Petrol in a Diesel Car in Mountain Air: How Worried Should You Be?
Likely less than you are now — as long as no one has started the car. Everyone around Mountain Air starts with "have I ruined it?", and the fair answer is normally no: petrol left in the tank of a diesel stays harmless until priming, cranking or driving draws it into the fuel system. To leave the car like that, phone Petrol in Diesel and leave your engine switched off. Below, this page sets out what petrol really does inside a diesel, how far it may have got, and how to stop it happening to you again.
Petrol in a diesel: what does it do to the motor?
Two tasks fall to diesel on its route through a motor. It ignites, and before it ignites it protects. Your high-pressure pump and the fuel injectors are made to very fine clearances, and your diesel passing through them is what stops those surfaces from wearing against each other.
Petrol does the first job badly and the second not at all. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, so a pump on the mixture to wear itself. It's also made to resist igniting under compression — the opposite of what a diesel needs — which is why you get the rattling.
Taken together, they show what shape the problem takes. Not contact but circulation is what does the harm. All a tank with petrol in it amounts to is a fuel problem. Whatever a worn pump sheds goes on, carried by your fuel, into the fuel injectors further along, which is why a pump that has worked on the petrol is where a mechanical issue starts.
Petrol in a diesel in Mountain Air: how bad is it? Four situations
Filled but never started — as good as it gets. Being on a forecourt is what makes this possible: elsewhere, your car has been driven there to begin with. With the petrol kept inside the tank alone, it is drained and purged on the spot, and nothing more is needed.
Started for a moment, or just the ignition on. Once primed, the system has drawn petrol from the tank as far as the filter and the lines. That is usually still an easy job — a drain, a flush, and the fuel filter seen to.
Those few miles driven were the pump working on fuel diluted by petrol the whole way. Tank, lines, filter, then clean fuel put through the whole circuit: that is this work, and the way the vehicle was driven counts as much as the distance. Driving the kids to the local primary school is one kind of trip. Very different once more: a run to Newport, under 25 miles away, or some mileage on the M4, under 25 miles from Mountain Air, where your engine kept working hard.
Knocking, an uneven idle, smoke, a throttle gone soft: driven until it complained. The motor is telling you your fuel is no longer behaving like diesel. Leave it where it has stopped: a lay-by, a quiet street, the verge on Pen-y-Parc. A vehicle stopped quickly very rarely has long-term damage, because the drain and the flush, which still come first, sort it out.
What Mountain Air motorists get told about petrol in a diesel — and the myths in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." A bigger tank of the same mix is all it gives, since topping up takes out nothing. That guidance supposes a diesel fuel system tolerates petrol by percentage. It doesn't.
If anything, the opposite holds. Myth: "A modern diesel can cope with a bit of petrol." At higher pressure, through smaller components: that is how a current diesel moves its fuel, and so the lubrication matters for more, not less.
"It starts, it drives, and so no harm done" — the myth that catches more people than any other. Diesel in a petrol motor generally means a motor that will not run: the motorist stops, and so does the harm. A diesel fed petrol generally starts, idles and drives away as though nothing has happened, while the pump grinds. Fine and running aren't the same thing.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an outdated fix for a distinct fault. None of what petrol thinned gets put back by it — and afterwards, the tank still contains that petrol.
"Drain it yourself and you are sorted" — a myth, because after it has been running some petrol lies in your filter and lines, ready to go right back through the pump at your next start. Draining petrol into a can by the kerbside is also genuinely risky.
Why petrol in a diesel happens at all
On purpose? Never. Through carelessness? Seldom, if ever. A diesel nozzle mostly will not go into a petrol car, but the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake simple, and only in that direction.
Habit and your car getting out of step is how it occurs. Hire cars, courtesy cars, and cars that are new to you. A household with one petrol and one diesel on the driveway. A familiar forecourt with the pumps in a different order. A train to catch, and a hurried fill on the way to Ebbw Vale Town. The first fill-up in a diesel Renault Megane after years of driving petrol is precisely the moment it takes place. Throw in rain, a phone call or a back seat full of children, and your hand does what it has always done.
Avoiding petrol in a diesel next time you fill up in Mountain Air
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most usually do. Read the pump's label; the colour is only a clue.
- In a car you don't know, look inside the flap over your filler or at the cap before the first fill: plenty of cars print the fuel there.
- One of each in the home? Label the key to the diesel — a bright fob, a sticker — since intending to remember is not enough.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the petrol pump. It seems daft and it works.
- Mistakes like this are straightforward to make whilst your mind is on something else, so your phone goes away.
- Add-on devices are available for vehicles without one, and some diesels are built with a filler that won't accept a petrol nozzle. Useful — but a backstop at best, never a reason to stop checking the label.
- Spotting it halfway? Stop there and then. A weaker blend results from less petrol inside that tank, but your next stage stays the same: don't start the vehicle.
Mountain Air: already put petrol in a diesel?
Then, there's only a short order of things. Don't switch your ignition on, and don't start it. Ask the attendants to help you push it clear of the pump if you are still on the forecourt, whether that is Tesco or anywhere else. Then call 0333 366 0103 and tell us what went in, about how much, and if it has run.
Corrosion and deposits are the issue with AdBlue, whereas petrol brings lost lubrication. So if it was AdBlue, say so — and read its own Mountain Air page.
Why one petrol in a diesel task around Mountain Air costs more than another
Four different tasks lie behind the four scenarios above — which is why there is no fair single quote. Mostly, the cost moves with which one you're in. Two things come after that: the petrol that got in as a proportion of what the tank holds, then the spot the vehicle is in and whether our van can reach it safely.
What got in, how much, and whether it has run — three queries our technicians ask before quoting, not after, for exactly that reason. Those answers change a range into a straight figure.
About Mountain Air and its setting
Mountain Air is a suburban area situated in the county of Blaenau Gwent, within the wider Welsh valleys region. Mountain Air sits at an elevation of 363 metres, overlooking the surrounding landscape. Mountain Air is characterised by its predominantly terraced housing stock, reflecting the area's historical development as a residential community. Mountain Air is located near other local places such as Hilltop, Willowtown, and Ebbw Vale, and is approximately 16.5 miles from the city of Newport.
Across Blaenau Gwent and around Mountain Air: fuel drain cover
Hilltop, Willowtown and Ebbw Vale are among the places around Mountain Air that the same vans work, answering petrol in diesel call-outs across Mountain Air's NP postcode area. The car doesn't need to move to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
At the petrol pump in Mountain Air, right now?
Then you are in the best spot there can be. Keep it off. Ring.