How Worried Should You Be? Petrol in a Diesel Car in Johnston
Likely less than you are now — as long as nobody has started it. Everyone around Johnston starts with "have I ruined it?", and the honest answer is generally no: petrol resting inside your tank of any diesel remains harmless till priming, cranking or driving draws it into the system. To keep the vehicle that way, call Petrol in Diesel and leave the motor switched off. The remainder of this page covers what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it does not happen to you again.
What petrol in a diesel does to the motor
Diesel has two jobs on its way through a motor. Before it ignites, it lubricates — then it combusts. Your high-pressure pump and the fuel injectors are built to very fine tolerances, and your diesel passing through them is what stops those surfaces from grinding against each other.
Petrol handles the first task badly and the second not at all. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump running on that mixture to wear itself. It's equally made to resist igniting under compression — the opposite of what a diesel needs — which is why you get the rattling.
The shape of the trouble is clear when you put those together. It is movement that causes the damage, not contact. Where the petrol is only in the tank, it is an issue of fuel, nothing more. The beginning of a mechanical problem is a pump that has been working on that petrol — and whatever a worn pump sheds moves on with your fuel to your injectors beyond it.
Johnston, petrol in a diesel: four cases, from mild to serious
Filled up, never started. The best case there can be. The petrol is inside your tank and only your tank, and the task is a drain and a flush where the vehicle stands. This is the one situation that can only really happen on a forecourt, because anywhere else your car has been driven to get there.
Ignition on, or started for a moment. With the fuel system primed, the lines and filter already contain petrol that has come from your tank. Still normally straightforward: drain, flush, and your filter dealt with.
Those few miles on the road meant your pump running on fuel diluted by petrol throughout. Tank, lines, filter, then clean fuel put through the entire circuit: that is this work, and the way the car was driven matters as much as the miles. Driving the children to the local primary school is one sort of trip. Very different a second time: a run to St Davids, under 15 miles away, or any miles on the M4, under 50 miles from Johnston, where the motor kept running hard.
Driven till it protested. Clattering, an uneven idle, smoke, a throttle that has gone soft. That is your motor telling you its fuel no longer is acting like diesel. Whether it's the verge on St. Peter's Road, a lay-by or a side street, stop there then leave it. Permanent damage is very uncommon if a vehicle is stopped early, and the fuel drain and flush-through that still come first sort it out.
Myths Johnston motorists hear about petrol in a diesel
"Top it up the rest of the way with diesel and it will be fine" — a myth. It will not. A fuller tank of the same mix is all you get, because topping up takes out nothing. A diesel fuel system does not tolerate petrol by percentage in the way that guidance assumes.
Not so: a modern diesel copes with a bit of petrol. If anything, the opposite. A modern diesel runs its fuel through finer components at higher pressure, which makes the protection count more, not less.
Myth: "If it starts and drives, there's no damage done." This is the one that fools drivers. Any petrol engine fed diesel usually won't run, so the motorist stops and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile your pump wears. Being able to run is not proof of being fine.
An outdated fix for a different fault is behind this one. Myth: "Add some two-stroke oil and drive the car home." It does not put back what petrol has diluted, and the petrol is still in that tank later.
If the engine has been run, part of that petrol sits in the filter and the lines, not your tank — and your next start sends it straight back through your pump. So the myth "drain your tank yourself and you're sorted" does not stand up. It's also really risky to drain petrol into a can by the roadside.
Petrol in a diesel: how does it occur?
No one does it on purpose, and it is seldom carelessness. A diesel nozzle generally won't go into a petrol car, but the narrower petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake simple, and just in one direction.
The moment routine stops matching the car is the moment it happens. Hire cars, courtesy cars, and cars that are new to you. Households running one of each, petrol and diesel. The pumps in a different order on a well-known forecourt. A train to catch, and a hurried fill on the way to the nearest station. Precisely the moment it happens: after years of driving petrol, a driver fills a diesel Volkswagen Golf for the first time. The hand repeats what it has always done when you add rain, a phone call or a back seat full of children.
Johnston people: how to prevent petrol in a diesel next time
- The label is what counts, and so read the pump rather than the colour: in the UK unleaded handles are usually green and diesel black, yet not on each forecourt.
- The first fill in a strange motor is the time to check your filler flap — on it, or on the cap, many motors state which fuel to use.
- A coloured fob or a sticker on the diesel's key does more than any amount of intending to remember, in a house with one of each.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the pump. It sounds daft and it does the trick.
- Tuck the phone away. This is an easy mistake to make while you are thinking about something else.
- Add-on devices exist for vehicles without one, and some diesels come with a filler that will not take a petrol nozzle. Helpful — but a backstop at best, never a reason to stop checking the label.
- Stop as soon as you notice. Less petrol inside the tank makes a thinner mixture. It doesn't change what to do next, which is still not to fire it up.
Petrol already in a diesel in Johnston? Begin here
Then the order of things is short. Never start it, and do not switch the ignition on. Ask the attendants to help you roll it clear of the petrol pump if you're still at the forecourt, whether that's BP or anywhere else. What was put in, about how much, and if it's run: tell us those when you ring 0333 366 0103.
Say so if it was AdBlue rather than petrol: it is a different issue, with its own page for Johnston, since AdBlue brings corrosion and deposits rather than lost lubrication.
What makes one Johnston petrol in a diesel job cost more than the next
There's no fair single price for this, because the four scenarios above are four different jobs. The situation itself does most of the work of moving your cost. Where the car is counts too, and whether a technician can safely get to it, after the proportion of petrol to what the tank takes.
Three queries come first, before quoting, instead of after — what went in, how much, has it run — and that is the reason. Those replies change a range into a straight figure.
About Johnston
Johnston is a village in Pembrokeshire, situated inland at an elevation of 74 metres, and is located near the communities of Pope Hill, Clareston, and Freystrop. Johnston has a population of approximately 1614 people, and its housing stock is predominantly semi-detached. Johnston sits about 14 miles from St Davids, the smallest city in the UK, and is around 209 miles from London.
Fuel drain cover around Johnston and across Pembrokeshire
Our teams answering petrol in diesel jobs around Johnston, in the SA postcode area, also work the spots near it, Pope Hill, Clareston and Freystrop among them. The car does not need to come to us: our technicians drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
In Johnston and still at the petrol pump?
Then you are in the best spot there is. Phone, and keep it turned off.