Last month an Ohio, USA-based driver of a 2022 Jeep Wagoneer (not a cheap car, please note…) discovered that when he tried to start his shiny 4x4 in the morning after refuelling, it refused—like a stubborn donkey.
Sensing that something was seriously wrong, he had the car taken to his local garage, where a technician found that the petrol tank and fuel lines were full. Of diesel. The unfortunate driver had unknowingly given himself a tank full of DERV when he wanted 95-octane petrol. The fault, in this case, was not his own but that of a Circle K fuel station in the city of Avon, Ohio, which had mistakenly filled its underground petrol tank with diesel, and vice versa.
At least 14 customers have been affected, and Circle K is now facing the prospect of paying to repair all of these vehicles.
This is a bit of an outlying case, though. Normally, ‘misfuelling’ occurs when there’s an error between the car and the pump. That’s human error, in case you were wondering. Around 1,000 such incidents occur each year in Ireland, and while it can be an expensive mistake, there are some things you can do to help reduce the cost.
First off, as soon as you realise it has happened, stop. Stop everything. Hopefully, you’ve spotted the error while still on the forecourt, and the most important thing you can do right now is—nothing. Don’t, whatever you do, attempt to start the car. Go into the shop or payment kiosk and alert the staff, explaining what has happened so they know you won’t be moving for a while.
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The petrol station staff should also be able to help. Most will know the number of a local service that specialises in misfuelling issues, or, if you’re a member of the AA or a similar roadside recovery service, they should be your next call.
How much is this all going to cost you? Well, if you haven’t tried to start the engine, then you could be looking at a bill of around €200–€400 for a specialist call-out to drain your fuel tank and flush the fuel lines. Don’t attempt to do this yourself. Fuel vapour is incredibly flammable—explosive, even—in confined spaces, so this needs to be done by a specialist who knows what they’re doing.
Oddly, putting diesel into a petrol car is generally less damaging than the other way around. Again, the critical thing is not to start the engine. However, putting diesel into a petrol engine is theoretically much harder now, as diesel fuel pump nozzles are larger than the aperture of petrol fuel tank filler necks. Equally, trying to run a petrol engine on diesel will mostly cause the spark plugs to clog up, meaning the engine will misfire and eventually cut out, minimising the potential damage. That said, running a petrol engine on diesel can damage the catalytic converters, leading to expensive repairs.
Theoretically, the same nozzle mismatch issue applies to putting petrol into a diesel car. However, when this does happen, the damage—if you turn the engine on—can be catastrophic. According to the AA, “Running a diesel engine, even partly, with petrol can cause a build-up of swarf [tiny metal filings — Ed]. These imperfections can clog filters and damage sealants. The inherent lubrication within diesel fuel is necessary, as a modern diesel engine is much less tolerant. Petrol doesn’t have these properties and will cause undue wear and tear.”
The longer you run the engine on the wrong fuel, the more damage you’ll cause. This can lead to needing a full engine replacement, which can cost many thousands of euros—potentially a five-figure sum (and not a small five-figure sum) if it’s a newer model.
Misfuelling is more likely to occur with older cars, which don’t necessarily have the right fuel filler valves to prevent mistakes. Generally speaking, the newer and more advanced the engine design, the bigger your problems will be if you misfuel. Even diesel engines have had, since the early 2000s, incredibly delicate high-pressure injection systems.
Those ‘common rail’ diesel injectors have microscopic holes at one end, which spray a fine mist of diesel into each cylinder. If those become clogged with metal swarf, you’re facing major and expensive problems.
Equally, don’t believe the old stories that ancient diesel engines—Ford’s old 1990s 2.3-litre unit is a common one in these tales—will run on anything that burns. As noted, diesel fuel acts as its own lubricant, and diesel engines are designed to need that lubrication.
Finally, there’s HVO. Hydro-treated vegetable oil is now entering the Irish fuel market, primarily through Certa and Maxol stations, as well as Go stations in Northern Ireland. It’s a plant-based diesel substitute refined from waste cooking oils and claims to be 90 per cent lower in CO₂ emissions than conventional diesel.
This doesn’t mean it can be put into a petrol engine. HVO is designed specifically as a diesel substitute, so if you put it in your petrol car, the same issues apply.
