Should You Worry? Petrol in a Diesel Car in Aberystwyth
Likely less than you already are — provided nobody has started it. Till the ignition primes the pump, your starter turns, or your car is driven, petrol in a diesel tank simply rests there and does nothing. Which means the truthful reply to that first Aberystwyth question — "have I ruined it?" — normally no. To leave the car like that, ring Petrol in Diesel then leave the engine switched off. Further down, this page sets out what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to the engine?
On its way through a motor, diesel has two tasks. It lubricates to begin with, and only then does it burn. What keeps the surfaces inside the high-pressure fuel pump and the fuel injectors from grinding against one another is the diesel flowing through them — they're designed to extremely fine tolerances.
Of these two tasks, petrol handles the first badly and the second not at all. It is thinner than diesel and removes the protection your fuel system depends on, so a pump running on a petrol mixture is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That's where the knocking comes from.
Together, those leave the shape of the issue plain. The harm is done by circulation, not by contact. All a tank with petrol in it amounts to is a fuel issue. Whatever a worn pump sheds travels on, carried by your fuel, into your injectors further along, which is why a pump that has been working on the petrol is where a mechanical problem starts.
Four situations our engineers see in Aberystwyth: how bad is petrol in a diesel?
The best case there can be: filled up, never started. Just your tank has petrol in it, so the task is clearing the tank and flushing the system where the car stands. This situation can only truly take place on a forecourt: anywhere else, the car got there by being driven.
Started for a second, or just the ignition on. Petrol has come out of the tank and got to your filter and your lines, since the fuel system has been bled. Drain, flush, deal with your filter: still usually easy.
A few miles driven, and your pump has spent each of them labouring on diluted fuel. The work is the tank, the lines, the filter and clean fuel through the whole circuit, and how hard your car was driven matters as much as how far. On the school run to the local primary school, the mileage is small. A run as far as Swansea, over 50 miles away, is a very different task. So is any miles on the M4, under 50 miles from Aberystwyth, where the motor has been working hard throughout.
Driven on till it protested — rattling, smoke, a ragged idle, a dead throttle. That's your engine telling you its fuel no longer is behaving like diesel. Leave it where it stops: a lay-by, a quiet street, the verge on Great Darkgate Street. The fuel drain and flush-through still go first, and they sort it out: if a car is pulled over soon, long-term damage is very rare.
What Aberystwyth people 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." Topping up removes nothing; it gives you a bigger tank of the same mix. The assumption behind that guidance — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: a newer diesel copes with a bit of petrol. Rather, the reverse. Protection matters more on modern diesels, not less, since their fuel runs through finer parts at higher pressure.
Myth: "If it starts and drives, there is no damage done." This is the one that catches drivers. The driver of a petrol motor fed diesel usually has no choice but to stop, because it will not run, and the harm stops there. Feed petrol to a diesel and it usually fires up, idles and pulls away like nothing happened — all while its pump is wearing. Fine and running aren't the same thing.
An old workaround for a separate issue lies behind this one. Myth: "Add some two-stroke oil and drive it home." It does not put back what petrol has weakened, and that petrol is still inside your tank later.
The next start draws petrol back round your pump out of the lines and the filter, where some of that sits after your engine has been run. That is why a DIY tank drain doesn't sort it — a myth. Draining petrol into a can at the roadside is also really hazardous.
How it happens: petrol in a diesel
Carelessness is rarely the cause, and nobody means to do it. A diesel nozzle mostly won't fit a petrol vehicle, but the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake simple, and just in that direction.
When routine and the vehicle stop matching, it takes place. Hire cars, courtesy cars, and cars that are new to you. A household with one petrol and one diesel on the drive. The pumps in a different order on a well-known forecourt. Racing for a train outside the nearest station and fuelling up en route. A new-to-you diesel Renault Megane, its first fuelling, and a motorist used to petrol: precisely when it occurs. With rain, a call arriving, or children to deal with, the hand simply does what it has always done.
Aberystwyth motorists: how to prevent petrol in a diesel next time
- A green handle for unleaded and black for diesel is usual in the UK — but not on every forecourt. Trust the label on the pump, not the colour.
- Many motors state the fuel inside your filler flap or on the cap, so check there on the first fill in a car you do not know.
- One of each in the household? Label the key to the diesel — a coloured fob, a sticker — since intending to remember isn't enough.
- "Diesel", out loud, before you pick up the nozzle — every time a new or hired car needs its first tank. It seems silly. It does the trick.
- Thinking about something else is when this becomes an easy mistake to make, so tuck the phone away and keep your mind on the pump.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler built to refuse a petrol nozzle, and aftermarket devices are available for the rest. Treat it as a safety net, and keep checking the petrol pump.
- The moment you realise, stop: less petrol in the tank means a thinner mix. What to do next doesn't change, though — still do not crank it.
Petrol already in a diesel in Aberystwyth? Begin here
The order of things is short, then. Leave it unstarted, with the ignition switched off as well. Ask the staff to help you roll it clear of the petrol pump if you are still at the forecourt, whether that is Texaco or somewhere else. Ring 0333 366 0103 next, with three answers — your fuel, the approximate amount, and whether it's run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a different fault — Aberystwyth has a page all for it.
What makes one Aberystwyth petrol in a diesel job cost more than the next
A fair single quote doesn't exist here: four situations, four separate tasks. What shifts the cost is mostly which of them you are in. Two things come after that: the petrol that went in as a share of what the tank takes, then the spot the car is in and whether a van can get to it safely.
What was put in, how much, and if it's run — three questions our technicians ask before costing, not after, for exactly that reason. Those answers change a range into a straight figure.
About Aberystwyth
Aberystwyth is a significant coastal town in Wales, situated in the county of Ceredigion. It is notable for being home to a major university and boasts a seaside location. The town is also the largest settlement in its county, with nearby Aberaeron also holding administrative importance. Aberystwyth's blend of education and coastal charm makes it a unique place.
Across Ceredigion and in Aberystwyth: fuel drain cover
Our vans answering petrol in diesel calls in Aberystwyth, in the SY postcode area, equally work the locations around it, Buarth Mawr, Trefechan and Penglais included. A forecourt, a supermarket car park, a lay-by or your own drive are all places our engineers drain, and the vehicle doesn't need to come to us.
In Aberystwyth and still at the pump?
Then, you couldn't be in a better place. Leave it turned off, and ring.