Fintona: Petrol in a Diesel Car? How Worried to Be
Not started? Then less anxious than you likely feel. Until the ignition primes the pump, the starter cranks, or your vehicle is driven, petrol in a diesel tank simply rests there and does no harm. Which makes the truthful reply to the first Fintona query — "have I wrecked it?" — usually no. To leave the car that way, call Petrol in Diesel and leave the motor alone. What petrol really does to a diesel, how to judge how far it's gone, and how to stop it from happening a second time: that is the remainder of this page.
Petrol in a diesel: what does it do to your engine?
On its way through a motor, diesel does two jobs. Oiling comes before burning; it does both. The high-pressure fuel pump and the fuel injectors are designed to very fine clearances, and your diesel passing through them is what stops those surfaces from grinding against one another.
Poorly at the first, not at all at the second: that's petrol. It is thinner than diesel and takes away the lubrication your fuel system rests on, and so a pump running on a petrol mix is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That is where the knocking comes from.
Put these together and the shape of the problem is clear. Not contact but circulation is what does the harm. Petrol in a tank is a fuel problem. The start of a mechanical problem is a pump that has been working on that petrol — and whatever a worn pump sheds travels on with the fuel to the injectors downstream.
Four scenarios we see around Fintona: how bad is petrol in a diesel?
The best case there is: filled up, not once started. Just your tank has petrol in it, and so the task is clearing the tank and rinsing your system where your car sits. This scenario can only really occur at a forecourt: anywhere else, the car got there by being driven.
A moment's running, or merely the ignition on. The system has been primed, and so petrol has left the tank and reached the fuel filter and your lines. Still generally straightforward: drain, flush, and the fuel filter sorted.
Those few miles on the road meant your pump labouring on fuel thinned by petrol the whole way. Distance is only half of it; how hard it was driven matters just as much. Either way the work runs to that tank, your lines, the filter and fresh fuel through the whole system. Driving the children to the local primary school is one sort of trip. Any miles on the M77, over 50 miles from Fintona, means the motor working hard throughout, and a run to Armagh, under 50 miles away, is a very different job as well.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone lumpy. The engine is telling you your fuel is no longer behaving like diesel. Whether it's the verge on Wallace Cottages, a lay-by or a side road, stop where you are and leave it. The drain and flush still come first, and they deal with it: if a car is stopped quickly, lasting damage is very uncommon.
Fintona people and that petrol in a diesel stories they hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. A bigger tank of the same mixture is all you get, because topping up removes nothing. The assumption behind that advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
Not so: a current diesel copes with a bit of petrol. Rather, the reverse. A modern diesel runs its fuel through smaller parts at higher pressure, which makes the protection count more, not less.
This is the one that fools motorists. Myth: "If it starts and drives, there's no harm done." Diesel in a petrol motor normally means a motor that will not run: the driver stops, and so does the damage. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually will; meanwhile your pump wears. A running engine does not mean fine.
Not so: a two-stroke additive makes it safe to drive home. It is an old workaround, supposed for another issue. It doesn't put back what petrol has weakened, and that petrol is still in your tank afterwards.
The next start draws petrol back round your pump out of the fuel lines and the filter, where some of it sits after the motor has been run. That's why draining your tank yourself does not sort it — a myth. It's also genuinely dangerous to drain petrol into a can by the roadside.
How petrol ends up: petrol in a diesel
It is seldom carelessness, and no one does it on purpose. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slips into a diesel filler with almost no resistance, whilst a diesel nozzle generally will not go into a petrol car at all. So the error runs one way.
When routine and your car stop matching, it occurs. Any vehicle that is new to you — hired, on loan as a courtesy car, or just bought. A household with one petrol and one diesel on the driveway. Your usual forecourt, its pumps now in a different order. Filling up in a hurry on the way to the nearest station, with a train to catch. Years of petrol cars behind you, a diesel Renault Clio in front of you at the forecourt for its first tank — that is when. Throw in rain, a phone call or a back seat full of kids, and the hand does what it has always done.
Next time you fill up around Fintona: preventing petrol in a diesel
- 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.
- In a motor you do not know, look inside the flap over your filler or at the cap before the first fill: plenty of motors state the fuel there.
- Good intentions do less than a sticker or a fob in a vivid colour on the diesel's key when a household has one of each. So label it.
- "Diesel", out loud, before you pick up the nozzle — every time a new or hired car gets its first tank. It sounds silly. It works.
- Thinking about something else is when this becomes an easy mistake to make, and so tuck the phone away and keep your mind on the petrol pump.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler designed to refuse a petrol nozzle, and aftermarket devices are available for the rest. Count it as a backstop, and keep reading the petrol pump.
- Stop as soon as you realise. Less petrol in that tank makes a thinner mix. It does not change what to do next, which is still not to fire it up.
Already put petrol in a diesel around Fintona?
Short and simple, then, is the order of things. Don't switch your ignition on, and don't fire it up. If you are still at the forecourt — the nearest petrol station or anywhere else — ask the staff to help you roll the car away from the petrol pump. Next, 0333 366 0103. We will ask what got in, about how much, and if it has been run.
If it was AdBlue instead of petrol, say so. That is a different fault — corrosion and deposits rather than lost lubrication — and it has its own page for Fintona.
Why one petrol in a diesel job in Fintona costs more than another
Four separate tasks sit behind the four situations above — which is why there is no fair single quote. Which of them you're in is chiefly what shifts your cost. Where the vehicle is counts too, and whether a van can safely reach it, after the proportion of petrol to what that tank holds.
What went in, how much, and if it has run — three questions our engineers ask before costing, not after, for exactly that reason. Their answers are what turn a range into one firm number.
About Fintona, for a moment
Fintona is a small locality in County Tyrone, situated inland at an elevation of 109 metres, approximately 28.5 miles from Armagh. Fintona is characterised by its terraced housing and is located near other small settlements such as Seskinore, Eskra, and Gortaclare. Fintona has a population of around 1217 people and is a considerable distance from London, at 363.1 miles away.
Fuel drain cover around Fintona and across County Tyrone
Fintona sits in the BT postcode area, and the vans that answer petrol in diesel call-outs there work the locations around it as well — Seskinore, Eskra and Gortaclare among them. Our engineers drain wherever your car is — your own drive, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
Still at the pump in Fintona?
Nothing beats it: that is where you now are. Keep it off. Call.