During cold periods, it is possible for diesel engines to experience starting problems. There can even be issues with engines that are already running. These problems may happen when wax crystals form in the fuel and condensation occurs, this can cause blockages that prevent oil from reaching the engine.

What causes the wax crystals in fuel?

All diesel fuel contains paraffins. The paraffin content gives diesel the high cetane number that makes for efficient combustion.

Normally, the paraffins are dissolved in the fuel. However, when diesel is cooled, these paraffin molecules start to form crystals and solidify. If the temperature is low enough, more and larger crystals can form, which then create a mat on the fuel filter and block it. In severe cases, even the narrow bore pipe work – particularly at bends and unions – may become totally blocked. When this happens, the engine will no longer receive the fuel it needs.

You can tell if paraffins have crystallized in your fuel by their appearance. It might look milky, or there could be a reddish deposit on the bottom of your tank or on the surface of the fuel filter. When the temperature stays low for several days or a spell of extreme weather hits, fuel can experience this crystallization problem.

Using additives to prevent fuel problems in winter

If you’re thinking of using additives in your diesel and gas oil to improve its cold weather performance, there are a few crucial points to bear in mind.

Anti-wax additives

Anti-wax additives are designed to improve the winter performance of fuel. The additives work to prevent the formation of wax crystals and allow effective operation at lower temperatures than the fuel specification.

Can you use additives to improve a fuel’s winter performance?

Blending any additives in fuel you already have must be done when the temperature is higher than the cloud point (the point at which crystals form). The additive must also be fully mixed to create a homogenized blend, and any secondary treatment must be pre-diluted and free-flowing. You should speak to your supplier if you are thinking of using additives because uncontrolled additives can cause problems such as haze and water suspension.
Another important point to note is that existing additives may have already exhausted the sensitivity and response of the fuel, making further additive treatment ineffective.

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