Looking after fuel is essential for keeping your engine running smoothly.

Diesel fuel is, like most fuels, a hydrocarbon and mainly derives from crude oil.

We generally call the fuel diesel oil or red diesel (duty not paid), but its proper name is marine gas oil.

The fuel grade burned in our engines is normally to ISO 8217 DMA. You might remember recently there was a lot on the news about petrol changing in the UK from E5 to E10.

This refers to the grade of petrol. Just out of interest E10 has 10% renewable ethanol in it, whereas E5 only has 5% renewable ethanol in it.

Looking after fuel: The diesel fuel refining process

Apart from having red dye in it, our marine fuel is very similar to road fuel.

A grade of road fuel is to ISO 8217 DFA, often called white diesel (duty paid); this is used in diesel cars, lorries and buses.

It is a bio diesel, just like the petrol above. Why does this matter?

Well, if DMA and DFA fuels are blended, or if the changes to red diesel duty in the UK for leisure craft demand it, then you could end up with your fuel being DFA grade.

The engine will run just fine on either fuel, but the DFA (biodiesel) can clean out your fuel system because of a higher solvent content, known as organic fatty acids (FAME).

Cleaning out the system sounds good, but the dirt has to go somewhere and it tends to end up in the fuel filters.

The filters will remove the dirt but will need to be changed more often.

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So, this in turn means it’s a very good idea to carry some extra filters.

If you have fuel problems and it’s not blocked filters or hose connections, a leak is the other suspect.

The fuel pipe-work is often made from copper pipe. Over a period of time the copper can work-harden (go brittle).

If it isn’t supported or properly clipped to the vessel, the work-hardened copper is much more likely to crack.

This can lead to a loss of fuel to the bilge or even the pipe failing completely. Fuel in the bilge is never a good idea, because of fire and pollution.

Also if the fuel pipe were to fail completely the engine would stop, and could not be restarted until a repair was carried out and the system bled of air.

A lot of commercial vessels are now using stainless steel pipes.

When an engine is mounted on flexible mounts as most yacht diesel inboards are, flexible fuel pipes should be used.

It is very important that the correct grade of hose is used.

The grades are:

• BS EN 853 Rubber-covered wire-braided reinforced hydraulic type
• BS EN 856 Rubber-covered spiral wire reinforced hydraulic type
• ISO 7840 Fire-resistant flexible oil fuel hose.

Normally there will be text on the hose indicating that it is suitable for fuel.

I have seen all kinds of hose pipe used for fuel lines, it always ends up very hard and un-flexible.

The new edition Diesels Afloat (Fernhurst, £18.99) is available at www. fernhurstbooks.com. It follows the syllabus of the RYA Diesel Engine and MCA Approved Engine Course 1.

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Enjoyed reading How it works: Looking after fuel: diesel, hoses and filters?

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