Service your boat engine

Replacing the filter is recommended at 200 hour intervals. Remember to close the fuel stopcock to prevent fuel from draining from the tank. Diesel can be messy and its best contained. Place a bowl below to catch any escapes or try hanging a plastic bag around the filter.

Checking and replacing the primary filter Clean filters are essential to keep water and particles out of your boats engine. Most marine engines have two filters, the primary filter in the fuel lines between the tank and the engine, and the secondary filter between the fuel lift pump and the injection pump.

You should check regularly throughout the season for collected water. It will be clearly visible and will require occasional draining. To drain the filter bowl, hold a container underneath the open cock. Once any water has passed through you will see a stream of clear fuel.

Replacing the filter is recommended at 200 hour intervals. Remember to close the fuel stopcock to prevent fuel from draining from the tank. Diesel can be messy and its best contained. Place a bowl below to catch any escapes or try hanging a plastic bag around the filter.

Check the seal between the bracket, canister and bowl. They won't need replacing every time but as new filters come with seals you may still want to. To fit the filter, reverse the process. Assemble the base plate, bowl and filter as a single stack before inserting the bolt. A smear of oil on the sealing rings of fuel and oil filters help them to bed in smoothly when tightened.

Filling the primary filter with the lift pump can be tedious. Even if you have a dip pipe fuel system you can sometimes shortcut the process by opening the filter's bleed screw and blowing down the fuel tank breather pipe to lightly pressurise the tank and drive fuel into the filter.

Replacing the secondary filter The secondary filter is usually one of two types - a spin-on filter, similar to car oil filters, or a type similar to the primary filter as described above. To replace a spin-on filter, unscrew the filter with a wrench, place a plastic bag around the filter and unscrew it allowing the fuel to drain into the bag.

Bleeding the system Changing the fuel filters allows air into the pipes. For the engine to run properly this must be bled by driving it out under slight pressure from high points in the fuel system. Some engines are self-bleeding, but most require you to carry out a few simple steps.

Firstly, make sure you have plenty of fuel and that all the valves are open. Try to operate the left pump lever - if it won't move, hand turn the engine half a revolution to move the drive cam, then try again. If your primary filter is below the level of fuel in the tank, and your fuel is drawn directly from your bottom of the tank rather than via a dip pipe, you can fill the primary filter simply by cracking open the bleed screw on the top. You should see the bowl fill with fuel, and once clean, bubble-free fuel starts to starts to flow from around the bleed screw. There may still be air on the downstream side of the filter which will need to be vented using the method described below, but having already filled the primary filter accelerates the bleeding process.

In either case, the next stage is the secondary filter. Open the bleed screw and operate the lift pump. This may take several minutes, especially if you have to fill the primary filter this way. Fuel should start appearing around the bleed screw, once this is free of bubbles you can close the screw.