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Diesel waxing – DERV fuel filters blocked with wax; find out why

Posted 19th December 2019

The winter season has hit and numerous calls have been flooding in reporting issues with the latest shipment of diesel fuel.  On-site diesel dispensers are slowing down left, right and centre thanks to a higher percentage of Biodiesel. This diesel is gelling up fuel filters in as little as a day!
The industry has speculated that it is possible the problem is caused by the addition of animal fats or tallow.  These additions to the fuel increase the saturated level above that of vegetable oils. Therefore, the fuel becomes more prone to waxing up or gelling as it begins to crystallise at a higher temperature.

Replacing diesel filters

We’ve been to sites to replace many filters and the fuel pumps spin up again no problem. This leads us to believe the issue is not with the fuel tanks themselves but rather the gas oil and diesel inside.

Most of our clients we’ve seen affected have a high throughput of diesel. Therefore, the diesel isn’t stagnating long enough for the issue to be caused by waterborne diesel bug.  With even fresh deliveries causing issues it further reinforces the idea that there is an issue with the Fatty Acid Methyl Esters (FAME) in the fuel.

Will diesel additives fix it?

Adding kerosene to diesel means the fuel has fewer paraffin waxes which result in poorer fuel economy.  However, due to the lower amount of the waxes it can bring down the overall level of gel and wax build-up occurring in the fuel.  This might also dilute the tallow making the fuel less susceptible to waxing up.  It is generally not recommended due to the high tolerance of common rail injection systems.  The military used this technique in colder climates. 

Ways to prevent diesel waxing?

Modern diesel cars often have heaters that heat the lines and filters to help the car start in cold conditions.  This is something that maybe tank and dispenser manufacturers could work into some of their products, preventing this issue in the future. However, it is rare for the UK climate to require any additional tank heating for diesel.

Why does diesel gelling happen?

Gelling is caused by the waxes in the diesel fuel crystallising when the temperature drops below as high as +4.4ºC.  This is known as the cloud point of the fuel. The diesel becomes cloudy as the waxes join together to form increasingly large clumps of wax.  These clog fuel filters quickly and without a way to raise the temperature, the equipment will be starved of fuel.

Winter diesel mixed with additives after October

Another theory we have is that this latest batch could still be a summer specification of diesel.  From October onwards, fuel companies add a series of additives to help the diesel flow better during the winter months and prevent gelling. If these additives were perhaps missed out or fuel was delivered from an earlier batch, that fuel might not be winter specification diesel.

Diesel testing

We have tested several batches of fuel with our laser particle counter.  The results did not show a significant increase in particle count or size over what we would expect from ISO4406 codes.  This may be due to the cooler temperature during early morning refuelling, typical of a busy yard. When we test the fuel the temperature may have increased enough for the ambient temperature to have gained a few degrees C.

This temperature change may also be why the issue is not affecting vehicle-mounted engine filters.  The increase in temperature of the engine and warm returned fuel may be allowing any waxing to dissolve before becoming a blockage problem.

If we get any further information, we’ll be sure to update this article.


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