Boreham: Petrol in a Diesel Car? How Worried to Be
Probably less than you are now — as long as nobody has started the car. Till your ignition primes the pump, the starter turns, or the vehicle is driven, petrol in a diesel tank simply rests there and does no harm. Which means the honest reply to the first Boreham query — "have I ruined it?" — usually no. Keep it like that: leave your engine off then call Petrol in Diesel. Further down, this page sets out what petrol really does inside a diesel, how far it may have got, and how to stop it happening to you again.
Inside the motor: what petrol in a diesel really does
Passing through an engine, diesel is doing two things at once. Before it burns, it protects — and then it combusts. Extremely fine tolerances are built into the fuel injectors and the high-pressure fuel pump, and only your diesel flowing through keeps their surfaces from grinding together.
Poorly at the first, not at all at the second: that's petrol. A pump working on a petrol mixture is wearing itself out, since petrol is runnier than diesel and strips out the protection the fuel system depends on. Petrol is also made to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that's where any clattering starts.
Taken together, they make clear what shape the problem has. Not contact but movement is what does the harm. Where the petrol is only inside your tank, it is a problem of fuel, nothing more. Whatever a worn pump sheds travels on, borne by your fuel, into the fuel injectors further along, which is why a pump that has worked on that petrol is where a mechanical fault starts.
How serious is petrol in a diesel? Four scenarios our engineers see in Boreham
Fuelled up, not once started. The best case there is. At a forecourt, and really only there, that petrol is still limited to your tank — because everywhere else your car was driven to reach it. The job is emptying and cleaning on the spot.
Ignition on, or started for a second. The fuel system has been primed, and so petrol has left the tank and got to the filter and the fuel lines. Still generally easy: drain, flush, and the fuel filter dealt with.
A few miles driven, and your pump has spent each of them running on diluted fuel. Mileage is only half of it; how hard it was driven matters equally. Either way the work includes that tank, the fuel lines, your filter and fresh fuel through the whole system. On the school run to Boreham Primary School, the miles is small. A run as far as Chelmsford, under 5 miles away, is a very different job. So is any distance on the M11, under 25 miles from Boreham, where the motor has been labouring hard throughout.
Clattering, a ragged idle, smoke, a throttle gone soft: driven until it complained. The engine is telling you the fuel is no longer behaving like diesel. Leave it wherever it stops: a lay-by, a quiet street, the verge on Main Road. Permanent damage is very uncommon if a vehicle is pulled over soon, and the drain and flush-through that still come first sort it out.
What Boreham motorists get told about petrol in a diesel — and the stories in it
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. A bigger tank of the same mix is all it gives, because topping up takes out nothing. A diesel fuel system doesn't accept petrol by percentage in the way that advice assumes.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the opposite. At higher pressure, through finer components: that's how a current diesel moves its fuel, so the lubrication counts more, not less.
"It starts, it drives, and so no harm done" — the myth that catches more people than any other. Feed diesel to a petrol motor and it usually will not run, and so the driver stops — and the damage stops with them. Feed petrol to a diesel and it usually fires up, ticks over and pulls away as if nothing happened — all while its pump is wearing. Fine and running aren't the same thing.
Not so: a two-stroke additive makes it safe to drive home. It was an old fix, meant for another issue. What petrol has diluted remains weakened, and that petrol stays in the tank anyway.
The next start sends petrol back round the pump out of the lines and the fuel filter, where some of that sits after the engine has been run. That's why draining the tank yourself doesn't leave you sorted — a myth. It is also truly risky to drain petrol into a can at the roadside.
How does petrol in a diesel occur?
On purpose? Never. Through carelessness? Seldom, if ever. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slides into a diesel filler with almost no resistance, while a diesel nozzle mostly will not go into a petrol motor at all. So the slip runs one way.
It takes place when habit and the vehicle stop matching. Hire cars, courtesy cars, and motors that are new to you. Households running one of each, petrol and diesel. The pumps in a different order on a familiar forecourt. Fuelling up in a hurry en route to Beaulieu Park, with a train to catch. A new-to-you diesel Renault Megane, its first fuelling, and a motorist used to petrol: exactly when it occurs. Add a back seat full of children, a phone call or rain, and habit takes over.
How to prevent petrol in a diesel at your next fill-up in Boreham
- The label is what matters, and so check the petrol pump instead of the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt.
- In a motor you do not know, look inside the flap over the filler or at the cap before the first fill: many motors state the fuel type there.
- A coloured fob or a sticker on the diesel's key achieves more than any amount of intending to remember, in a house with one of each.
- Before the nozzle leaves the petrol pump the first time you fuel a hired or new car, say "diesel" out loud. Silly, perhaps, but it does the trick.
- Thinking about something else is when this becomes an easy mistake to make, so tuck your phone away then keep your mind on the petrol pump.
- Some diesels come with a filler built to refuse a petrol nozzle, and devices you can add exist for vehicles without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop reading the pump.
- Stop as soon as you notice. Less petrol inside your tank makes a thinner mixture. It does not change what to do next, which is still not to fire it up.
Put petrol in a diesel around Boreham already?
In that case, there is just a short order of things. Don't crank it, and don't turn your ignition on. Ask the attendants to help you push it away from the pump if you're still at the forecourt, whether that is BP or anywhere else. Next, 0333 366 0103. We'll ask what got in, about how much, and if it's been run.
Corrosion and deposits form the trouble with AdBlue, whereas petrol brings lost lubrication. So if it was AdBlue, say so — and read its own Boreham page.
Boreham petrol in a diesel jobs: why one costs more than another
A fair single price does not exist here: four situations, four separate tasks. Which of them you are in is chiefly what shifts the cost. The share matters next, meaning how much of that tank is petrol, followed by the location of the vehicle and whether reaching it is safe for a technician.
Ahead of any quote, not after, we ask three queries: your fuel that went in, its quantity, and if it has run. That's why. Those answers are what turn a range into one firm number.
About Boreham
Boreham is a village in Essex, situated approximately 3.7 miles from Chelmsford and 34 miles from London, with Boreham being a relatively small settlement at an elevation of 39 metres. Boreham has a mix of housing types, but semi-detached homes are predominant, and Boreham is surrounded by other villages such as Mowden, Hatfield Peverel, and Little Baddow. Boreham remains a quiet, inland community with a population of around 1624 residents.
Boreham and Essex: where our fuel drain cover runs
The vans answering petrol in diesel calls in Boreham, in the CM postcode area, equally work the spots near it, Mowden, Hatfield Peverel and Little Baddow included. The vehicle doesn't need to move to us: our technicians drain on a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Boreham: still at the pump?
Nothing beats it: that's where you now are. Turned off it remains; then call.