Alstone: Petrol in a Diesel Car? How Worried to Be
Probably less than you already are — provided nobody has started it. Until the ignition primes your pump, the starter turns, or the car is driven, petrol in a diesel tank simply sits there and does nothing. Which makes the truthful reply to that first Alstone query — "have I ruined it?" — usually no. Keep it like that: leave your engine off and call Petrol in Diesel. The remainder of this page covers what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it does not happen to you again.
What petrol in a diesel does to your engine
On its way through a motor, diesel does two jobs. Oiling comes before burning; it does both. Your high-pressure pump and the fuel injectors are made to extremely fine gaps, and the diesel passing through them is what stops those surfaces from wearing down against one another.
Of these two tasks, petrol handles the first poorly and the second never. Being less viscous than diesel, petrol strips away the protection a fuel system needs, so a pump on the blend wearing itself. It's equally made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the knocking.
Together, those leave the shape of the issue clear. The damage is done by circulation, not by contact. Petrol in the tank is a fuel fault. A pump that has been working on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with your fuel to the injectors downstream.
Alstone, petrol in a diesel: four situations, from mild to major
Filled up, not once started. The best case there can be. Just your tank has petrol in it, and so the task is draining your tank and cleaning your system where the vehicle stands. This scenario can only truly occur on a forecourt: anywhere else, the vehicle got there by being driven.
Your ignition turned on, or a brief start. Petrol has left that tank and reached the fuel filter and the lines, because the system has been bled. Usually nothing more than emptying, purging and sorting the filter, so still simple.
Driven a few miles. Now your pump has spent those miles running on diluted fuel. Tank, lines, filter, then fresh fuel put through the whole circuit: that's this work, and the way the vehicle was driven counts as much as the mileage. Short trips, such as the school run to West Huntspill Primary Academy, are one thing. Any distance on the M5, under a mile from Alstone, means your engine has worked hard throughout, and a run to Wells, under 15 miles away, makes a very different task too.
Driven on until it complained — knocking, smoke, a lumpy idle, a dead throttle. That's the engine telling you its fuel has stopped behaving like diesel. Whether it is the verge on Adams Close, a lay-by or a side road, stop there then leave it. The drain and flush still go first, and they sort it out: when a vehicle is stopped soon, permanent damage is very uncommon.
Petrol in a diesel stories Alstone motorists hear
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Topping up takes out nothing; it gives you a bigger tank of the same mixture. The idea behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
If anything, the reverse is true. Myth: "A current diesel can cope with a bit of petrol." Lubrication counts more on modern diesels, not less, since their fuel runs through more precise parts at higher pressure.
Myth: "If it starts and drives, there is no harm done." This is the one that fools motorists. The driver of a petrol motor fed diesel normally stops, because it will not run, and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually will; meanwhile the pump grinds. Being able to run is not the same as being fine.
Myth: "Add some two-stroke oil and drive it home." It is an old workaround for a distinct problem. The petrol is still inside the tank afterwards, and whatever it has diluted is not put back.
The next start draws petrol back round the pump out of the fuel lines and your filter, where some of that ends up once the motor has run. That's why draining the tank yourself doesn't sort it — a myth. Draining petrol into a can at the kerbside is also genuinely hazardous.
Petrol in a diesel: how does it happen?
Carelessness is rarely the cause, and no one means to do it. The petrol nozzle is the slimmer of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol vehicle at all. The forecourt makes it easy, and the slip runs one way.
Habit and the vehicle falling out of step is when it occurs. Courtesy car, hire car, or a motor that is brand new. A household with one petrol and one diesel on the drive. The pumps in a different order on a familiar forecourt. A train to catch, and a rushed fill en route to Highbridge & Burnham. A new-to-you diesel Volkswagen Passat, its first fuelling, and a motorist accustomed to petrol: precisely when it occurs. Add rain, a phone call or a back seat full of children, and the hand does what it has always done.
Alstone drivers: how to prevent petrol in a diesel next time
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most generally do. Read the petrol pump's label; the colour is just a hint.
- The first fill in an unfamiliar vehicle is the time to check your filler flap — inside it, or on the cap, many vehicles state which fuel to use.
- A coloured fob or a sticker on the diesel's key achieves more than any amount of intending to remember, in a home with one of each.
- It seems daft and it does the trick: on the first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the petrol pump.
- Mistakes like this are straightforward to make whilst your mind is on something else, so the phone goes away.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler designed to refuse a petrol nozzle, and add-on devices are available for vehicles without one. They are a safety net, not a reason to stop checking the pump.
- As soon as you notice, stop: less petrol in the tank makes a thinner blend. What to do next doesn't change, though — still don't start it.
Alstone: already put petrol in a diesel?
Short and simple, then, is the order of things. Do not switch your ignition on, and do not start it. If you are still on the forecourt — Bunscome Garage or anywhere else — ask the staff to help you roll it clear of the petrol pump. What was put in, about how much, and whether it's run: tell us that when you phone 0333 366 0103.
If it was AdBlue rather than petrol, say so. That is a different fault — corrosion and deposits and not lost protection — and it has its own page for Alstone.
Why one petrol in a diesel task around Alstone costs more than another
An honest single price does not exist here: four situations, four separate tasks. The situation itself does most of the work of moving the cost. Two things follow that: the petrol that went in as a share of what the tank takes, then the spot the car is in and whether a technician can reach it safely.
That's why our technicians ask three questions before pricing instead of after: what was put in, how much, and if it's run. Their replies are what turn a range into one firm number.
About Alstone
Alstone is a small village in Somerset, situated near the coast and close to the nearby places of Highbridge and Huntspill. Alstone has a population of around 802 people and is characterised by predominantly detached housing. Alstone sits at a low elevation of 6 metres above sea level, looking out towards the Bristol Channel. Alstone is located near the city of Wells, which is 14.5 miles away.
Alstone and Somerset: where our fuel drain cover reaches
The teams answering petrol in diesel calls around Alstone, in the TA postcode area, equally work the spots near it, Highbridge, Huntspill and Hackness among them. You need not bring the vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all spots we drain.
In Alstone and still at the pump?
The best place there is, then — that is where you are. Turned off it stays; then ring.