. The fuel aerates as it leaves the injectors and putting it into the top of the tank allows the air to disperse. For engines with a high fuel return flow the fuel becomes heated during operation. Putting the fuel back into the top of the tank also helps cool it again. The maximum temperature of the fuel as it enters the fuel injection pump must not exceed 55oC or the engine will not get full power.
DONT:
DO NOT... Fit the primary fuel filter (E) above the tank / fuel level, it is very difficult to get rid of the air trapped inside. Where possible mount it at or below the level of the fuel lift pump.
DO NOT... Fit the tank filler (B) or vent (C) where water can leak in. (A fuel filler mounted on the deck or in the cockpit sole will leak water into the tank unless it is a type fitted with a serviceable rubber 'o' ring.) A good place for the tank vent on smaller vessels is near the top of the transom.
CAUTION...You have two filler points on the deck, both look very sexy and exactly the same, except for the writing. I will bet money that one day 'someone' will put the wrong product in the wrong hole. This will ruin more than your weekend, whichever way you do it! Install totally different looking fillers for water and fuel, preferably at different levels in the boat.
Examples of Primary fuel filters
When selecting a fuel filter assembly, choose one that will handle double the total engine fuel flow. This gives a reasonable 'time to blockage' if a fuel contamination problem occurs. The total engine fuel flow, on a 3GM30 ( 27hp ) is not much greater than the engine fuel consumption as the return flow is low. On a 6CX-ETE ( 420hp ) the total flow is 846 litres per hour at full power. The return flow is 756 litres per hour give or take a bit. A filter assembly must have the capacity to handle the total flow or the engine may not reach full power. Photo's and descriptions
As the engine fuel filter is reportedly 10 micron, I recommend using 10 or 30 micron primary fuel filters. If the fuel becomes contaminated with 'diesel bug', for example, the bug size is 6 microns. If a 2 micron filter is installed it will block very quickly. If a 10 micron filter is installed the 'bug' can pass through and be burnt in the engine, that is until the slime builds up and blocks the filter anyway.
Click on the photo to enlarge it.
Click on the photo to enlarge it.
