Figheldean: Petrol in a Diesel Car? How Worried to Be
Less than you probably are, if it hasn't been started. Until the ignition primes the pump, the starter turns, or your car is driven, petrol in a diesel tank simply rests there and does no harm. Which means the truthful reply to that first Figheldean query — "have I ruined it?" — normally no. Keep it like that: leave your motor off then phone Petrol in Diesel. The remainder of this page explains what petrol really does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you a second time.
Inside the engine: what petrol in a diesel really does
Diesel does two jobs on its way through a motor. It burns, and before it ignites it lubricates. Very fine tolerances are built into your injectors and the high-pressure fuel pump, and only the diesel flowing through keeps those surfaces from grinding together.
Of those two jobs, petrol handles the first poorly and the second not at all. The rattling comes from petrol being made not to ignite when compressed, which is exactly the opposite of what a diesel needs. On top of that it is runnier than diesel, it strips out the lubrication the fuel system hinges on, and any pump working on that mix is wearing itself.
Together, those make 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. The beginning of a mechanical one is a pump that has been working on that petrol — and whatever a worn pump sheds travels on with your fuel to your injectors beyond it.
Petrol in a diesel around Figheldean: how serious is it? Four cases
Filled up, and never started: no case is better. Being on a forecourt is what makes this possible: elsewhere, your car has been driven there to begin with. With that petrol held in that tank alone, it's cleared and purged on the spot, and nothing more is needed.
A moment's running, or merely your ignition on. Once primed, the fuel system has pulled petrol out of the tank up to your filter and the fuel lines. Usually little more than clearing, cleaning and seeing to the fuel filter, and so still simple.
Driven a couple of miles. Now your pump has spent these miles running on thinned fuel. How hard the vehicle was driven counts as much as how far, and the work takes in the tank, the lines, your filter and fresh fuel through the entire circuit. On the school run to Netheravon All Saints CofE Primary School, the miles is small. Any miles on the M4, under 25 miles from Figheldean, means the motor working hard throughout, and a run to Salisbury, under 15 miles away, is a very different job too.
Clattering, an uneven idle, smoke, a throttle gone soft: driven till it complained. The engine is telling you the fuel is no longer behaving like diesel. Stop wherever you are — the verge on Pollen Close, a lay-by, a side street — and leave the vehicle where it is. The fuel drain and flush still go first, and they deal with it: when a car is stopped quickly, long-term damage is very unusual.
Myths Figheldean people hear about petrol in a diesel
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. A bigger tank of the same mixture is all you get, because topping up takes out nothing. That guidance assumes a diesel fuel system handles petrol by percentage. It does not.
If anything, the reverse is true. Myth: "A newer diesel can cope with a bit of petrol." At higher pressure, through finer parts: that is how a modern diesel moves its fuel, so the lubrication matters for more, not less.
One myth that catches drivers out: if it starts and drives, it must be unharmed. The motorist of a petrol motor fed diesel usually has no choice but to stop, because it will not run, and the damage stops with them. Feed petrol to a diesel and it normally starts, ticks over and pulls away as if nothing has happened — all the while its pump wears. Running is not the same as fine.
Myth: a two-stroke additive makes it safe to drive home. It was an old fix, meant for another issue. None of what petrol weakened is put back by it — and afterwards, the tank still contains the petrol.
The next start sends petrol back round the pump from the lines and the filter, where some of that ends up after the engine has run. That is why a DIY tank drain does not leave you sorted — a myth. It is also truly risky to drain petrol into a can by the roadside.
How petrol ends up: petrol in a diesel
It is rarely carelessness, and nobody does it on purpose. The petrol nozzle is the narrower of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol car at all. The forecourt makes it easy, and the error runs one way.
Routine and your car getting out of step is how it happens. A new car, a hire car or a courtesy car. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a well-known forecourt. Rushing for a train at Grateley and filling up en route. A new-to-you diesel Renault Megane, its first fuelling, and a motorist accustomed to petrol: exactly when it takes place. Your hand does what it has always done once you add rain, a phone call or a back seat full of children.
Next time you fill up in Figheldean: preventing petrol in a diesel
- A green handle for unleaded and black for diesel is usual in the UK — yet not on each forecourt. Trust the label on the pump, not the colour.
- Inspect your filler flap. Plenty of cars state the fuel type inside the flap or on the cap. Look at it on your first fill in any vehicle you do not know.
- Good intentions count for less than a sticker or a fob in a vivid colour on the diesel's key when a house has one of each. So label it.
- 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 petrol pump. It sounds silly and it works.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck the phone away.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to reject a petrol nozzle, and add-on devices exist for motors without one. They are a safety net, not a reason to stop checking the petrol pump.
- Less petrol makes a weaker mixture, so stop the moment you realise — while remembering that the next stage is unchanged. It is still not to start the car.
Figheldean: already put petrol in a diesel?
In that case, there's just a short order of things. Do not turn the ignition on, and do not crank it. Ask the attendants to help you push it away from the pump if you're still at the forecourt, whether that's Esso or somewhere else. Then phone 0333 366 0103 and tell us what went in, roughly how much, and whether it has run.
If it was AdBlue and not petrol, say so. That's a separate issue — corrosion and deposits and not lost lubrication — and it has its own page for Figheldean.
One petrol in a diesel job in Figheldean costs more than another. Why?
The four situations above are four different jobs, so no single quote for this would be fair. Which of them you're in is chiefly what moves your cost. The proportion matters next, meaning how much of the tank is petrol, and then the position of the car and whether reaching it is safe for our van.
Ahead of any quote, not after, we ask three queries: your fuel that got in, the amount, and whether it's run. That's why. Those replies turn a range into a straight figure.
About Figheldean
Figheldean is a village in Wiltshire, situated on the banks of the River Avon at an elevation of around 87 metres. Figheldean lies near the city of Salisbury, approximately 10 miles to the northwest, and is surrounded by other small villages such as Alton and Ablington. Figheldean has a population of around 536 people, predominantly living in detached houses. Figheldean is located in the South West region of England, about 74 miles west of London.
Fuel drain cover across Wiltshire, Figheldean included
Alton, Ablington and Milston are among the spots near Figheldean that the same vans work, answering petrol in diesel jobs across Figheldean's SP postcode area. Our engineers drain where your car is — your own drive, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
In Figheldean and still at the pump?
In that case, you couldn't be in a better position. Phone, and leave it turned off.