How Worried Should You Be? Petrol in a Diesel Car in Pendeen
Less than you probably are, if it hasn't been started. Everyone in Pendeen begins with "have I ruined it?", and the honest answer is usually no: petrol left inside your tank of any diesel stays harmless until priming, cranking or driving pulls it into your fuel system. Keep it like that: leave your engine off and ring Petrol in Diesel. What petrol actually does to a diesel, how to gauge how far it's travelled, and how to stop it from happening again: that is the remainder of this page.
What petrol in a diesel does to the engine
On its way through an engine, diesel does two jobs. It lubricates to begin with, and only then does it burn. Built to very fine gaps, the injectors and your pump rely on your diesel moving through them to stop their surfaces wearing against one another.
Badly at the first, not at all at the second: that's petrol. It is runnier than diesel and strips away the protection the system depends 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 reverse of what a diesel needs from its fuel. That's where the knocking comes from.
Taken together, they make clear the shape the issue has. The damage is done by circulation, not by contact. Petrol in the tank is a fuel fault. Whatever a worn pump sheds travels on, carried by the fuel, into your injectors further along, which is why a pump that has worked on that petrol is where a mechanical issue begins.
How serious is petrol in a diesel? Four scenarios our engineers see in Pendeen
Fuelled but not once started — the best it gets. The petrol is in your tank and just your tank, and the job is a drain and a flush where your car sits. This is the one scenario that can only really occur on a forecourt, because anywhere else the vehicle has been driven to get there.
Ignition on, or started for a moment. The fuel system has been bled, so petrol has left the tank and reached the fuel filter and the fuel lines. Normally little more than clearing, cleaning and sorting your filter, so still straightforward.
Your pump now worked a couple of miles on diluted fuel — that's what driving the vehicle does. The work is your tank, the fuel lines, the filter and clean fuel through the whole circuit, and how hard the vehicle was driven matters as much as how far. The school run to Pendeen School is one thing. Very different once more: a trip to Truro, under 50 miles away, or some mileage on the M5, over 50 miles from Pendeen, where the motor never stopped labouring hard.
It protested, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone uneven. What you are hearing is your motor reporting fuel that no longer runs like diesel. Leave it where it stops: a lay-by, a side street, the verge on B3306. What goes first is still the drain and flush, and that sorts it out, with lasting damage very unusual when a car is stopped soon.
Stories Pendeen people hear about petrol in a diesel
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 are left with a fuller tank, still the same mix. A diesel fuel system does not accept petrol by percentage in the way that guidance supposes.
If anything, the reverse holds. Myth: "A current diesel can cope with a bit of petrol." Finer components and higher pressure are the way a newer diesel runs its fuel, and that makes the lubrication matter more, not less.
Myth: "If it starts and drives, there is no damage done." This is the one that catches people. A petrol engine fed diesel generally will not run, and so the driver stops and the damage stops with them. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually will; meanwhile your pump wears. Running does not mean fine.
Myth: a two-stroke additive lets you to drive home. It was an old fix, supposed for another problem. None of what petrol weakened is put back by it — and afterwards, the tank still holds the petrol.
The next start draws petrol back round the pump from the lines and the filter, where some of it sits after the motor has been run. That is why draining your tank yourself doesn't sort it — a myth. Draining petrol into a can at the kerbside is also genuinely risky.
Why petrol in a diesel happens at all
On purpose? Never. Through carelessness? Seldom, if ever. The forecourt makes it easy: the petrol nozzle is the narrower of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle generally won't go into a petrol motor at all. So the mistake runs one way.
The moment routine stops matching the car is the moment it takes place. Any car that's new to you — hired, on loan as a courtesy car, or brand new. Households running one of each, petrol and diesel. A familiar forecourt with the pumps in a different order. Rushing for a train at Penzance and fuelling up en route. Years of petrol vehicles behind you, a diesel Volkswagen Golf in front of you at the forecourt for its first tank — that is when. Your hand does what it has always done when you add rain, a phone call or a back seat full of children.
Preventing petrol in a diesel next time you fill up around Pendeen
- Check the petrol pump, not the colour. In the UK unleaded handles are normally green and diesel black, but not on each forecourt. The label is what matters.
- In a vehicle you do not know, look inside the flap over your filler or at the cap before your first fill: many motors print the fuel type there.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of meaning to remember, for a home with one of each.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the pump. It sounds silly and it works.
- Thinking about something else is when this becomes an easy mistake to make, so tuck your phone away then keep your mind on the pump.
- Add-on devices exist for cars without one, and some diesels are built with a filler that won't take a petrol nozzle. Useful — but a backstop at best, never a reason to stop checking the label.
- Less petrol means a thinner mixture, and so stop the moment you notice — though remembering that the next stage is unchanged. It's still not to crank it.
Petrol already in a diesel around Pendeen? Begin here
The order of things is brief, then. Starting it is out, and so is turning on the ignition. The attendants on the forecourt — whether at Trewellard Garage itself or wherever you filled up — will normally help roll it away from the pump if you ask. Ring 0333 366 0103 next, with three facts — your fuel, the approximate volume, and if it's run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost protection, make it a different problem — Pendeen has a page all for it.
Pendeen petrol in a diesel jobs: why one costs more than another
The four situations above are four separate tasks, so no single quote for this would be honest. The scenario itself does most of the work of moving your cost. The ratio counts next, meaning how much of that tank is petrol, and then the location of your car and whether reaching it is safe for a technician.
What was put in, how much, and if it's run — three questions our engineers ask before costing, not after, for precisely that reason. Those replies turn a range into a straight figure.
About Pendeen
Pendeen is a small coastal village in Cornwall, situated on the Atlantic coast at an elevation of 131 metres. Pendeen sits near the villages of Higher Boscaswell and Lower Boscaswell, and is close to the coastal spot of Portherras. Pendeen has a population of around 1020 people, predominantly living in terraced housing, and is located approximately 28 miles from the city of Truro.
Fuel drain cover across Cornwall, Pendeen included
Higher Boscaswell, Lower Boscaswell and Portherras are among the spots near Pendeen that the same vans work, answering petrol in diesel calls across Pendeen's TR postcode area. The car doesn't need to move to us: our engineers drain at a forecourt, in a supermarket car park, in a lay-by or on your own drive.
Pendeen: still at the pump?
No position is better: that is where you now are. Leave the vehicle turned off, and ring.