RACQ Motoring

Diesel Mis-fuelling Device

Diesel Misfuelling Device

Over the past few years diesel engines have become much quieter, more refined and common. Increasingly they are being offered as an option in passenger cars as well as light commercials and SUVs. However with this added refinement and popularity it can be difficult to tell what sort of engine is under the bonnet of even common cars - and therefore what type of fuel they need.

We know this because our Road Service patrols and those of other motoring clubs are increasingly being called to cases of mis-fuelling.


If you’ve recently moved from a petrol vehicle to a diesel, are in and out of different vehicles or have a fleet using a mixture of fuel types, you may be at risk of accidentally filling your diesel vehicle with petrol.

It only takes a moment's lapse in concentration to put the wrong fuel in, but the consequences can be catastrophic and the repair costs staggering. See our Fact Sheet on mis-fuelling for more information.

How does it happen?

In many cases mis-fuelling is the result of habit or a moment of inattention. The majority of diesel vehicles only have a ‘Diesel’ label on the filler, which offers limited, if any, protection. However the design of service station filler nozzles actually compounds the problem. Unleaded petrol nozzles are smaller than diesel nozzles and will easily fit into the filler neck of a diesel vehicle, making it very easy to introduce the wrong fuel.

A few, generally more expensive models, have an anti mis-fuelling feature built into their fuel filler neck to stop the wrong filler nozzle being inserted, but at the moment these are the exception rather than the rule.

What can be done to help prevent Diesel Misfuelling?

  • If your diesel vehicle doesn’t have a built in mis-fuelling device it may be possible to fit one. RACQ now offers a range of Diesel Misfuelling Devices for popular models through selected RACQ branches and the RACQ Online Shop.

The diesel mis-fuelling device replaces the conventional filler cap and incorporates a locking flap which only allows the correct sized (low flow) diesel nozzle to be inserted. If an attempt to insert a petrol nozzle is made the flap won’t open and no fuel can be introduced.

To determine if there is a misfuelling device for your particular vehicle, refer to the document Diesel Misfuelling Devices suitable for fitment to Diesel Vehicles (PDF, 227KB). The device comes with fitting instructions and can be easily installed by the vehicle owner. No tools are required.

Note: If you need to fill from a high flow pump it will be necessary to remove the device from the filler neck, however this is likely to be a fairly infrequent necessity for most motorists.

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The information provided in this fact sheet is intended as a general guide only. You should carry out further research and investigations into the topics outlined above prior to implementing any actions or recommendations