Eynsham: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less anxious than you probably feel. "Have I ruined it?" is the first question anyone in Eynsham asks, and the honest answer is normally no, since petrol resting in a diesel tank harms nothing till it's drawn through the fuel system — by ignition priming, by your starter, or by being driven. Leave the engine off and ring Petrol in Diesel — that keeps it that way. Further down, this page sets out what petrol actually does inside a diesel, how far it might have got, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to the engine?
On its way through a motor, diesel does two tasks. Before it combusts, it protects — and then it burns. What keeps the surfaces inside the high-pressure fuel pump and your injectors from grinding against one another is your diesel flowing through them — they are built to extremely fine tolerances.
Of those two tasks, petrol handles the first badly and the second not at all. A pump working on a petrol mix is wearing itself out, because petrol is runnier than diesel and strips out the lubrication your fuel system relies on. Petrol is also made to resist igniting under compression — the reverse of what a diesel wants from its fuel — and that is where the knocking comes.
Together, those make the shape of the issue clear. The damage is done by movement, not by contact. All a tank with petrol in it amounts to is a fuel issue. Whatever a worn pump sheds goes on, borne by your fuel, into your injectors downstream, which is why a pump that has been working on that petrol is where a mechanical issue starts.
Four scenarios we see in Eynsham: how bad is petrol in a diesel?
Filled but never started — as good as it gets. The petrol is in your tank and just that tank, and the job is a drain and a flush where the vehicle sits. This is the one scenario that can only really happen at a forecourt, as anywhere else the vehicle has been driven to get there.
Ignition on, or started for a moment. Petrol has come out of the tank and reached your filter and the fuel lines, since the system has been primed. Still normally straightforward: drain, flush, and the fuel filter dealt with.
Those few miles driven were your pump working on fuel weakened by petrol throughout. How hard the vehicle was driven matters as much as how far, and this work takes in the tank, the lines, your filter and clean fuel through the whole circuit. On the school run to Eynsham Community Primary School, the miles is small. Very different a second time: a trip to Oxford, under 10 miles away, or some mileage on the M40, under 10 miles from Eynsham, where the motor kept labouring hard.
Clattering, an uneven idle, smoke, a throttle gone soft: driven until it complained. That's your engine telling you its fuel has stopped behaving like diesel. Pull up where you are — on the verge on Mill Street, at the kerb, down a side road — and don't move it. A vehicle pulled over quickly very rarely has long-term damage, because the drain and the flush-through, which still go first, deal with it.
Stories Eynsham people hear about petrol in a diesel
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." Topping up takes out nothing; it gives you a bigger tank of the same mix. The assumption behind the advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Modern diesels can handle a little petrol" — a myth, and closer to the opposite. At higher pressure, through finer components: that's how a newer diesel moves its fuel, and so the protection counts more, not less.
"It starts, it drives, and so there is no harm" — the myth that catches more drivers than any other. Feed diesel to a petrol engine and it usually won't run, so the driver stops — and the damage stops with them. While the pump wears, a diesel fed petrol normally starts, ticks over and drives away as if nothing has happened. Running is not the same as fine.
Myth: "Add some two-stroke oil and drive the car home." It is an old workaround for a different problem. That petrol is still inside the tank after that, and what it has diluted isn't put back.
The next start draws petrol back round your pump from the fuel lines and the fuel filter, where some of it ends up after the motor has run. That's why a DIY tank drain doesn't leave you sorted — a myth. Besides, petrol drained into a can by the road is truly risky.
Why petrol in a diesel happens at all
A careless moment is rarely the cause, and nobody means to do it. The forecourt makes it simple: the petrol nozzle is the smaller of the two, and it slips into a diesel filler with almost no resistance, whilst a diesel nozzle mostly will not go into a petrol motor at all. So the error runs one way.
The moment routine stops matching the car is the moment it happens. A motor that is new to you — a hire car, on loan as a courtesy car, or just bought. Two cars on one drive, one petrol, one diesel. The pumps in a different order on a familiar forecourt. Fuelling up in a rush on the way to Hanborough, with a train to catch. Years of petrol cars behind you, a diesel Volkswagen Passat in front of you at the forecourt for its first tank — that is when. Throw in a back seat full of children, a phone call or rain, and habit wins.
Preventing petrol in a diesel next time you fill up around Eynsham
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most generally do. Read the pump's label; the colour is just a hint.
- The first fill in a strange motor is the time to check the filler flap — inside it, or on the cap, many motors state which fuel they take.
- Good intentions count for less than a sticker or a fob in a vivid colour on your diesel's key when a home has one of each. So mark it.
- Before the nozzle comes off the petrol pump the first time you fuel a hired or new car, say "diesel" aloud. Daft, perhaps, yet it does the trick.
- Tuck your phone away. This is an easy mistake to make while you're thinking about something else.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to reject a petrol nozzle, and add-on devices are available for cars without one. They are a safety net, not a reason to stop reading the petrol pump.
- The moment you notice, stop: less petrol in that tank makes a weaker mix. What to do next does not change, though — still do not fire it up.
Put petrol in a diesel around Eynsham already?
Then the order of things is short. Starting it is out, and so is switching on the ignition. Still on the forecourt, at Esso or anywhere else? Ask the staff to help you push the vehicle away from the petrol pump. Ring 0333 366 0103 next, with three answers — the fuel, the rough quantity, and whether it has run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost lubrication, make it a different issue — Eynsham has a page all for it.
Eynsham petrol in a diesel tasks: why one costs more than another
There is no honest single price for this, since the four scenarios above are four separate tasks. Mostly, your cost moves with which situation you are in. The proportion matters next, meaning how much of your tank is petrol, and then the location of the car and whether reaching it is safe for a technician.
Three queries come first, before quoting, instead of after — what went in, how much, has it run — and this is the reason. With those replies, there is a straight figure instead of a range.
About Eynsham
Eynsham is a village in Oxfordshire, situated on the River Thames, with a mix of semi-detached housing and other residential properties. Eynsham sits at an elevation of around 70 metres, close to the nearby villages of Swinford and Cassington. Eynsham is located near the city of Oxford, approximately 5.4 miles to the west, and is part of the wider South East region. Eynsham has a population of around 1886 people, living in a variety of housing types, predominantly semi-detached homes.
Fuel drain cover in Eynsham and across Oxfordshire
Swinford, Cassington and Farmoor are among the spots near Eynsham that the same teams work, answering petrol in diesel call-outs across Eynsham's OX postcode area. You need not move your car to us. Forecourts, supermarket car parks, lay-bys and your own drive are all locations where we work.
In Eynsham and still at the pump?
Nothing beats it: that is where you are. Switched off it stays; then call.