Motcombe: Petrol in a Diesel Car? How Worried to Be
Probably less than you already are — provided no one has started the vehicle. Everyone in Motcombe starts with "have I wrecked it?", and the fair answer is normally no: petrol resting inside the tank of any diesel stays harmless until priming, cranking or driving draws it into your fuel system. Petrol in Diesel is who to ring, with the motor kept off, and so it stays that way. What petrol really does to a diesel, how to judge how far it's gone, and how to keep it from happening a second time: that is the remainder of this page.
What petrol in a diesel does to the motor
Diesel does two jobs on its way through an engine. Oiling comes before burning; it does both. The high-pressure pump and your injectors are designed to extremely fine clearances, and the diesel passing through them is what stops those surfaces from wearing down against each other.
The second task petrol does not do at all, and the first it does badly. A pump working on a petrol mixture is wearing itself out, since petrol is thinner than diesel and takes away the protection your fuel system depends on. Petrol is also designed to resist igniting under compression — the reverse of what a diesel needs from its fuel — and that's where any clattering comes.
Put those together and the shape of the trouble is clear. Not contact but movement is what does the harm. All a tank with petrol in it amounts to is a fuel issue. A pump that has been labouring on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with the fuel to the fuel injectors further on.
How bad is petrol in a diesel? Four situations our engineers see in Motcombe
Filled but never started — the best it gets. On a forecourt, and genuinely only there, the petrol is still limited to the tank — since anywhere else the car was driven to get to it. The job is draining and rinsing on the spot.
The ignition turned on, or a short start. Your system has been primed, and so petrol has left that tank and got to the filter and your lines. Usually nothing more than emptying, purging and seeing to your filter, and so still straightforward.
The pump has spent a couple of miles on diluted fuel — that is what driving the car meant. Distance is only half of that; how hard it was driven counts equally. Either way the work includes that tank, your lines, your filter and fresh fuel through the entire circuit. Driving the kids to Motcombe CofE Primary School is one sort of trip. Very different a second time: a run to Salisbury, under 25 miles away, or any mileage on the M27, under 50 miles from Motcombe, where the motor never stopped working hard.
It complained, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone lumpy. What you are hearing is your engine signalling fuel that no longer runs like diesel. Pull up wherever you are — the verge on Glebe Gardens, a lay-by, a side street — and leave the car there. What goes first is still the fuel drain and flush, and that sorts it out, with lasting damage very rare if a vehicle is pulled over soon.
Petrol in a diesel stories Motcombe motorists hear
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing is removed by topping up — you're left with a bigger tank, still the same mix. A diesel fuel system does not tolerate petrol by percentage in the way that advice supposes.
If anything, the reverse is true. Myth: "A newer diesel can cope with a bit of petrol." More precise parts and higher pressure are the way a current diesel runs its fuel, and that makes the lubrication matter more, not less.
"It starts, it drives, so no harm done" — the myth that trips up more people than any other. The motorist of a petrol engine fed diesel usually stops, since it will not run, and the harm stops with them. Feed petrol to a diesel and it generally fires up, ticks over and drives away as if nothing happened — all while its pump is wearing. Running does not mean fine.
An outdated workaround for a separate fault lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." What petrol has diluted stays thinned, and that petrol stays inside that tank regardless.
Once the engine has been run, part of the petrol is in your filter and the fuel lines, not your tank — and your next start pulls it straight back through the pump. So the myth "drain that tank yourself and you are sorted" doesn't hold. Clearing petrol into a can by the kerbside is also genuinely hazardous.
How it happens: petrol in a diesel
On purpose? Never. Through carelessness? Seldom, if ever. One way only, because of the nozzles: the narrower petrol one slips inside a diesel filler with almost no resistance, while the diesel one mostly will not fit a petrol motor. That's how the forecourt makes it easy.
Habit and the car falling out of step is when it happens. Hire cars, courtesy cars, and motors that are new to you. Two motors 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 Gillingham (Dorset), with a train to catch. Precisely the moment it takes place: after years of driving petrol, someone fills a diesel Volkswagen Golf for the first time. Add rain, a phone call or a back seat full of children, and the hand repeats what it has always done.
Avoiding petrol in a diesel next time you fill up around Motcombe
- Read the petrol pump, not the colour. In the UK unleaded handles are generally green and diesel black, yet not on every forecourt. The label is what counts.
- Plenty of cars state the fuel type inside the filler flap or on the cap, so check there on the first fill in any motor you don't know.
- A coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember, in a house with one of each.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the pump. It seems daft and it does the trick.
- Thinking about something else is when this becomes an easy mistake to make, and so put your phone away then keep your mind on the pump.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler built to block a petrol nozzle, and add-on devices are available for the rest. Count it as a safety net, and keep checking the petrol pump.
- Noticing it mid-fill? Stop at once. A thinner blend follows from less petrol in the tank, yet your next stage remains the same: do not start the car.
Motcombe: already put petrol in a diesel?
Short and simple, then, is the order of things. Do not turn your ignition on, and don't crank it. Yet on the forecourt, at Murco or anywhere else? Ask the attendants to help you roll the vehicle away from the petrol pump. Phone 0333 366 0103 next, with three facts — your fuel, the approximate amount, and if it's run.
Say so if it was AdBlue instead of petrol: it is a different fault, with its own page for Motcombe, since AdBlue brings corrosion and deposits rather than lost lubrication.
Motcombe petrol in a diesel jobs: why one costs more than another
Four different jobs sit behind the four situations above — which is why there is no fair single quote. What moves your cost is mostly which of them you're in. Where the car is matters too, and whether a technician can safely reach it, after the ratio of petrol to what that tank takes.
Before any quote, not after, come three questions: your fuel that was put in, the amount, and if it's run. That's why. With those answers, there is a straight figure rather than a range.
About Motcombe
Motcombe is a small village in Dorset, situated inland at an elevation of around 88 metres, with detached housing being the predominant type of accommodation. Motcombe lies near the villages of Elm Hill, Bittles Green, and North End, and is approximately 18.5 miles from Salisbury. Motcombe has a population of around 713 residents, and is located about 96 miles west of London. Motcombe remains a quiet rural community with a strong sense of local identity.
Motcombe and Dorset: where our fuel drain cover reaches
The teams answering petrol in diesel calls around Motcombe, in the SP postcode area, also work the places near it, Elm Hill, Bittles Green and North End among them. A forecourt, a supermarket car park, a lay-by or your own driveway are all spots our technicians drain, and the vehicle doesn't need to move to us.
In Motcombe and still at the pump?
No position is better: that's where you now are. Phone, and leave it switched off.