Fuels

Fuels that look similar aren't interchangeable, and some of the differences are legal rather than technical. This page sets out what each is and where it may be used.

Road diesel

Standard automotive diesel, fully duty-paid, for vehicles used on the public road. Often called white diesel, because it's undyed. It's the only diesel that may lawfully be used to propel a vehicle on a public road, and that's a matter of duty rather than of performance.

Winter specification matters in a maritime climate. Diesel contains waxes that begin to come out of solution as temperature falls, and untreated fuel can block a filter on a cold morning. Seasonal grades are formulated to cope with it.

Gas oil

Chemically close to road diesel but marked with a dye and a chemical marker, and carrying a lower rate of duty. It's restricted to permitted uses, broadly, off-road machinery and certain specified purposes. Using it in a road vehicle is an offence, and the marker is detectable in a tank long after the fuel itself has been used.

The rules on what may lawfully run on rebated fuel were tightened in recent years and now cover fewer sectors than they once did. Anyone unsure whether a particular use still qualifies should check rather than assume, because the position changed for a number of trades at once.

Kerosene

Standard domestic heating oil for oil-fired boilers and ranges. It burns cleaner and lighter than gas oil and is what almost all domestic heating installations are set up for. Burning the wrong oil in a kerosene appliance soots it up and can put it out of commission.

HVO

Hydrotreated vegetable oil: a renewable diesel made by hydrotreating waste and residue oils rather than by esterification. It's a paraffinic fuel, chemically similar to fossil diesel rather than blended with it, and it can be used in many engines and burners without modification, though the equipment manufacturer’s approval is the thing to check, not general opinion.

Its attraction is that it substitutes directly. There's no separate infrastructure, no new tank and no new machine; it's the same delivery into the same tank. Its practical drawbacks are cost and availability rather than performance.

Storage life

Fuel doesn't keep indefinitely. Diesel and gas oil degrade over time, particularly where a tank breathes moist air and water collects at the bottom, which is where microbial growth starts. Tanks that turn over slowly are the ones that give trouble, and the answer is to keep them reasonably full, drain water, and use the fuel rather than store it.

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