Derwen: Petrol in a Diesel Car? How Worried to Be
If it hasn't been started, you can worry less than you probably are. "Have I ruined it?" is the first thing everyone around Derwen asks, and the truthful answer is generally no, because petrol resting in a diesel tank hurts nothing till it's drawn through your fuel system — by ignition priming, by the starter, or by being driven. Petrol in Diesel is who to phone, with the motor left off, and so it remains that way. What petrol actually does to a diesel, how to gauge how far it has travelled, and how to stop it from happening a second time: that's the rest of this page.
What petrol in a diesel does to the motor
Two jobs fall to diesel on its journey through a motor. It lubricates to begin with, and after that does it burn. The high-pressure fuel pump and your injectors are designed to extremely fine gaps, and the diesel passing through them is what stops those surfaces from grinding against one another.
The second job petrol does not do at all, and the first it does badly. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump on the mixture wearing itself. It is also made to resist igniting under compression — the opposite of what a diesel needs — which is where you hear the clattering.
Seen together, they make clear the shape the issue takes. The damage is done by circulation, not by contact. Where the petrol is only inside your tank, it's a problem of fuel, nothing more. Once your pump has been labouring on that petrol, a mechanical fault has started: whatever is shed by a pump that is wearing is carried downstream to your injectors with the fuel.
Derwen, petrol in a diesel: four cases, from mild to serious
Filled up, not once started. The best case there is. That petrol is in that tank and only that tank, and the task is a drain and a flush where the car stands. This is the one situation that can only really happen at a forecourt, as anywhere else your car has been driven to get there.
Started for a second, or only the ignition on. With the system primed, your lines and filter already contain petrol that came from the tank. Drain, flush, deal with your filter: still usually straightforward.
Driven a few miles. Now your pump has spent those miles running on weakened fuel. Tank, lines, filter, then clean fuel put through the entire system: that is this work, and the way the car was driven counts as much as the miles. Driving the kids to the local primary school is one sort of trip. Very different again: a trip to Swansea, under 25 miles away, or any mileage on the M4, under a mile from Derwen, where your engine never stopped running hard.
Driven on till it protested — rattling, smoke, an uneven idle, a soft throttle. The engine is telling you your fuel is no longer acting like diesel. Stop wherever you are — the verge on Heol Hopcyn John, a lay-by, a side street — then leave the vehicle there. A vehicle pulled over early very rarely has lasting damage, because the fuel drain and the flush-through, which still go first, deal with it.
What Derwen drivers get told about petrol in a diesel — and the stories in it
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Topping up takes out nothing; it gives you a fuller tank of the same mixture. The idea behind that guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: a current diesel copes with a bit of petrol. Rather, the opposite. Lubrication counts more on newer diesels, not less, because their fuel passes through smaller parts at higher pressure.
This is the one that fools people. Myth: "If it starts and drives, there is no damage done." Feed diesel to a petrol engine and it normally will not run, and so the motorist stops — and the damage stops with them. While the pump wears, a diesel fed petrol usually starts, idles and drives away as if nothing has happened. A running engine does not mean fine.
Not so: a two-stroke additive makes it safe to drive home. It was an old fix, meant for another fault. None of what petrol diluted is put back by it — and afterwards, that tank still contains that petrol.
If the motor has been run, part of the petrol is in the filter and the lines, not that tank — and the next start pulls it straight back through the pump. So the myth "drain the tank yourself and you're sorted" doesn't hold. And, a can of petrol drained at the roadside is genuinely risky.
How does petrol in a diesel happen?
It's seldom carelessness, and no one does it on purpose. The petrol nozzle is the smaller of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol vehicle at all. The forecourt makes it simple, and the slip runs one way.
When routine and the vehicle stop matching, it occurs. A new vehicle, a hire car or a courtesy car. Two cars on one driveway, one petrol, one diesel. Your normal forecourt, its pumps now in a different order. A train to catch, and a hurried fill en route to Wildmill. A new-to-you diesel Volkswagen Passat, its first fuelling, and a driver accustomed to petrol: exactly when it occurs. Add a back seat full of kids, a phone call or rain, and the hand takes over.
Next time you fill up around Derwen: avoiding petrol in a diesel
- The label is what counts, and so check the pump instead of the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt.
- In a motor you do not know, look inside the flap over the filler or at the cap before your first fill: plenty of motors state the fuel type there.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of intending to remember, for a home with one of each.
- "Diesel", aloud, before you lift the nozzle — each time a new or hired car gets its first tank. It seems daft. It works.
- Mistakes like this are simple to make whilst your mind is on something else, and so the phone goes away.
- Some diesels have a filler built to block a petrol nozzle, and devices you can add exist for cars without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the pump.
- Less petrol makes a thinner mixture, and so stop as soon as you realise — though remembering that your next step is unchanged. It is still not to start it.
Already put petrol in a diesel in Derwen?
Short and simple, then, is the order of things. Don't crank it, and do not turn your ignition on. Ask the attendants to help you roll it clear of the pump if you're still on the forecourt, whether that is Sainsbury's or anywhere else. Phone 0333 366 0103 next, with three answers — your fuel, the rough amount, and if it's run.
Corrosion and deposits are the problem with AdBlue, where petrol means lost protection. So if it was AdBlue, say so — and read its own Derwen page.
Derwen petrol in a diesel tasks: why one costs more than another
There is no honest single price for this, because the four scenarios above are four separate jobs. Which of them you are in is chiefly what shifts your cost. Where the car is counts too, and whether our van can safely get to it, after the proportion of petrol to what the tank takes.
Ahead of any quote, not after, come three queries: your fuel that was put in, its volume, and whether it's run. That's why. Their answers are what change a range into one firm number.
About Derwen
Derwen is a small hamlet in Bridgend, situated inland at an elevation of 91 metres, with Detached housing being the predominant type of accommodation. Derwen lies near several nearby places, including Litchard, Pen-y-cae, and Pen-yr-heol, and is approximately 17 miles from the city of Swansea. Derwen is characterized by its rural setting and relatively small population of around 2799 residents. Derwen is also located a significant distance from London, at around 148 miles away.
Derwen and Bridgend: where our fuel drain cover runs
Petrol in diesel calls around Derwen — part of the CF postcode area — go to vans that also cover the spots round it, Litchard, Pen-y-cae and Pen-yr-heol among them. The car does not need to come to us: our engineers drain on a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
At the petrol pump around Derwen, right now?
No position is better: that is where you are. Turned off it stays; then ring.