Quarrendon: Petrol in a Diesel Car? How Worried to Be
Far less than you likely are, provided it hasn't been started. "Have I wrecked it?" is the first thing anyone in Quarrendon asks, and the honest answer is normally no, because petrol left in a diesel tank hurts nothing until it is dragged through the system — by ignition priming, by your starter, or by driving. Petrol in Diesel is who to ring, with the engine left off, and so it stays that way. Further down, this page sets out what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you again.
What petrol in a diesel does to the motor
Passing through a motor, diesel is doing two things at the same time. Before it burns, it lubricates — and then it burns. What keeps the surfaces inside the high-pressure pump and your injectors from wearing down against each other is your diesel flowing through them — they are made to very fine gaps.
The second job petrol doesn't do at all, and the first it does badly. It is thinner than diesel and strips away the lubrication the fuel system rests on, and so a pump running on a petrol mix is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That's where the clattering comes from.
The shape of the issue is clear once you put those together. Contact doesn't do the harm — movement does. Petrol in the tank is a fuel fault. Whatever a worn pump sheds goes on, borne by the fuel, into the fuel injectors further along, which is why a pump that has worked on the petrol is where a mechanical fault starts.
How bad is petrol in a diesel? Four scenarios our technicians see in Quarrendon
Fuelled up, not once started. The best case there is. On a forecourt, and really only there, that petrol is still confined to the tank — since everywhere else your car was driven to get to it. The task is emptying and purging on the spot.
Your ignition turned on, or a short start. Once primed, your system has pulled petrol out of that tank as far as your filter and your lines. Still normally simple: drain, flush, and the fuel filter sorted.
Driven a few miles. Now the pump has spent those miles working on thinned fuel. The work is that tank, your lines, the filter and clean fuel through the whole circuit, and how hard your car was driven matters as much as how far. Driving the kids to Thomas Hickman School is one kind of trip. A run as far as Milton Keynes, under 25 miles away, is a very different task. So is any distance on the M40, under 15 miles from Quarrendon, where the motor has been working hard throughout.
Driven till it protested. Clattering, a ragged idle, smoke, a throttle that has gone soft. The fuel isn't acting like diesel any more, and your motor is saying so. Whether it's the verge on Lay Road, a lay-by or a side road, stop there and leave it. A car stopped soon very seldom has long-term damage, since the fuel drain and the flush, which still come first, deal with it.
Stories Quarrendon motorists hear about petrol in a diesel
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Topping up takes out nothing; it gives you a bigger tank of the same mix. The idea behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
"Current diesels can handle a little petrol" — a myth, and nearer the reverse. A newer diesel runs its fuel through smaller components at higher pressure, which makes the lubrication count more, not less.
"It starts, it drives, and so no harm done" — the myth that catches most people than any other. Diesel in a petrol motor normally means a motor that will not run: the motorist stops, and so does the damage. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually will; meanwhile your pump grinds. Running isn't the same as fine.
Myth: a two-stroke additive lets you to drive home. It is an old workaround, meant for another fault. What petrol has thinned remains diluted, and that petrol remains in your tank regardless.
The next start draws petrol back round your pump from the fuel lines and the filter, where some of that sits after your engine has run. That is why a DIY tank drain doesn't leave you sorted — a myth. It is also really dangerous to drain petrol into a can by the roadside.
Petrol in a diesel: how does it occur?
It's rarely carelessness, and no one does it on purpose. One way only, since of the nozzles: the slimmer petrol one slides inside a diesel filler with almost no resistance, while the diesel one mostly will not fit a petrol motor. That is how the forecourt makes it straightforward.
It happens when routine and the vehicle stop matching. A new motor, a hire car or a courtesy car. A household with one petrol and one diesel on the driveway. Your normal forecourt, its pumps suddenly in a different order. A hurried fill on the way to Aylesbury with a train to catch. A new-to-you diesel Renault Megane, its first fuelling, and a driver accustomed to petrol: exactly when it happens. Add a back seat full of kids, a phone call or rain, and habit wins.
How to avoid petrol in a diesel on your next fill-up around Quarrendon
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most usually do. Check the pump's label; the colour is only a clue.
- Plenty of vehicles state the fuel inside the filler flap or on the cap, so check it on the first fill in a vehicle you don't know.
- One of each in the household? Mark your key to the diesel — a coloured fob, a sticker — because intending to remember isn't enough.
- "Diesel", aloud, before you lift the nozzle — every time a new or hired car needs its first tank. It sounds silly. It does the trick.
- Mistakes like this are straightforward to make while your mind is on something else, and so the phone goes away.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler built to block a petrol nozzle, and add-on devices exist for vehicles without one. They are a backstop, not a reason to stop checking the petrol pump.
- Less petrol means a weaker mixture, so stop the moment you notice — though remembering that the next step is unchanged. It is still not to crank it.
Put petrol in a diesel in Quarrendon already?
Short and simple, then, is the order of things. Don't fire it up, and don't turn your ignition on. Yet at the forecourt, at Applegreen or anywhere else? Ask the attendants to help you push the car away from the petrol pump. Next, 0333 366 0103. We will ask what got in, about how much, and if it's been run.
If it was AdBlue rather than petrol, say so. That's a different problem — corrosion and deposits and not lost lubrication — and it has its own page for Quarrendon.
What makes one Quarrendon petrol in a diesel task cost more than the next
A fair single price does not exist here: four situations, four separate tasks. Which of them you are in is chiefly what shifts your cost. Where the vehicle is matters too, and whether a van can safely get to it, after the share of petrol to what the tank holds.
Before any quote, not after, we ask three questions: the fuel that got in, the quantity, and if it's run. That is why. Those answers change a range into a straight figure.
About Quarrendon itself
Quarrendon is a suburban area in Buckinghamshire, situated near the River Great Ouse and characterised by semi-detached housing. Quarrendon sits at an elevation of 78 metres, with nearby neighbourhoods including Haydon Hill, Elmhurst, and Watermead. Quarrendon is located approximately 15 miles from Milton Keynes and 37 miles from London, making it a commuter base for those working in the larger cities. Quarrendon has a population of around 5411 residents.
Quarrendon and Buckinghamshire: where our fuel drain cover runs
Petrol in diesel call-outs around Quarrendon — part of the HP postcode area — go to vans that likewise cover the places round it, Haydon Hill, Elmhurst and Watermead included. A forecourt, a supermarket car park, a lay-by or your own drive are all locations our technicians drain, and the vehicle doesn't need to come to us.
In Quarrendon and still at the pump?
Then you are in the best position there can be. Ring, and keep it turned off.