Should You Worry? Petrol in a Diesel Car in Gwehelog Common
Unstarted? Then less worried than you likely feel. "Have I ruined it?" is the first thing anyone around Gwehelog Common asks, and the honest answer is generally no, because petrol left in a diesel tank hurts nothing until it's drawn through the system — by ignition priming, by your starter, or by being driven. Petrol in Diesel is who to phone, with the motor left off, and so it remains that way. Below, this page sets out what petrol really does inside a diesel, how far it might have gone, and how to stop it happening to you a second time.
What petrol in a diesel does to the motor
Passing through an engine, diesel is doing two things at once. It burns, and before it ignites it lubricates. The high-pressure pump and your injectors are designed to extremely fine gaps, and the diesel passing through them is what stops those surfaces from grinding against each other.
The second job petrol does not do at all, and the first it does badly. Being less viscous than diesel, petrol strips out the protection a fuel system needs, leaving a pump running on the blend to wear itself. It is also made to resist igniting under compression — the reverse of what a diesel needs — which is why you hear the rattling.
The shape of the issue is clear when you put those together. Not contact but movement is what causes the harm. Petrol in the tank is a fuel fault. A pump that has been running on that petrol is the start of a mechanical one, and whatever a worn pump sheds travels on with the fuel to the injectors further on.
Gwehelog Common, petrol in a diesel: four cases, from mild to serious
Fuelled, and not started: nothing beats it. Being on a forecourt is what makes this the case: elsewhere, the car has been driven there to begin with. With that petrol held inside that tank alone, it is emptied and flushed right where it stands, and nothing more is needed.
A brief spell of running, or merely the ignition on. Your system has been bled, and so petrol has left the tank and reached your filter and the fuel lines. That's normally still a straightforward job — a drain, a flush, and your filter dealt with.
The pump now spent a couple of miles on thinned fuel — that is what driving the vehicle does. How hard the vehicle was driven counts as much as how far, and the work takes in that tank, the lines, the fuel filter and fresh fuel through the whole circuit. Driving the kids to the local primary school is one kind of trip. Getting as far as Newport, under 15 miles away, makes a very different task — as does any mileage on the M4, under 10 miles from Gwehelog Common, with the engine labouring hard all the way.
Driven till it complained. Rattling, a ragged idle, smoke, a throttle that has gone soft. The fuel is not acting like diesel any more, and the motor is saying so. Leave it where it stops: a lay-by, a quiet street, the verge on Monmouth Road. What goes first is still the drain and flush-through, and that deals with it, with permanent damage very uncommon when a vehicle is stopped quickly.
What Gwehelog Common people get told about petrol in a diesel — and the myths in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." Topping up takes out nothing; it gives you a fuller tank of the same mix. The idea behind that advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
If anything, the reverse is true. Myth: "A newer diesel can cope with a bit of petrol." A modern diesel sends its fuel through finer parts at higher pressure, which makes the lubrication matter more, not less.
This is the one that catches people. Myth: "If it starts and drives, there's no damage done." Diesel in a petrol motor usually means a motor that will not run: the driver stops, and so does the damage. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually will; meanwhile your pump grinds. Running doesn't mean fine.
An outdated fix for a distinct problem lies behind this one. Myth: "Add some two-stroke oil and drive the car home." That petrol is still inside the tank afterwards, and what it has thinned is not put back.
Once the motor has run, part of that petrol is in the fuel filter and the fuel lines, not your tank — and the next start pulls it right back through the pump. So the myth "drain that tank yourself and you're sorted" doesn't hold. It is also really risky to drain petrol into a can by the roadside.
Petrol in a diesel: how does it occur?
Carelessness is seldom the cause, and no one means to do it. The petrol nozzle is the smaller of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol vehicle at all. The forecourt makes it easy, and the mistake runs one way.
It happens when routine and the vehicle stop matching. A new motor, a hire car or a courtesy car. One petrol and one diesel on the drive of the same household. A forecourt you know, but with its pumps arranged differently. A rushed fill on the way to Pontypool and New Inn with a train to catch. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is exactly the moment it happens. With rain, a call coming in, or a car full of children to deal with, your hand just does what it always has.
Next time you fill up around Gwehelog Common: avoiding petrol in a diesel
- The label is what matters, so read the petrol pump rather than the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt.
- The first fill in a new vehicle is the time to check your filler flap — inside it, or on the cap, plenty of cars state the fuel they take.
- A coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember, in a house with one of each.
- Before the nozzle leaves the petrol pump the first time you fill a hired or new car, say "diesel" out loud. Daft, perhaps, yet it does the trick.
- Mistakes like this are straightforward to make whilst your mind is on something else, so the phone goes away.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler designed to block a petrol nozzle, and aftermarket devices exist for the rest. Treat it as a safety net, and keep checking the petrol pump.
- Stop as soon as you realise. Less petrol inside your tank means a thinner blend. It does not change what to do next, which is still not to crank it.
Put petrol in a diesel around Gwehelog Common already?
Then the order of things is brief. Do not fire it up, and do not switch the ignition on. Yet at the forecourt, at BP or anywhere else? Ask the staff to help you push the vehicle clear of the pump. Then ring 0333 366 0103 and tell us what went in, roughly how much, and whether it has run.
Say so if it was AdBlue rather than petrol: it is a different issue, with its own page for Gwehelog Common, because AdBlue brings corrosion and deposits rather than lost protection.
Why one petrol in a diesel job around Gwehelog Common costs more than another
Four different tasks lie behind the four situations above — which is why there is no fair single price. Which of them you're in is chiefly what shifts your cost. Where your car is matters too, and whether a technician can safely reach it, after the proportion of petrol to what the tank takes.
Ahead of any quote, not after, come three queries: the fuel that went in, its amount, and if it has run. That is why. Their answers are what turn a range into one firm number.
About Gwehelog Common itself
Gwehelog Common is a small village situated on the banks of a river in Monmouthshire, with a mix of rural and natural environments. Gwehelog Common has a relatively low elevation of 117 metres and is located near several other small villages and common land areas, including Gwehelog and Trostrey Common. Gwehelog Common is characterized by its predominantly detached housing stock and is within commuting distance of Newport, the nearest city. Gwehelog Common is also close to popular walking routes, such as the Llandenny Walks.
Gwehelog Common and Monmouthshire: where our fuel drain cover runs
Gwehelog, Trostrey Common and Llandenny Walks are among the places around Gwehelog Common that the same teams work, answering petrol in diesel calls across Gwehelog Common's NP postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations our engineers drain, and your car does not need to come to us.
At the petrol pump around Gwehelog Common, right now?
Nothing beats it: that's where you now are. Keep the vehicle switched off, then ring.