How misfuelling happens
Most misfuelling calls come from three situations, a hire or courtesy car with an unfamiliar filler cap, a change of habit after swapping between a diesel and petrol vehicle, or distraction at a busy forecourt. Diesel nozzles are wider than petrol nozzles and are designed to make it harder to put diesel in a petrol car, but petrol can still be put into a diesel tank easily since the nozzle fits. Either way, the tank needs draining before the engine runs on the contaminated fuel.
Family vehicles used interchangeably by different drivers, or fleet pool cars that change hands regularly, see this mistake more often than a single-driver vehicle, simply because the driver isn't always thinking about which fuel that particular car takes. It can also happen after refuelling from a fuel can kept for a mower or generator that turns out to hold the wrong type.
Electric vehicle drivers occasionally misfuel a petrol or diesel generator or range-extender fitted to some hybrid models, and the same rule applies, do not run the engine once you realise the mistake.
Why the engine must not start
Petrol in a diesel engine strips lubrication from the fuel pump and injectors, which run at very high pressure and rely on diesel's natural lubricity. Diesel in a petrol engine clogs the spark plugs and fuel injectors and will not ignite properly, causing misfires and stalling. In both cases, running the engine circulates the wrong fuel through components that are expensive to replace, so the single most important thing is to turn the ignition off before starting and leave it off.
If you've already turned the key to the first position without starting, that's generally fine since fuel isn't being pumped through the system yet. The risk begins once the engine actually fires and the fuel pump starts circulating the contaminated mixture through the rail and injectors under pressure.
If in doubt about whether the engine actually fired, even briefly, tell the technician when they arrive rather than assume it's fine, since a few seconds of running can be enough to draw fuel into the injectors.
The draining process on site
Our technician connects a drain line to the tank, usually through the fuel filler or a low-point drain plug depending on the vehicle, and pumps out the contaminated fuel into a sealed container. The fuel lines and filter are then flushed to clear any residue that has already reached the pump side of the system.
Once flushed, we refill with a measured amount of the correct fuel, enough to get you on your way, and run the engine on site to confirm it starts cleanly and idles without misfiring before you drive off. The whole process, from arrival to a confirmed clean start, typically takes 30 to 45 minutes depending on tank size and access to the filler or drain plug.
We check the drain plug or access point specific to your model before starting, since some vehicles need a panel or undertray removed first, which the operator will do carefully and refit once the drain is complete.
If the engine has already run
If you started the engine, drove a short distance, or the engine cut out and you tried restarting it, a roadside drain may not be enough. In this case we recover the vehicle to a trusted local garage where the fuel system can be inspected properly, including the injectors and fuel pump, since running contaminated fuel through these parts can cause damage that only shows up under load.
We'll be upfront with you if we think this is the case rather than attempting an on-site drain that won't fully resolve it. Symptoms that point towards this outcome include the engine cutting out repeatedly on restart attempts, a strong smell of unburnt fuel from the exhaust, or visible smoke that wasn't present before the misfuelling.
Waste fuel disposal
The contaminated fuel drained from your tank is treated as hazardous waste and is transferred to licensed waste containers for disposal through registered contractors, in line with environmental waste regulations. It is never tipped or mixed back into a fuel supply.
We can provide a waste transfer note on request, which some fleet operators and businesses need for their own environmental records, particularly where the misfuelled vehicle belongs to a company rather than a private individual.
Keeping the receipt from the forecourt where the misfuelling happened is also useful, as some stations will offer a partial refund or credit once they understand what happened.
Forecourt and fleet situations
If the misfuelling happens at a filling station, we can attend the forecourt directly, working around fuel pumps safely and clearing the bay as quickly as possible so it can be reopened for other customers. Staff at the forecourt will usually ask you to move the vehicle away from the pump if it's safe to push or roll it, and we'll coordinate with them on where best to carry out the drain.
For fleet and hire vehicles we can invoice the fleet operator or hire company directly where agreed in advance, and provide the driver's details and vehicle registration on the paperwork for the fleet's records. This is particularly useful where the driver isn't the one responsible for settling the account.
Where the forecourt has CCTV or the fuel pump has logged the transaction, keeping hold of your receipt is useful for any insurance or fleet claim, and we can note the pump number on our own paperwork if it helps your records.
