Cogan: Petrol in a Diesel Car? How Worried to Be
Probably less than you are now — provided nobody has started it. Petrol resting in a diesel tank does nothing to your engine till something pulls it through the fuel system — your ignition priming the pump, your starter, or the drive on its own. So the truthful answer to the first query everyone around Cogan asks, "have I wrecked it?", is generally no. To leave the car that way, call Petrol in Diesel then leave the motor switched off. What petrol really does to a diesel, how to gauge how far it's gone, and how to stop it from happening a second time: that's the remainder of this page.
What petrol in a diesel does to the engine
On its way through an engine, diesel has two tasks. It lubricates to begin with, and after that does it burn. Extremely fine gaps are built into the injectors and your high-pressure pump, and only your diesel flowing through stops those surfaces grinding together.
Badly at the first, not at all at the second: that is petrol. The rattling comes from petrol being made not to ignite when compressed, which is exactly the reverse of what a diesel needs. On top of that it is thinner than diesel, it strips away the protection the fuel system rests on, and any pump running on such a blend is wearing itself.
Put those together and the shape of the trouble is plain. It is movement that causes the damage, not contact. All a tank with petrol in it amounts to is a fuel issue. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the injectors further on.
Four situations our engineers see in Cogan: how serious is petrol in a diesel?
Filled up, not once started. The best case there is. On a forecourt, and genuinely only there, the petrol is still limited to your tank — because anywhere else the car was driven to get to it. The job is emptying and flushing on the spot.
Ignition on, or started for a moment. Your system has been primed, and so petrol has left that tank and reached your filter and your lines. That's usually still a straightforward task — a drain, a flush, and the filter dealt with.
Driven a couple of miles. Now your pump has spent those miles working on thinned fuel. Tank, lines, filter, then clean fuel put through the whole system: that is this work, and the way the car was driven counts as much as the distance. Driving the kids to the local primary school is one sort of trip. Getting as far as Cardiff, under 3 miles away, makes a very different job — as does any distance on the M4, under 10 miles from Cogan, with the motor working hard the whole time.
Driven until it complained. Rattling, a ragged idle, smoke, a throttle that has gone soft. That is your engine telling you its fuel has stopped acting like diesel. Leave it where it has stopped: a lay-by, a side street, the verge on Foxglove Rise. A car pulled over early very rarely has permanent damage, since the fuel drain and the flush, which still go first, take care of it.
Petrol in a diesel stories Cogan drivers hear
Myth: topping up to full with diesel makes it fine. It doesn't. Nothing comes out when you top up — the tank simply holds more of the same mixture. The assumption behind that advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: a modern diesel copes with a bit of petrol. Rather, the reverse. Protection counts more on modern diesels, not less, since their fuel passes through finer parts at higher pressure.
This is the one that catches drivers. Myth: "If it starts and drives, there is no harm done." The motorist of a petrol engine fed diesel normally stops, since it will not run, and the harm stops with them. Feed petrol to a diesel and it generally starts, idles and drives away as if nothing happened — all the while its pump is wearing. Being able to run is not proof of being fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a separate fault. The petrol is still in your tank afterwards, and whatever it has thinned isn't put back.
"Drain it yourself and you're sorted" — a myth, because after it has been running some petrol sits in the fuel filter and lines, ready to go right back through the pump on the next start. And, a can of petrol drained by the roadside is genuinely risky.
How it happens: petrol in a diesel
It's seldom carelessness, and no one does it on purpose. A diesel nozzle mostly won't fit a petrol vehicle, yet the narrower petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one error easy, and just in that direction.
The moment habit stops matching the car is the moment it takes place. Hire cars, courtesy cars, and cars that are new to you. Households running one of each, petrol and diesel. A forecourt you know, only with its pumps laid out differently. Fuelling up in a hurry on the way to the nearest station, with a train to catch. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is exactly the moment it happens. Throw in rain, a phone call or a back seat full of children, and the hand does what it has always done.
Cogan people: how to prevent petrol in a diesel next time
- Check the petrol pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on every forecourt. The label is what counts.
- The first fill in a new car is the time to check your filler flap — on it, or on the cap, many motors state which fuel to use.
- Good intentions do less than a sticker or a fob in a bright colour on your diesel's key if a home has one of each. So label it.
- "Diesel", aloud, before you lift the nozzle — each time a new or hired car gets its first tank. It seems daft. It works.
- Tuck the phone away. This is an easy mistake to make while you are thinking about something else.
- Some diesels come with a filler designed to reject a petrol nozzle, and devices you can add are available for motors without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop checking the pump.
- Spotting it mid-fill? Stop there and then. A thinner mix results from less petrol in the tank, but your next step stays the same: do not fire it up.
Already put petrol in a diesel in Cogan?
Then the order of things is short. Starting it is out, and so is switching on your ignition. Ask the attendants to help you push it away from the petrol pump if you're still at the forecourt, whether that is Tesco or anywhere else. What went in, roughly how much, and if it has run: tell us that when you call 0333 366 0103.
Say so if it was AdBlue rather than petrol: it is a separate issue, with its own page for Cogan, since AdBlue brings corrosion and deposits instead of lost lubrication.
Why one petrol in a diesel job in Cogan costs more than another
Four separate tasks sit behind the four situations above — which is why there's no honest single quote. Mostly, your cost moves with which one you are in. The ratio matters next, meaning how much of that tank is petrol, and then the position of the car and whether reaching it is safe for our van.
What went in, how much, and whether it's run — three queries our technicians ask before costing, not after, for precisely that reason. Those answers are what change a range into one firm number.
About Cogan itself
Cogan is a suburban area in the Vale of Glamorgan, situated near the coast and approximately 2.8 miles from Cardiff. Cogan has a relatively low elevation of 38 metres and is characterised by semi-detached housing. Cogan is part of the wider Cardiff urban area, with nearby places including Llandough, Morristown, and Murch.
Fuel drain cover across The Vale of Glamorgan, Cogan included
Our teams answering petrol in diesel jobs in Cogan, in the CF postcode area, also work the spots around it, Llandough, Morristown and Murch included. You need not bring the vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all locations where we work.
At the petrol pump around Cogan, still?
In that case, you could not be in a better place. Phone, and leave it turned off.