CHAPTER 4 Bleed screw


= Possible bleed points Injectors


Injector pump


Stopcock Lift pump


Primary filter


Engine fuel filter


Fuel problems


When a diesel slows down and stops in service, first make sure that the propeller has not fouled. If the prop is clear and the engine has not overheated, it almost certainly has a fuel problem. This must be tackled systematically. • Make sure there is fuel in the tank and that the cock is turned on.


• If fuel is in good supply, it is likely that either water has entered the fuel or a filter is blocked. Start at the primary filter.


• Depending on the type of filter, there may be a sight glass to check for water and a tap to drain any off. Deal with this first. Next, close the tank fuel cock, open the filter and remove the element. Clean it in fresh diesel, or – more likely – replace it if it is a throwaway cartridge type. It is imperative that spares are carried at all times.


• Re-assemble the filter, re-open the tank cock and, if the tank is above the filter, allow it to fill by gravity. In order for this to happen, you must open the bleed screw on the top to allow air to be displaced. The bleed point may be a hexagonal bolt head requiring a spanner, and it should not be necessary to open it more than a turn or two. It is critical that no air is present in diesel fuel,


so wait until the fuel is running clear out of the top (no air bubbles left) before closing the bleed screw.


• Because air may well have been dragged in further up the line when fuel stopped flowing, the engine filter should next be bled. In extreme cases it may also be necessary to change this element as well and at least one spare should be in the boat’s kit. Bleeding requires the fuel lift pump to be operated manually to supply the necessary pressure. Find the pump on the engine block by following the fuel pipe from the primary filter towards the engine filter. Next, feel for a small lever which is operated by moving it up and down. Fuel will now flow to the engine filter, which is bled like its predecessor.


• Many engines will now start without further bleeding, but some may require the injector pump also to be bled. In this case, look for a bleed screw on its body, perhaps on the side or top and bleed it using the lift pump as before. If it still won’t run, try bleeding the injectors themselves by carefully ‘cracking’ the union nuts of the fuel pipes.


• Give the engine a prolonged crank and it should now start. If not, check for air as described and try again.


MANUAL OF SEAMANSHIP | 33


Power units


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