Dulwich: Petrol in a Diesel Car? How Worried to Be
Provided it hasn't been started, worry far less than you probably are. Petrol resting in a diesel tank does nothing to your motor until something draws it through your fuel system — the ignition priming the pump, your starter, or driving itself. So the fair answer to the first question everyone in Dulwich asks, "have I ruined it?", is usually no. To keep the car like that, call Petrol in Diesel and leave your engine switched off. Further down, 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 again.
Inside the engine: what petrol in a diesel does
On its way through a motor, diesel does two tasks. It lubricates to begin with, and after that does it burn. Designed to very fine gaps, the fuel injectors and your pump depend on your diesel moving through them to stop their surfaces wearing against one another.
Badly at the first, not at all at the second: that is petrol. It's thinner than diesel and takes away the lubrication the system depends on, so a pump running on a petrol mix is a pump wearing itself. And petrol is made to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That's where the knocking comes from.
Taken together, they show what shape the problem takes. Not contact but circulation is what does the harm. Petrol in a tank is a fuel fault. After your pump has been running on that petrol, a mechanical fault has begun: anything shed by a pump that's grinding is carried onward to the fuel injectors with your fuel.
Petrol in a diesel around Dulwich: how serious is it? Four cases
The best case there is: filled up, not once started. Being on a forecourt is what makes this possible: elsewhere, the vehicle has been driven there to begin with. With the petrol held in the tank alone, it is drained and cleaned right where it stands, and nothing more is needed.
Your ignition turned on, or a brief start. Petrol has left the tank and got to the fuel filter and your lines, since the system has been primed. Still normally straightforward: drain, flush, and your filter seen to.
Those few miles on the road were the pump working on fuel thinned by petrol the whole way. The work is your tank, your lines, the filter and fresh fuel through the whole system, and how hard the car was driven counts as much as how far. On the school run to Dulwich Wood Primary School, the mileage is short. Driving as far as Westminster, under 5 miles away, makes a very different task — as does any distance on the M4, under 10 miles from Dulwich, with the motor running hard all the way.
Knocking, a lumpy idle, smoke, a throttle gone soft: driven till it complained. That's the motor telling you its fuel no longer is behaving like diesel. Leave it where it stops: a lay-by, a quiet street, the verge on Stonehills Court. What goes first is still the drain and flush, and that deals with it, with lasting damage very uncommon when a car is stopped early.
Myths Dulwich people hear about petrol in a diesel
False: topping up to full with diesel makes it fine. It doesn't. Topping up takes out nothing; it gives you a bigger tank of the same mixture. A diesel fuel system does not accept petrol by percentage in the way that advice assumes.
Not so: a modern diesel copes with a bit of petrol. Rather, the reverse. A newer diesel runs its fuel through more precise components at higher pressure, which makes the protection count more, not less.
This is the one that fools drivers. Myth: "If it starts and drives, there's no damage done." The driver of a petrol motor fed diesel usually stops, since it will not run, and the harm stops with them. Feed petrol to a diesel and it usually fires up, idles and pulls away like nothing happened — all while its pump is wearing. Running isn't the same as fine.
Myth: "Add some two-stroke oil and drive the car home." It is an old workaround for a separate fault. It does not put back what petrol has thinned, and that petrol is still in the tank after that.
If the motor has been run, part of that petrol is in the fuel filter and your lines, not the tank — and the next start sends it straight back through the pump. So the myth "drain the tank yourself and you are sorted" doesn't stand up. And, a can of petrol drained by the roadside is genuinely dangerous.
Why petrol in a diesel occurs at all
Nobody does it on purpose, and it is rarely carelessness. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slides into a diesel filler with almost no resistance, while a diesel nozzle mostly won't go into a petrol vehicle at all. So the slip runs one way.
The moment routine stops matching the vehicle is the moment it takes place. A new motor, a hire car or a courtesy car. Two vehicles on one driveway, one petrol, one diesel. A forecourt you know, but with its pumps arranged differently. A train to catch, and a rushed fill on the way to Sydenham Hill. A new-to-you diesel Renault Megane, its first fuelling, and a motorist used to petrol: precisely when it happens. Add a back seat full of children, a phone call or rain, and the hand wins.
How to avoid petrol in a diesel on your next fill-up around Dulwich
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, even if most usually do. Read the pump's label; the colour is only a clue.
- Check your filler flap. Many motors state the fuel inside the flap or on the cap. Look at it on your first fill in any vehicle you don't know.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of intending 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" out loud before you lift the nozzle off the pump. It seems silly and it works.
- While you are thinking about something else, this is an easy mistake to make — so put your phone away.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler built to block a petrol nozzle, and add-on devices exist for motors without one. They are a backstop, not a reason to stop checking the pump.
- Noticing it halfway? Stop at once. A thinner mixture follows from less petrol inside that tank, yet the next step remains the same: do not start the car.
Petrol already in a diesel in Dulwich? Start here
Then the order of things is short. Leave it unstarted, with your ignition off too. The attendants at the forecourt — whether at Shell itself or wherever you filled up — will usually help push it clear of the petrol pump if you ask. Next, 0333 366 0103. We will ask what was put in, roughly how much, and if it has been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a different issue — Dulwich has a page all for it.
One petrol in a diesel job in Dulwich costs more than another. Why?
The four situations above are four separate tasks, so no single quote for this would be honest. Which of them you are in is chiefly what moves your cost. Where the vehicle is matters too, and whether a technician can safely reach it, after the proportion of petrol to what your tank takes.
That's why we ask three queries before costing instead of after: what went in, how much, and if it has run. Those replies are what turn a range into one firm number.
About Dulwich
Dulwich is a suburban area in south London, situated approximately 5.4 miles from the city centre. Dulwich has a relatively low elevation of 61 metres and is close to nearby places such as Sydenham Hill, West Dulwich, and Gipsy Hill. Dulwich is predominantly composed of flat housing and has a population of around 3672 residents. Dulwich is also near Westminster, which is about 4.9 miles away.
Fuel drain cover around Dulwich and across Greater London
Petrol in diesel calls in Dulwich — part of the SE postcode area — go to vans that also cover the places round it, Sydenham Hill, West Dulwich and Gipsy Hill included. The vehicle doesn't need to move to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Still at the pump in Dulwich?
The best place there is, then — that is where you are. Call, and keep it switched off.