Trehafren: Petrol in a Diesel Car? How Worried to Be
If it hasn't been started, you can worry less than you likely are. Petrol sitting in a diesel tank does nothing to your engine till something pulls it through the fuel system — your ignition priming your pump, the starter, or driving itself. So the fair answer to the first question anyone in Trehafren asks, "have I wrecked it?", is normally no. Petrol in Diesel is who to phone, with your motor left off, so it remains that way. The remainder of this page sets out what petrol really does to a diesel, how to tell how far it has got, and how to make sure it does not happen to you again.
What petrol in a diesel does to the engine
On its way through an engine, diesel does two tasks. Before it combusts, it lubricates — then it ignites. Very fine clearances go into the injectors and the high-pressure fuel pump, and only your diesel running through keeps those surfaces from grinding together.
The second task petrol does not do at all, and the first it does badly. The clattering comes from petrol being made not to ignite when compressed, which is exactly the reverse of what a diesel needs. On top of that it is thinner than diesel, it strips away the protection the fuel system rests on, and any pump working on that blend is wearing itself.
Taken together, they show what shape the trouble has. The harm is done by circulation, not by contact. A tank with petrol in it is a fuel issue. After the pump has been working on that petrol, a mechanical fault has started: whatever is shed by a pump that's wearing down travels onward to the fuel injectors with your fuel.
Trehafren, petrol in a diesel: four cases, from mild to serious
Fuelled, and not started: nothing beats it. On a forecourt, and truly only there, the petrol is still confined to that tank — because everywhere else the vehicle was driven to get to it. The job is emptying and purging on the spot.
A brief spell of running, or just the ignition on. Once primed, the system has drawn petrol out of your tank as far as the fuel filter and the lines. Usually nothing more than emptying, cleaning and seeing to the fuel filter, so still easy.
Your pump now spent a couple of miles on diluted fuel — that is what driving the car does. How hard the vehicle was driven matters as much as how far, and the work covers the tank, the fuel lines, the filter and fresh fuel through the whole system. Driving the children to the local primary school is one sort of trip. A run as far as Wrexham, under 50 miles away, is a very different job. So is any mileage on the M54, under 50 miles from Trehafren, where your engine has been working hard the whole time.
It protested, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone lumpy. That's your engine telling you its fuel has stopped acting like diesel. Leave it where it stops: a lay-by, a quiet street, the verge on Lon Cerddyn. A vehicle stopped soon very rarely has permanent damage, as the fuel drain and the flush, which still go first, deal with it.
Myths Trehafren people hear about petrol in a diesel
Myth: topping up to full with diesel makes it fine. It doesn't. Nothing comes out when you top up — that tank just holds more of the same mixture. That guidance supposes a diesel fuel system tolerates petrol by percentage. It doesn't.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. A newer diesel sends its fuel through finer parts at higher pressure, which makes the protection count more, not less.
"It starts, it drives, and so no harm done" — the myth that trips up most drivers than any other. Feed diesel to a petrol engine and it generally won't run, and so the driver stops — and the harm stops with them. Whilst the pump wears, a diesel fed petrol normally starts, idles and drives away as if nothing has happened. Running is not the same as fine.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an old workaround for a different issue. None of what petrol thinned gets put back by it — and later, the tank still contains the petrol.
The next start sends petrol back round the pump out of your lines and your filter, where some of it sits after the engine has been run. That is why draining your tank yourself doesn't sort it — a myth. It is also genuinely risky to drain petrol into a can by the roadside.
How does petrol in a diesel take place?
Carelessness is seldom the cause, and no one means to do it. One way only, since of the nozzles: the narrower petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one mostly will not fit a petrol vehicle. That is how the forecourt makes it simple.
It happens when habit and the car stop matching. A vehicle that is new to you — hired, on loan as a courtesy car, or brand new. Households running one of each, petrol and diesel. The pumps in a different order on a familiar forecourt. A hurried fill on the way to Newtown (Powys) with a train to catch. Years of petrol vehicles behind you, a diesel Volkswagen Tiguan in front of you at the forecourt for its first tank — that's when. With rain, a call coming in, or children to deal with, your hand just does what it has always done.
Next time you fill up in Trehafren: preventing petrol in a diesel
- Read the petrol pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on every forecourt. The label is what counts.
- In a vehicle you don't know, look inside the flap over the filler or at the cap before your first fill: plenty of vehicles state the fuel there.
- A coloured fob or a sticker on your diesel's key does more than any amount of intending to remember, in a house with one of each.
- It sounds silly and it does the trick: on your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump.
- Thinking about something else is when this becomes an easy mistake to make, so put the phone away then keep your mind on the petrol pump.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler built to refuse a petrol nozzle, and add-on devices are available for the remainder. Treat it as a backstop, then keep reading the pump.
- Less petrol means a thinner mix, and so stop the moment you notice — though remembering that your next step is unchanged. It's still not to fire it up.
Put petrol in a diesel around Trehafren already?
In that case, there's just a short order of things. Don't switch your ignition on, and don't crank it. If you are still at the forecourt — BP or anywhere else — ask the staff to help you push the car away from the petrol pump. What went in, about how much, and whether it has run: tell us those when you ring 0333 366 0103.
Say so if it was AdBlue rather than petrol: it is a separate issue, with its own page for Trehafren, since AdBlue brings corrosion and deposits instead of lost lubrication.
What makes one Trehafren petrol in a diesel task cost more than the next
There is no fair single price for this, since the four scenarios above are four separate tasks. Which of them you are in is chiefly what shifts your cost. Beyond that it's the ratio — how much petrol got in against how much your tank holds — and after that where the vehicle is and whether a van can reach it safely.
That is why our engineers ask three queries before quoting rather than after: what went in, how much, and if it has run. With those answers, there is a straight figure rather than a range.
About Trehafren, for a moment
Trehafren is a suburban area situated on the riverside in Powys, Wales, with an elevation of 138 metres. Trehafren has a mix of housing types, but is predominantly characterised by terraced homes. Trehafren is located near several smaller communities, including Milford, Garth Owen, and Maesyrhandir, and is within commuting distance of Wrexham. Trehafren is a relatively small but established community, with a population of around 3601 residents.
Across Powys and around Trehafren: fuel drain cover
Milford, Garth Owen and Maesyrhandir are among the places near Trehafren that the same teams work, answering petrol in diesel call-outs across Trehafren's SY postcode area. The vehicle doesn't need to move to us: our engineers drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
In Trehafren and still at the petrol pump?
No position is better: that is where you are. Phone, and keep it switched off.