Should You Worry? Petrol in a Diesel Car in Nuffield
Far less than you probably are, if it hasn't been started. Petrol sitting in a diesel tank does nothing to the motor until something pulls it through your fuel system — your ignition priming your pump, your starter, or the drive itself. So the honest answer to the first question anyone in Nuffield asks, "have I ruined it?", is generally no. To leave it like that, ring Petrol in Diesel and leave your motor alone. The rest 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 doesn't happen to you again.
Your engine and petrol in a diesel: what goes on
Diesel does two jobs on its way through an engine. Before it burns, it protects — and then it ignites. Very fine tolerances go into the fuel injectors and the high-pressure pump, and only the diesel running through stops those surfaces grinding together.
The second task petrol does not do at all, and the first it does badly. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump on that mixture to wear itself. It is also made to resist igniting under compression — the opposite of what a diesel needs — which is why you hear the clattering.
The shape of the issue is clear once you put those together. The damage is done by movement, not by contact. Petrol in the tank is a fuel problem. The start of a mechanical one is a pump that has been working on that petrol — and whatever a worn pump sheds moves on with the fuel to the injectors downstream.
Four scenarios our technicians see around Nuffield: how serious is petrol in a diesel?
Fuelled, and not started: no case is better. Just that tank has petrol in it, and so the job is clearing your tank and purging the fuel system where the car sits. This scenario can only really occur on a forecourt: anywhere else, your car got there by being driven.
Started for a moment, or only the ignition on. The system has been bled, so petrol has left your tank and reached the filter and the lines. Normally little more than clearing, cleaning and sorting the fuel filter, and so still easy.
Driven a couple of miles. Now your pump has spent these miles working on diluted fuel. How hard the car was driven matters as much as how far, and the work takes in your tank, the fuel lines, your filter and fresh fuel through the entire system. Short trips, such as the school run to Canford Heath Junior School, are one matter. Getting as far as Salisbury, under 25 miles away, makes a very different job — as does any distance on the M27, under 25 miles from Nuffield, with the engine running hard the whole time.
Driven until it complained. Rattling, an uneven idle, smoke, a throttle that has gone soft. What you are hearing is your engine signalling fuel that no longer runs like diesel. Pull up where you are — on the verge on Hatch Pond Road, at the kerb, down a side road — and don't move it. The drain and flush still go first, and they sort it out: if a vehicle is stopped soon, permanent damage is very uncommon.
Nuffield motorists and the petrol in a diesel myths they hear
False: topping up to full with diesel makes it fine. It doesn't. A bigger tank of the same mix is all it gives, since topping up takes out nothing. The assumption behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
"Newer diesels can handle a little petrol" — a myth, and nearer the opposite. A modern diesel runs its fuel through more precise components at higher pressure, which makes the lubrication matter more, not less.
This is the one that catches motorists. Myth: "If it starts and drives, there's no damage done." Feed diesel to a petrol motor and it normally won't run, and so the motorist stops — and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually does; meanwhile your pump wears. Running does not mean fine.
Myth: "Add some two-stroke oil and drive it home." It's an old fix for a separate issue. It does not put back what petrol has thinned, and the petrol is still in that tank later on.
Myth: "Drain your tank yourself and you're sorted." After the motor has run, some of the petrol is no longer inside that tank: it's in your filter and your lines, and it goes straight back through your pump on your next start. Emptying petrol into a can at the roadside is also genuinely dangerous.
How does petrol in a diesel take place?
A careless moment is seldom the cause, and no one means to do it. The forecourt makes it simple: the petrol nozzle is the slimmer of the two, and it slides into a diesel filler with almost no resistance, while a diesel nozzle mostly won't go into a petrol car at all. So the error runs one way.
It occurs when routine and your car stop matching. Hire cars, courtesy cars, and cars that are new to you. A household with one petrol and one diesel on the drive. Your ordinary forecourt, its pumps suddenly in a different order. Racing for a train outside Poole and fuelling up en route. A new-to-you diesel Volkswagen Golf, its first fuelling, and a driver used to petrol: exactly when it happens. With rain, a call arriving, or a car full of children to deal with, the hand simply does what it has always done.
Next time you fill up around Nuffield: avoiding petrol in a diesel
- The label is what matters, so check the pump rather than the colour: in the UK unleaded handles are normally green and diesel black, but not on every forecourt.
- Inspect the filler flap. Many vehicles state the fuel inside the flap or on the cap. Look at it on the first fill in a car you don't know.
- Mark the key. In a household with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of intending to remember.
- Before the nozzle comes off the pump the first time you fill a hired or new motor, say "diesel" out loud. Daft, perhaps, but it does the trick.
- While you're thinking about something else, this is an easy mistake to make — so tuck the phone away.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler designed to block a petrol nozzle, and add-on devices are available for the rest. Count it as a backstop, then keep checking the pump.
- The moment you notice, stop: less petrol in the tank makes a thinner blend. What to do next does not change, though — still do not start it.
Petrol already in a diesel in Nuffield? Begin here
Then the order of things is brief. Don't turn the ignition on, and don't start it. Ask the staff to help you roll it away from the petrol pump if you are still on the forecourt, whether that is Shell or somewhere else. Next, 0333 366 0103. We will ask what got in, about how much, and if it has been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a separate problem — Nuffield has a page all for it.
One petrol in a diesel task around Nuffield costs more than another. Why?
The four situations above are four different tasks, so no single price for this would be honest. Which of them you're in is chiefly what moves the cost. The proportion counts next, meaning how much of that tank is petrol, followed by the location of the vehicle and whether getting to it is safe for a technician.
Ahead of any quote, not after, we ask three queries: the fuel that got in, its amount, and whether it's run. That's why. With those answers, you get a straight figure instead of a range.
About Nuffield
Nuffield is a small suburban area located on the coast of Dorset, with an elevation of approximately 6 metres above sea level. Nuffield sits near the towns of Waterloo and Stanley Green, and is part of the larger area surrounding Poole. Nuffield is characterized by its predominantly detached housing stock, reflecting the area's residential nature.
Fuel drain cover across Dorset, Nuffield included
Petrol in diesel calls in Nuffield — part of the BH postcode area — go to vans that also cover the spots around it, Waterloo, Stanley Green and Canford Heath included. The vehicle does not need to come to us: our technicians drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Nuffield: still at the petrol pump?
Then you're in the best place there is. Keep it off. Phone.