The Close: Petrol in a Diesel Car? How Worried to Be
Far less than you likely are, provided it has not been started. "Have I wrecked it?" is the first thing anyone around The Close asks, and the honest answer is usually no, since petrol left in a diesel tank harms nothing till it's drawn through your fuel system — by ignition priming, by your starter, or by being driven. To leave the car that way, ring Petrol in Diesel then leave the motor switched off. Keep reading for three things: the effect petrol has inside a diesel motor, the signs of how far it has got, and ways to make sure you never repeat it.
What petrol in a diesel does to your engine
Passing through an engine, diesel does two jobs at once. Before it burns, it lubricates — and then it combusts. Designed to extremely fine clearances, your injectors and the pump depend on the diesel flowing through them to keep their surfaces from wearing against one another.
Petrol handles the first task poorly and the second not at all. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump on the blend to wear itself. It is also made to resist igniting under compression — the opposite of what a diesel needs — which is where you get the rattling.
Taken together, they show what shape the issue takes. Not contact but circulation is what does the damage. Where that petrol is only in your tank, it is an issue of fuel, nothing more. A pump that has been running on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the fuel injectors downstream.
Four scenarios our technicians see in The Close: how serious is petrol in a diesel?
Fuelled but not once started — as good as it gets. At a forecourt, and really only there, that petrol is still limited to your tank — because anywhere else the car was driven to get to it. The task is emptying and purging on the spot.
Ignition on, or started for a moment. Your system has been primed, and so petrol has left your tank and reached your filter and the lines. Drain, flush, see to your filter: still usually easy.
The pump now worked a few miles on diluted fuel — that is what driving the vehicle does. Tank, lines, filter, then fresh fuel put through the entire system: that is this work, and the way your car was driven counts as much as the mileage. Driving the kids to All Saints Church of England Primary School is one kind of trip. A run as far as Winchester, under a mile away, is a very different job. So is any distance on the M3, under a mile from The Close, where the engine has been working hard throughout.
Driven till it complained. Knocking, a lumpy idle, smoke, a throttle that has gone soft. The motor is telling you the fuel is no longer behaving like diesel. Whether it's the verge on St Swithun Street, a lay-by or a side street, stop where you are then leave it. A vehicle pulled over quickly very rarely has lasting damage, because the fuel drain and the flush, which still come first, deal with it.
Stories The Close people hear about petrol in a diesel
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. Topping up takes out nothing; it gives you a bigger tank of the same mix. A diesel fuel system does not tolerate petrol by percentage in the way that guidance presumes.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. At higher pressure, through more precise parts: that is how a newer diesel handles its fuel, and so the lubrication matters for more, not less.
This is the one that fools drivers. Myth: "If it starts and drives, there is no damage done." Any petrol engine fed diesel usually will not run, and so the motorist stops and the harm stops with them. Feed petrol to a diesel and it usually starts, idles and drives away as if nothing has happened — all while its pump wears. Running doesn't mean fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a different issue. It doesn't put back what petrol has diluted, and that petrol is still in that tank after that.
Once the motor has run, part of the petrol is in your filter and the fuel lines, not your tank — and your next start sends it right back through your pump. So the myth "drain that tank yourself and you are sorted" does not hold. Besides, petrol drained into a can by the road is genuinely risky.
Petrol in a diesel: how does it take place?
Nobody does it on purpose, and it is seldom carelessness. A diesel nozzle generally won't go into a petrol vehicle, yet the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake simple, and just in one direction.
Habit and the car getting out of step is when it occurs. Hire cars, courtesy cars, and cars that are new to you. Two motors on one driveway, one petrol, one diesel. Your usual forecourt, its pumps suddenly in a different order. Filling up in a hurry en route to Winchester, with a train to catch. A new-to-you diesel Skoda Octavia, its first fuelling, and a motorist accustomed to petrol: exactly when it takes place. With rain, a call arriving, or a car full of children to deal with, the hand just does what it always has.
The Close people: how to prevent petrol in a diesel next time
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on each forecourt. The label is what counts.
- Check your filler flap. Many motors state the fuel inside the flap or on the cap. Look at it on the first fill in any car you do not know.
- A coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember, in a home with one of each.
- Before the nozzle leaves the pump the first time you fuel a hired or new vehicle, say "diesel" aloud. Silly, perhaps, but it does the trick.
- Put the phone away. This is an easy mistake to make whilst you're thinking about something else.
- Some diesels have a filler built to block a petrol nozzle, and devices you can add are available for vehicles without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop reading the pump.
- The moment you notice, stop: less petrol inside the tank means a thinner blend. What to do next doesn't change, though — still do not fire it up.
The Close: already put petrol in a diesel?
In that case, there is just a short order of things. Don't crank it, and do not switch the ignition on. If you are still at the forecourt — BP or anywhere else — ask the attendants to help you roll the vehicle away from the pump. Call 0333 366 0103 next, with three facts — the fuel, the rough amount, and if it has run.
Say so if it was AdBlue instead of petrol: it's a different problem, with its own page for The Close, because AdBlue brings corrosion and deposits instead of lost protection.
Why one petrol in a diesel job around The Close costs more than another
The four scenarios above are four separate tasks, so no single quote for this would be fair. Which of them you are in is chiefly what shifts the cost. Two things follow that: the petrol that was put in as a proportion of what your tank holds, then the spot the vehicle is in and whether a technician can get to it safely.
Ahead of any quote, not after, come three questions: your fuel that was put in, its amount, and whether it has run. That's why. Those answers change a range into a straight figure.
About The Close and its setting
The Close is a suburban area situated on the riverside in Hampshire, with The Close being adjacent to the city of Winchester. The Close has an elevation of 36 metres and is located approximately 59.9 miles from London. The Close is characterized by its predominant housing type, which is flats, and is part of the wider Winchester urban area.
Across Hampshire and around The Close: fuel drain cover
Winchester, Wharf Hill and The Soke are among the spots around The Close that the same teams work, answering petrol in diesel calls across The Close's SO postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all places our technicians drain, and your car doesn't need to move to us.
Still at the petrol pump around The Close?
The best position there is, then — that is where you are. Call, and keep it turned off.