How Worried Should You Be? Petrol in a Diesel Car in Hirael
Not started? Then less worried than you likely feel. "Have I wrecked it?" is the first thing anyone around Hirael asks, and the honest answer is normally no, because petrol left in a diesel tank harms nothing till it is drawn through your fuel system — by ignition priming, by your starter, or by being driven. To leave the car like that, ring Petrol in Diesel and leave your engine alone. Below, this page sets out what petrol actually does inside a diesel, how far it might have gone, and how to stop it happening to you a second time.
Inside the engine: what petrol in a diesel really does
On its way through a motor, diesel has two jobs. Before it ignites, it protects — and then it combusts. What stops the surfaces inside the high-pressure pump and your injectors from wearing against each other is the diesel passing through them — they're made to extremely fine gaps.
The second job petrol does not do at all, and the first it does poorly. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump running 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.
Seen together, they show what shape the problem has. It is circulation that causes the damage, not contact. Petrol in the tank is a fuel problem. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with your fuel to your injectors further on.
Hirael, petrol in a diesel: four cases, from mild to major
The best case there is: filled up, never started. The petrol is inside that tank and only your tank, and the task is a drain and a flush where the car sits. This is the one scenario that can only truly take place on a forecourt, because anywhere else the vehicle has been driven to get there.
A moment's running, or merely the ignition on. Petrol has come out of that tank and got to your filter and the fuel lines, since the system has been bled. Drain, flush, see to the filter: still usually easy.
Your pump has spent a few miles on thinned fuel — that is what driving the vehicle meant. Miles is only half of it; how hard it was driven matters equally. Either way this work includes your tank, your lines, the filter and clean fuel through the whole system. Driving the kids to the local primary school is one sort of trip. Getting as far as Bangor, under a mile away, makes a very different job — as does any distance on the Moreton Spur, under 50 miles from Hirael, with your engine working hard all the way.
It protested, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone ragged. What you are hearing is the motor reporting fuel that no longer behaves like diesel. Stop wherever you are — the verge on Stryd Robert, a lay-by, a side street — and leave the car where it is. What comes first is still the fuel drain and flush, and that deals with it, with lasting damage very rare if a car is stopped quickly.
Myths Hirael 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. Nothing is removed by topping up — you're left with a bigger tank, still the same mix. The idea behind the advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Modern diesels can handle a little petrol" — a myth, and nearer the opposite. A modern diesel runs its fuel through smaller parts at higher pressure, which makes the protection count more, not less.
This is the one that catches people. Myth: "If it starts and drives, there's no damage done." The motorist of a petrol motor fed diesel normally stops, because it will not run, and the harm stops with them. A diesel fed petrol usually starts, idles and drives away as if nothing has happened, while your pump grinds. Running isn't the same as fine.
An outdated fix for a separate problem is behind this one. Myth: "Add some two-stroke oil and drive it home." It doesn't put back what petrol has diluted, and the petrol is still in your tank afterwards.
Myth: "Drain the tank yourself and you are sorted." Once the engine has been run, some of the petrol is no longer inside the tank: it is in your filter and the lines, and it goes right back through the pump at the next start. On top of that, petrol emptied into a can by the road is genuinely risky.
Petrol in a diesel: how does it occur?
Carelessness is seldom the cause, and nobody means to do it. One way only, because of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, while the diesel one generally won't fit a petrol motor. That is how the forecourt makes it easy.
When habit and your car stop matching, it takes place. Courtesy car, hire car, or a car that is new. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a familiar forecourt. Fuelling up in a hurry on the way to Bangor (Gwynedd), with a train to catch. Exactly the moment it occurs: after years of driving petrol, someone fills a diesel Renault Megane for the first time. With rain, a call arriving, or a car full of children to deal with, your hand simply does what it always has.
Next time you fill up in Hirael: avoiding petrol in a diesel
- Check 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 matters.
- The first fill in an unfamiliar motor is the time to check your filler flap — inside it, or on the cap, plenty of motors state the fuel they take.
- A coloured fob or a sticker on your diesel's key does more than any amount of intending to remember, for a house with one of each.
- "Diesel", aloud, before you lift the nozzle — every time a new or hired car gets its first tank. It sounds daft. It works.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck the phone away.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler designed to reject a petrol nozzle, and add-on devices are available for vehicles without one. They are a backstop, not a reason to stop checking the pump.
- Less petrol means a thinner blend, and so stop the moment you notice — while remembering that your next step is unchanged. It's still not to crank it.
Put petrol in a diesel around Hirael already?
Short and simple, then, is the order of things. Don't turn the ignition on, and do not start it. Yet on the forecourt, at BP or anywhere else? Ask the staff to help you roll it clear of the petrol pump. What got in, roughly how much, and whether it's run: tell us those when you ring 0333 366 0103.
If it was AdBlue rather than petrol, say so. That is a separate problem — corrosion and deposits rather than lost lubrication — and it has its own page for Hirael.
One petrol in a diesel task around Hirael costs more than another. Why?
Four separate tasks sit behind the four situations above — which is why there's no fair single quote. Mostly, the cost shifts with which situation you are in. The proportion counts next, meaning how much of your tank is petrol, followed by the position of your car and whether reaching it is safe for a technician.
Before any quote, not after, come three queries: the fuel that was put in, the quantity, and whether it's run. That's why. Their answers are what turn a range into one firm number.
About Hirael, briefly
Hirael is a coastal suburban area in northwest Wales, situated near the city of Bangor and close to the Menai Strait. Hirael is characterized by its predominantly terraced housing and relatively low elevation of 11 metres above sea level. Hirael is bordered by nearby places such as Garth and Maesgeirchen, and is part of the larger Bangor urban area.
Hirael and Gwynedd: where our fuel drain cover reaches
Hirael waits in the LL postcode area, and the teams that answer petrol in diesel call-outs there work the locations around it as well — Garth, Maesgeirchen and Bangor among them. The vehicle doesn't need to come to us: our technicians drain at a forecourt, in a supermarket car park, in a lay-by or on your own drive.
In Hirael and still at the petrol pump?
Then, you couldn't be in a better spot. Keep it off. Ring.