Tumble: Petrol in a Diesel Car? How Worried to Be
Probably less than you already are — as long as no one has started it. Till the ignition primes your pump, your starter turns, or the car is driven, petrol in a diesel tank just sits there and does nothing. Which makes the truthful reply to the first Tumble question — "have I wrecked it?" — normally no. Petrol in Diesel is who to phone, with the motor left off, so it stays that way. Further down, you will find what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you again.
The engine and petrol in a diesel: what happens
On its way through an engine, diesel does two tasks. It lubricates first, and only then does it burn. What stops the surfaces inside the high-pressure pump and the fuel injectors from wearing down against each other is the diesel flowing through them — they're designed to extremely fine tolerances.
The second job petrol doesn't do at all, and the first it does poorly. Being less viscous than diesel, petrol strips away the protection a fuel system needs, leaving a pump running on that 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 knocking.
Combined, those leave the shape of the trouble plain. The damage is done by movement, not by contact. Where that petrol is only inside the tank, it is an issue of fuel, nothing more. Whatever a worn pump sheds goes on, borne by the fuel, into the fuel injectors further along, which is why a pump that has been working on that petrol is where a mechanical fault begins.
Tumble, petrol in a diesel: four situations, from mild to major
The best case there is: filled up, not once started. Being at a forecourt is what makes this possible: elsewhere, the car has been driven there to begin with. With the petrol held in your tank alone, it is drained and rinsed on the spot, and nothing more is needed.
Ignition on, or started for a moment. With the system primed, the fuel lines and filter already contain petrol that came from that tank. Drain, flush, see to your filter: still usually straightforward.
Those few miles on the road were the pump labouring on fuel thinned by petrol throughout. The work is the tank, the lines, the filter and clean fuel through the whole circuit, and how hard your car was driven counts as much as how far. Driving the kids to the local primary school is one sort of trip. Any mileage on the M4, under 5 miles from Tumble, means the motor working hard throughout, and a run to Swansea, under 15 miles away, is a very different job too.
Driven until it complained. Knocking, an uneven idle, smoke, a throttle that has gone soft. That's your motor telling you its fuel no longer is behaving like diesel. Whether it is the verge on Heol-y-Neuadd, a lay-by or a side road, stop there and leave it. Long-term damage is very uncommon when a car is stopped soon, and the drain and flush that still come first deal with it.
Tumble drivers and the petrol in a diesel myths they hear
False: topping up to full with diesel makes it fine. It does not. Topping up removes nothing; it gives you a bigger tank of the same mixture. The idea behind the guidance — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. A current diesel runs its fuel through more precise 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 catches people. The motorist of a petrol engine fed diesel normally stops, since it will not run, 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.
Not so: a two-stroke additive makes it safe to drive home. It is an old fix, meant for another fault. None of what petrol weakened gets put back by it — and afterwards, that tank still holds the petrol.
"Drain it yourself and you are sorted" — a myth, since after it has been running some petrol lies in the fuel filter and lines, waiting to go right back through your pump on your next start. Besides, petrol emptied into a can by the road is genuinely risky.
Petrol in a diesel: how does it happen?
A careless moment is seldom the cause, and nobody means to do it. One way only, because of the nozzles: the smaller petrol one slips inside a diesel filler with almost no resistance, whereas the diesel one generally won't fit a petrol motor. That is how the forecourt makes it simple.
Habit and your car getting out of step is when it occurs. Courtesy car, hire car, or a motor that's new. One petrol and one diesel on the driveway of the same household. Your usual forecourt, its pumps suddenly in a different order. A rushed fill on the way to Pantyffynnon with a train to catch. The first fill-up in a diesel Renault Clio after years of driving petrol is exactly the moment it occurs. Throw in rain, a phone call or a back seat full of children, and your hand does what it has always done.
Tumble drivers: how to prevent petrol in a diesel next time
- Green for unleaded and black for diesel is usual in the UK — but not on each forecourt. Go by the label on the pump, not the colour.
- Many motors state the fuel type inside the filler flap or on the cap, and so check it on your first fill in any vehicle you don't know.
- One of each in the household? Mark the key to the diesel — a coloured fob, a sticker — since meaning to remember is not enough.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the pump. It seems daft and it works.
- Thinking about something else is when this becomes an easy mistake to make, so tuck the phone away and keep your mind on the petrol pump.
- Add-on devices exist for motors without one, and some diesels come with a filler that will not accept a petrol nozzle. Helpful — but a safety net only, never a reason to stop checking the label.
- The moment you notice, stop: less petrol inside the tank means a thinner blend. What to do next doesn't change, though — still don't crank it.
Tumble: already put petrol in a diesel?
In that case, there's just a short order of things. Don't fire it up, and don't switch the ignition on. The staff on the forecourt — whether at Independent itself or wherever you filled up — will usually help roll it clear of the pump if you ask. Ring 0333 366 0103 next, with three facts — your fuel, the rough volume, and if it has run.
Corrosion and deposits are the issue with AdBlue, where petrol means lost protection. So if it was AdBlue, say so — and see its own Tumble page.
Tumble petrol in a diesel tasks: why one costs more than another
An honest single price does not exist here: four scenarios, four separate jobs. What moves the cost is chiefly which of them you're in. Where your car is matters too, and whether our van can safely get to it, after the proportion of petrol to what the tank takes.
That is why our technicians ask three questions before quoting instead of after: what got in, how much, and whether it has run. Those answers change a range into a straight figure.
About Tumble itself
Tumble is a small village in Carmarthenshire, situated on the banks of a river at an elevation of 149 metres. Tumble has a mix of housing types, but semi-detached homes are predominant, and it is located near other small communities such as Cwm-mawr and Drefach. Tumble is close to the city of Swansea, which is approximately 13.8 miles away, and it has a population of around 812 residents. Tumble is part of a wider rural area in south-west Wales, with easy access to the region's countryside and coastline.
Tumble and Carmarthenshire: where our fuel drain cover runs
Cwm-mawr, Drefach and Cwm-y-glo are among the spots near Tumble that the same teams work, answering petrol in diesel jobs across Tumble's SA postcode area. No need to bring the car to us. Forecourts, supermarket car parks, lay-bys and your own drive are all places where we work.
At the pump around Tumble, right now?
In that case, you could not be in a better place. Leave the vehicle switched off, then ring.