How To Service Your
Diesel Marine Engine!
Part III

Let's continue our diesel marine engine service even further...

Air Filters

To get a clean proper mix of fuel and air, we need to change the filters to get those substances as pure as possible in the engine.

Apart from its filtering function, it also silences the air intake.

Changing the air filter is pretty straightforward. On some engines you can wash the filter element with water and soap, on others you have to replace the filter.

air filter housing
air filter replacement

On the picture you see how simple this is! Open the air filter housing and change with a new air filter. Job done!

Change it every time an air filter gets damaged or is contaminated with dirt.

Fuel Line

primary fuel filter

Fuel is, of course, one of the vital elements in running a diesel marine engine. 

Filtering fuel is a must, since the fuel injectors are very sensitive for dirty fuel.

Water, dirt and other contaminants can mess up your engine's functioning.

Usually there are 2 fuel filters.

A primary filter which is somewhere between the fuel tank and the engine, and the secondary or engine's fuel filter, which sits on the engine block itself.

Change both filters, primary filter first. Look how contaminated the filters are. If they are really dirty, it's time to get the fuel tank cleaned...

dirt in fuel filter
fuel filter element
open primary fuel filter

Every time you open up the fuel line, air gets ine, which we need to remove again. This we do by opening the bleed screws. Just open it a bit and prime the fuel. When solid fuel spills out without bubbles, you can close the bleed screw.

Priming the fuel happens gravity, if the fuel tank is positioned higher than the filter, or through a manual lever, which you can move up and down.


The v-belts on our diesel marine engine make all the rest go round and round. They make sure that seawater is pumped up, the coolant is pumped around and that electricity is made through the alternator. All vital functions.

The importance of checking or replacing a v-belt is to make sure that the tension of the belt is allright.

Too loose and the v-belt will slip, which causes less pumping and power!

Too much tension will wear the belt out and is a strain for the pulleys.

engine belts
twisting engine belt

The correct tension we measure by twisting the belt between our thumb and index. It should only twist for about a quarter turn.

testing belt tension

You can also push the belt between 2 pulleys. A deflection of 1 cm is good.

Your manual will tell you when to replace them. If you see cracks, oil or signs of wear, replace them anyway.

Electrical System

Because our diesel marine engines are always in a humid salty environment, it's wise to spray some protection on the connections or metals which aren't painted and are likely to rust.

These sprays put a layer on them, so that they are protected against the moist atmosphere and corrosion.

marine protective spray

Continue the service or go back to part II

Return from Diesel Marine Engines part III to Boat Maintenance

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