Welling: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less anxious than you probably feel. Until your ignition primes the pump, your starter cranks, or your car is driven, petrol in a diesel tank simply waits there and does no harm. Which makes the honest reply to that first Welling question — "have I wrecked it?" — usually no. To keep it that way, phone Petrol in Diesel and leave the engine alone. The remainder of this page explains what petrol actually does to a diesel, how to tell how far it has got, and how to make sure it doesn't happen to you again.
The engine and petrol in a diesel: what happens
Diesel has two tasks on its way through a motor. It ignites, and before it combusts it protects. Very fine gaps are built into the fuel injectors and the high-pressure pump, and only your diesel flowing through keeps those surfaces from grinding together.
Petrol handles the first job badly and the second not at all. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump running on that mixture wearing itself. It is also made to resist igniting under compression — the opposite of what a diesel needs — which is where you get the rattling.
Put these together and the shape of the problem is clear. Not contact but circulation is what does the damage. All a tank with petrol in it amounts to is a fuel fault. Once the pump has been running on that petrol, a mechanical fault has begun: whatever is shed by a pump that's wearing down is carried onward to your injectors with the fuel.
Four scenarios we see in Welling: how serious is petrol in a diesel?
Filled up, never started. The best case there can be. That petrol is inside that tank and just that tank, and the job is a drain and a flush where the car sits. This is the one scenario that can only really happen at a forecourt, as anywhere else your car has been driven to get there.
The ignition turned on, or a brief start. The fuel system has been primed, so petrol has left your tank and reached your filter and the fuel lines. Drain, flush, deal with your filter: still normally straightforward.
Those few miles driven were the pump running 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 your car was driven counts as much as the mileage. Short trips, such as the school run to St Stephen's Catholic Primary School, are one matter. A run as far as London, under 10 miles away, is a very different job. So is any miles on the M25, under 10 miles from Welling, where the engine has been labouring hard the whole time.
Driven on till it complained — rattling, smoke, an uneven idle, a soft throttle. What you are hearing is your motor reporting fuel that no longer runs like diesel. Leave it where it stops: a lay-by, a side street, the verge on Hook Lane. Lasting damage is very uncommon if a car is pulled over early, and the fuel drain and flush that still go first sort it out.
What Welling motorists get told about petrol in a diesel — and the myths in it
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. Nothing comes out when you top up — your tank simply holds more of the same blend. Percentage isn't how a diesel fuel system copes with petrol, whatever that advice assumes.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the opposite. More precise parts and higher pressure are the way a modern diesel runs its fuel, and that makes the lubrication matter more, not less.
This is the one that fools drivers. Myth: "If it starts and drives, there is no harm done." Feed diesel to a petrol motor and it normally will not run, and so the motorist stops — and the damage stops with them. Feed petrol to a diesel and it normally fires up, ticks over and drives away as if nothing has happened — all the while its pump wears. Being able to run is not the same as being fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a different problem. The petrol is still inside your tank afterwards, and what it has weakened isn't put back.
The next start sends petrol back round the pump out of your lines and the filter, where some of that ends up after the engine has been run. That's why draining the tank yourself does not leave you sorted — a myth. Also, a can of petrol filled at the kerbside is genuinely hazardous.
Petrol in a diesel: how does it occur?
Nobody does it on purpose, and it is seldom carelessness. The petrol nozzle is the slimmer of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol motor at all. The forecourt makes it simple, and the mistake runs one way.
Habit and the car getting out of step is how it takes place. Hire cars, courtesy cars, and cars that are new to you. Two motors on one driveway, one petrol, one diesel. A well-known forecourt with the pumps in a different order. A train to catch, and a hurried fill en route to the nearest station. Years of petrol cars behind you, a diesel Volkswagen Tiguan in front of you at the forecourt for its first tank — that's when. The hand does what it has always done once you add rain, a phone call or a back seat full of kids.
Welling motorists: how to avoid petrol in a diesel next time
- Read the petrol pump, not the colour. In the UK unleaded handles are generally green and diesel black, yet not on each forecourt. The label is what matters.
- Check your filler flap. Plenty of cars state the fuel type inside the flap or on the cap. Look at it on your first fill in any motor you don't know.
- One of each in the home? Mark your key to your diesel — a coloured fob, a sticker — since intending to remember is not enough.
- "Diesel", aloud, before you pick up the nozzle — each time a new or hired car needs its first tank. It sounds silly. It does the trick.
- Thinking about something else is when this becomes an easy mistake to make, and so tuck your phone away and keep your mind on the pump.
- Some diesels have a filler designed to reject a petrol nozzle, and devices you can add exist for motors without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the petrol pump.
- Less petrol means a weaker mix, so stop the moment you realise — though remembering that the next stage is unchanged. It's still not to fire it up.
Welling: already put petrol in a diesel?
The order of things is brief, then. Starting it is out, and so is switching on your ignition. The staff 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. Next, 0333 366 0103. We'll ask what was put in, about how much, and if it's been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a separate fault — Welling has a page just for it.
One petrol in a diesel job around Welling costs more than another. Why?
There's no honest single price for this, because the four situations above are four separate jobs. What moves your cost is mostly which of them you are in. The proportion counts next, meaning how much of your tank is petrol, followed by the position of your car and whether getting to it is safe for a van.
That's why our engineers ask three questions before quoting rather than after: what got in, how much, and whether it has run. Those replies are what turn a range into one firm number.
About Welling
Welling is a suburban area in southeast London, situated on the banks of the River Thames at an elevation of around 47 metres. Welling lies approximately 10 miles from central London and is surrounded by other suburban areas, including East Wickham, Falconwood, and Blackfen. Welling has a population of around 10,739 people and is characterised by its predominantly semi-detached housing stock. Welling is connected to London by road and rail links, making it a commuter-friendly location.
Across Greater London and in Welling: fuel drain cover
Our teams answering petrol in diesel jobs around Welling, in the DA postcode area, equally work the spots near it, East Wickham, Falconwood and Blackfen among them. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations we drain, and your vehicle does not need to move to us.
In Welling and still at the petrol pump?
The best place there is, then — that is where you are. Keep it off. Phone.