Cars breaking down due to “diesel waxing” made an unwelcome reappearance during last week’s cold weather, according to the RAC.

Analysis of breakdown data on Friday March 2 showed RAC patrols attended almost 500 diesel vehicles of varying makes and ages that had experienced problems with their fuel filters becoming clogged. This represented 5% of the 9,600 breakdowns the RAC dealt with on a day that saw 44% more call-outs than usual for the time of year.

Filters appeared to have become blocked due to the formation of a gel-like substance in the diesel which leads to the engine being starved of fuel and either not starting or losing power. The amber engine malfunction indicator light might also show.

RAC fuel spokesman Simon Williams said: “The RAC last saw issues with diesel ‘waxing’, as it is known, predominantly in the east of the UK in the very cold weather of late 2013, and to a lesser extent in periods of really cold weather since then.

“This should not occur as all diesel produced for UK winter use is formulated with additives to prevent waxing. In addition, modern diesel vehicles are fitted with heating elements on the fuel delivery lines to prevent waxing occurring. We are, however, aware that some vehicles’ fuel lines are more exposed than others which can exacerbate waxing issues.

“The problems seen in late 2013 led to a working group being set up to investigate the cause. The RAC is an active participant along with other breakdown service providers, motor manufacturers and representatives from the fuel industry.

“Frustratingly for motorists, however, there is still no solution to this problem. The most likely explanation appears to be that there are a combination of factors at play involving the diesel itself, its bio content, and the way vehicles move the fuel around their systems.”

He advised drivers of diesel vehicles to ensure their fuel filters were changed in line with manufacturer guidelines, and to keeping their car in a garage if they can, but admitted: “Even then, this may not stop a problem happening out on the road.

“As a member of the working group set up across the industry to get to the bottom of this issue, the RAC is working hard to amass and analyse its breakdown data to help find a solution.”