Should You Worry? Petrol in a Diesel Car in Keston Mark
Not started? Then less anxious than you likely feel. Petrol sitting in a diesel tank does nothing to your engine until something pulls it through the fuel system — the ignition priming the pump, your starter, or the drive on its own. So the truthful answer to the first query everyone in Keston Mark asks, "have I wrecked it?", is usually no. Petrol in Diesel is who to phone, with the motor kept off, and so it stays that way. The remainder of this page explains what petrol really does to a diesel, how to tell how far it has got, and how to make sure it doesn't happen to you a second time.
The motor and petrol in a diesel: what goes on
On its way through an engine, diesel has two jobs. It ignites, and before it burns it protects. What stops the surfaces inside the high-pressure fuel pump and the fuel injectors from wearing down against each other is your diesel passing through them — they are designed to very fine gaps.
Petrol does the first job poorly and the second not at all. It's runnier than diesel and strips away the lubrication your fuel system hinges on, and so a pump running on a petrol blend is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That's where the knocking comes from.
Taken together, they show the shape the problem has. Contact does not do the harm — movement does. Petrol in a tank is a fuel fault. The start of a mechanical one is a pump that has been running on that petrol — and whatever a worn pump sheds travels on with the fuel to the injectors downstream.
Four situations our technicians see around Keston Mark: how bad is petrol in a diesel?
The best case there is: filled up, not once started. That petrol is in the tank and only that tank, and the task is a drain and a flush where your car stands. This is the one situation that can only truly occur at a forecourt, because anywhere else your car has been driven to get there.
A brief spell of running, or merely the ignition on. Once primed, the system has drawn petrol from that tank as far as the fuel filter and the lines. Normally little more than draining, rinsing and seeing to the fuel filter, so still simple.
Those few miles on the road were your pump labouring on fuel diluted by petrol the whole way. Tank, lines, filter, then fresh fuel put through the whole circuit: that is this work, and the way the vehicle was driven matters as much as the mileage. On the school run to Keston Church of England Primary School, the miles is small. Very different once more: a run to London, under 15 miles away, or any mileage on the M25, under 5 miles from Keston Mark, where the motor kept labouring hard.
Driven until it protested. Knocking, a lumpy idle, smoke, a throttle that has gone soft. What you are hearing is the motor signalling fuel that no longer acts like diesel. Pull up wherever you are — the verge on Westerham Road, a lay-by, a side street — and leave the car there. A car stopped quickly very rarely has lasting damage, because the fuel drain and the flush-through, which still go first, deal with it.
Myths Keston Mark drivers hear about petrol in a diesel
False: topping up to full with diesel makes it fine. It does not. Nothing is removed when you top up — the tank just holds more of the same mixture. That advice presumes a diesel fuel system tolerates petrol by percentage. It does not.
"Current diesels can handle a little petrol" — a myth, and closer to the reverse. Protection matters more on current diesels, not less, because their fuel passes through finer parts at higher pressure.
One myth that catches people out: if it starts and drives, it must be unharmed. Feed diesel to a petrol motor and it generally won't run, so the driver stops — and the damage stops with them. Feed petrol to a diesel and it normally starts, idles and pulls away like nothing happened — all while its pump wears. Fine and running are not the same at all.
An outdated workaround for a different issue lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." That petrol is still in that tank afterwards, and whatever it has thinned is not put back.
The next start sends petrol back round the pump from the lines and the fuel filter, where some of it ends up after the motor has run. That is why draining your tank yourself does not leave you sorted — a myth. It is also really dangerous to drain petrol into a can by the roadside.
Petrol in a diesel: how does it happen?
On purpose? Never. Through carelessness? Seldom, if ever. A diesel nozzle generally will not fit a petrol car, 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 that direction.
It takes place when habit and the vehicle stop matching. Hire cars, courtesy cars, and vehicles that are new to you. A household with one petrol and one diesel on the drive. The pumps in a different order on a well-known forecourt. Filling up in a rush en route to Hayes (Kent), with a train to catch. Precisely the moment it takes place: after years of driving petrol, someone fills a diesel BMW 3 Series for the first time. Add rain, a phone call or a back seat full of kids, and the hand repeats what it has always done.
How to avoid petrol in a diesel at your next fill-up around Keston Mark
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, even if most generally do. Check the pump's label; the colour is just a clue.
- Check the filler flap. Many motors state the fuel type 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 the diesel's key does more than any amount of meaning to remember, for a house with one of each.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the pump. It seems daft and it does the trick.
- Put your phone away. This is an easy mistake to make while you're thinking about something else.
- Add-on devices exist for vehicles without one, and some diesels come with a filler that will not accept a petrol nozzle. Helpful — but a safety net only, never a reason to stop checking the label.
- Stop as soon as you realise. Less petrol inside your tank makes a weaker blend. It does not change what to do next, which is still not to start the car.
Petrol already in a diesel in Keston Mark? Begin here
Then, there's only a short order of things. Starting it is out, and so is turning on the ignition. The attendants on the forecourt — whether at the nearest petrol station itself or wherever you filled up — will normally help roll it clear of the petrol pump if you ask. Then phone 0333 366 0103 and tell us what went in, about how much, and if it has run.
Say so if it was AdBlue rather than petrol: it is a separate fault, with its own page for Keston Mark, because AdBlue brings corrosion and deposits instead of lost lubrication.
One petrol in a diesel job in Keston Mark costs more than another. Why?
The four scenarios above are four different jobs, so no single quote for this would be honest. Chiefly, the cost shifts with which situation you are in. The ratio matters next, meaning how much of your tank is petrol, and then the position of the vehicle and whether getting to it is safe for our van.
Before any quote, not after, we ask three questions: the fuel that went in, its volume, and whether it has run. That's why. Those answers change a range into a straight figure.
About Keston Mark
Keston Mark is a suburban area located on the riverside in Greater London, with an elevation of around 102 metres. Keston Mark sits near the towns of Keston, Locksbottom, and Bromley Common, and is approximately 12 miles from central London. Keston Mark is characterised by its predominantly detached housing stock, which reflects the area's residential nature. Keston Mark has a population of around 2430 people, according to recent estimates.
Across Greater London and in Keston Mark: fuel drain cover
Keston, Locksbottom and Bromley Common are among the locations near Keston Mark that the same teams work, answering petrol in diesel jobs across Keston Mark's BR postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all places our technicians work, and the vehicle doesn't need to come to us.
At the pump in Keston Mark, right now?
Then you're in the best spot there is. Leave the car turned off, and ring.