Oldfield: Petrol in a Diesel Car? How Worried to Be
Provided it has not been started, worry far less than you likely are. Until the ignition primes your pump, the starter cranks, or the car is driven, petrol in a diesel tank just sits there and does nothing. Which makes the honest reply to the first Oldfield question — "have I ruined it?" — usually no. Keep it like that: leave the motor off then phone Petrol in Diesel. Keep reading for three things: the effect petrol has inside a diesel motor, the signs of how far it has spread, and ways to make sure you don't do it again.
Petrol in a diesel: what does it do to the engine?
On its way through an engine, diesel does two tasks. It combusts, and before it burns it protects. The high-pressure pump and your injectors are made to extremely fine gaps, and your diesel passing through them is what keeps those surfaces from wearing against each other.
Petrol does the first job badly and the second not at all. A pump running on a petrol mixture is wearing itself out, because petrol is thinner than diesel and strips out the protection the fuel system depends on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that is where any rattling comes.
The shape of the problem is clear once you put those together. The damage is done by movement, not by contact. All a tank with petrol in it amounts to is a fuel issue. Once the pump has been working on that petrol, a mechanical fault has started: anything shed by a pump that is wearing down travels downstream to the fuel injectors with your fuel.
Four scenarios we see around Oldfield: how serious is petrol in a diesel?
Fuelled but never started — the best it gets. The petrol is in the 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 take place on a forecourt, because anywhere else your car has been driven to get there.
Ignition on, or started for a second. Once primed, the system has pulled petrol from that tank up to the filter and the fuel lines. Still generally easy: drain, flush, and the filter dealt with.
A couple of miles driven, and your pump has spent each of them working on diluted fuel. Tank, lines, filter, then clean fuel put through the entire circuit: that's the work, and the way your car was driven matters as much as the distance. On the school run to Morville CofE (Controlled) Primary School, the miles is small. Any mileage on the M54, under 15 miles from Oldfield, means the engine has worked hard throughout, and a run to Wolverhampton, under 25 miles away, makes a very different task too.
Driven on until it complained — clattering, smoke, a ragged idle, a soft throttle. What you are hearing is your engine reporting fuel that no longer runs like diesel. Leave it wherever it has stopped: a lay-by, a quiet street, the verge on B4364. The drain and flush-through still go first, and they sort it out: when a car is pulled over quickly, lasting damage is very unusual.
Oldfield people and that petrol in a diesel stories they hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. Topping up removes nothing; it gives you a fuller tank of the same mixture. A diesel fuel system doesn't tolerate petrol by percentage in the way that guidance supposes.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the reverse. More precise parts and higher pressure are the way a modern diesel runs its fuel, and that makes the protection matter more, not less.
This is the one that catches people. Myth: "If it starts and drives, there is no harm done." Feed diesel to a petrol engine and it generally will not run, so the driver stops — and the harm stops with them. Whilst the pump wears, a diesel fed petrol usually starts, idles and drives away as if nothing has happened. Being able to run is not the same as being fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a distinct problem. The petrol is still in your tank after that, and what it has weakened is not put back.
Once your engine has been run, part of the petrol sits in the filter and the fuel lines, not the tank — and the next start sends it right back through the pump. So the myth "drain the tank yourself and you are sorted" doesn't stand up. It's also really risky to drain petrol into a can by the roadside.
How does petrol in a diesel happen?
It is seldom carelessness, and nobody does it on purpose. One way only, since of the nozzles: the narrower petrol one slips inside a diesel filler with almost no resistance, whereas the diesel one generally will not fit a petrol car. That's how the forecourt makes it straightforward.
The moment routine stops matching the vehicle is the moment it occurs. Hire cars, courtesy cars, and vehicles that are new to you. A household with one petrol and one diesel on the driveway. The pumps in a different order on a familiar forecourt. Filling up in a rush en route to the nearest station, with a train to catch. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist accustomed to petrol: exactly when it happens. With rain, a call arriving, or a car full of children to deal with, your hand just does what it has always done.
Preventing petrol in a diesel next time you fill up around Oldfield
- Read the pump, not the colour. In the UK unleaded handles are generally green and diesel black, but not on every forecourt. The label is what matters.
- Plenty of cars state the fuel type inside your filler flap or on the cap, and so check there on your first fill in a car you don't know.
- Good intentions count for less than a sticker or a fob in a vivid colour on the diesel's key when a home has one of each. So mark it.
- Say it before you lift it. On your 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.
- Tuck your phone away. This is an easy mistake to make while you are thinking about something else.
- Some diesels come with a filler built to block a petrol nozzle, and devices you can add exist for vehicles without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop checking the pump.
- Stop as soon as you notice. Less petrol inside your tank makes a weaker mix. It does not change what to do next, which is still not to fire it up.
Already put petrol in a diesel in Oldfield?
Short and simple, then, is the order of things. Leave it unstarted, with your ignition off as well. If you're still at the forecourt — the nearest petrol station or anywhere else — ask the attendants to help you roll the car away from the petrol pump. Call 0333 366 0103 next, with three facts — the fuel, the approximate quantity, and whether it has run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a different problem — Oldfield has a page just for it.
Why one petrol in a diesel task in Oldfield costs more than another
The four situations above are four separate tasks, so no single price for this would be honest. What moves your cost is mostly which of them you're in. Two things follow that: the petrol that went in as a proportion of what that tank takes, then the place the car is in and whether a van can reach it safely.
What was put in, how much, and if it's run — three queries our engineers ask before costing, not after, for precisely that reason. With those replies, you get a straight figure rather than a range.
About Oldfield itself
Oldfield is a small hamlet in Shropshire, situated inland at an elevation of 193 metres, and is located approximately 16 miles from Wolverhampton. Oldfield comprises predominantly detached housing and has a population of around 579 residents. Oldfield is part of a wider rural area that includes nearby places such as Eudon George and Middleton Scriven. Oldfield sits within the West Midlands region, about 121 miles northwest of London.
Oldfield and Shropshire: where our fuel drain cover reaches
Oldfield sits in the WV postcode area, and our teams that answer petrol in diesel jobs there work the locations near it as well — Eudon George, Middleton Scriven and Defford among them. Our engineers drain wherever the vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
At the pump around Oldfield, still?
In that case, you couldn't be in a better position. Leave the car switched off, and ring.