Petrol in a Diesel Car in Pen-y-Darren: How Worried Should You Be?
Probably less than you already are — as long as no one has started it. Petrol resting in a diesel tank does nothing to the motor till something draws it through your fuel system — the ignition priming the pump, the starter, or driving on its own. So the fair answer to the first question everyone around Pen-y-Darren asks, "have I wrecked it?", is normally no. To leave the car like that, phone Petrol in Diesel and leave your motor alone. What petrol actually does to a diesel, how to judge how far it's gone, and how to stop it from happening a second time: that's the rest of this page.
Your engine and petrol in a diesel: what happens
Two jobs fall to diesel on its journey round a motor. It combusts, and before it ignites it lubricates. Very fine tolerances are built into the injectors and your high-pressure pump, and only your diesel flowing through stops their surfaces grinding together.
Of those two jobs, petrol handles the first badly and the second never. A pump working on a petrol mix is wearing itself out, because petrol is thinner than diesel and takes away the lubrication your fuel system relies on. Petrol is also made to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that's where any knocking comes.
The shape of the trouble is plain once you put those together. It is circulation that does the harm, not contact. All a tank with petrol in it amounts to is a fuel problem. Whatever a worn pump sheds travels on, borne by your fuel, into your injectors further along, which is why a pump that has worked on that petrol is where a mechanical fault begins.
Four situations our technicians see around Pen-y-Darren: how bad is petrol in a diesel?
Filled up, and never started: nothing beats it. Being at a forecourt is what makes this the case: elsewhere, your car has been driven there to begin with. With the petrol held in that tank alone, it's drained and flushed on the spot, and nothing more is needed.
Ignition on, or started for a second. Once primed, your system has pulled petrol out of the tank up to your filter and the lines. Drain, flush, see to the fuel filter: still normally simple.
Those few miles driven were your pump labouring on fuel diluted by petrol the whole way. Distance is only half of that; how hard it was driven counts equally. Either way this work runs to your tank, the fuel lines, the fuel filter and clean fuel through the whole system. Short trips, like the school run to the local primary school, are one thing. Any mileage on the M4, under 25 miles from Pen-y-Darren, means your engine has worked hard throughout, and a run to Newport, under 25 miles away, makes a very different task too.
Driven on until it complained — knocking, smoke, an uneven idle, a soft throttle. That's the motor telling you its fuel has stopped acting like diesel. Leave it wherever it stops: a lay-by, a quiet street, the verge on Plantation Close. The fuel drain and flush-through still go first, and they take care of it: if a vehicle is stopped early, permanent damage is very rare.
What Pen-y-Darren people get told about petrol in a diesel — and the myths in it
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing is removed by topping up — you are left with a fuller tank, still the same mix. Percentage isn't how a diesel fuel system copes with petrol, however much that advice presumes.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. At higher pressure, through smaller parts: that is how a modern diesel handles its fuel, so the lubrication counts more, not less.
One myth that catches drivers out: if it starts and drives, it must be unharmed. Diesel in a petrol motor usually means a motor that won't run: the driver stops, and so does the harm. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually does; meanwhile the pump wears. A running engine does not mean fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a distinct fault. It doesn't put back what petrol has diluted, and the petrol is still inside that tank later on.
The next start draws petrol back round your pump from the lines and the fuel filter, where some of that sits after the engine has been run. That is why draining your tank yourself does not sort it — a myth. Also, a can of petrol filled at the roadside is truly risky.
How it happens: petrol in a diesel
Nobody does it on purpose, and it's rarely carelessness. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle generally will not go into a petrol motor at all. So the error runs one way.
The moment habit stops matching the vehicle is the moment it occurs. A motor that's new to you — hired, on loan as a courtesy car, or just bought. Households running one of each, petrol and diesel. A forecourt you know, only with its pumps arranged differently. A train to catch, and a rushed fill en route to Merthyr Tydfil. A new-to-you diesel Renault Megane, its first fuelling, and a motorist accustomed to petrol: precisely when it takes place. With rain, a call coming in, or a car full of children to deal with, your hand just does what it always has.
Pen-y-Darren motorists: how to avoid petrol in a diesel next time
- Read the pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on every forecourt. The label is what matters.
- In a car you do not know, look inside the flap over your filler or at the cap before your first fill: plenty of vehicles print the fuel type there.
- One of each in the house? Label the key to your diesel — a bright fob, a sticker — since intending to remember is not enough.
- It seems daft and it works: on your first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the pump.
- Mistakes like this are easy to make while your mind is on something else, so your phone goes away.
- Some diesels come with a filler designed to reject a petrol nozzle, and devices you can add exist for motors without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop reading the petrol pump.
- Less petrol makes a weaker mix, so stop as soon as you notice — while remembering that your next step is unchanged. It's still not to fire it up.
Put petrol in a diesel in Pen-y-Darren already?
Then, there is just a short order of things. Starting it is out, and so is turning on the ignition. If you are still at the forecourt — Esso or anywhere else — ask the staff to help you push it clear of the petrol pump. What got in, roughly how much, and whether it's run: tell us those when you ring 0333 366 0103.
If it was AdBlue and not petrol, say so. That is a different issue — corrosion and deposits rather than lost lubrication — and it has its own page for Pen-y-Darren.
Why one petrol in a diesel job in Pen-y-Darren costs more than another
There is no honest single quote for this, since the four situations above are four separate tasks. The situation itself does most of the work of moving your cost. Two things follow that: the petrol that was put in as a share of what the tank takes, then the place your car is in and whether our van can reach it safely.
That is why we ask three queries before costing rather than after: what got in, how much, and if it's run. Given those answers, there is a straight figure rather than a range.
About Pen-y-Darren and where it is
Pen-y-Darren is a suburban area in Merthyr Tydfil, situated on the riverside at an elevation of 232 metres. Pen-y-Darren lies near the communities of Penyard, Incline Top, and Morgan Town, and is located approximately 19.7 miles from Newport. Pen-y-Darren has a population of around 5296 people, predominantly residing in terraced housing. Pen-y-Darren is also relatively close to major cities, with London being around 140 miles away.
Across Merthyr Tydfil and around Pen-y-Darren: fuel drain cover
Pen-y-Darren sits in the CF postcode area, and the teams that answer petrol in diesel call-outs there work the locations around it as well — Penyard, Incline Top and Morgan Town among them. A forecourt, a supermarket car park, a lay-by or your own drive are all locations our engineers drain, and the vehicle does not need to come to us.
At the pump around Pen-y-Darren, still?
Nothing beats it: that's where you are. Keep it off. Ring.