Hunston: Petrol in a Diesel Car? How Worried to Be
Not started? Then less worried than you likely feel. Until the ignition primes the pump, your starter cranks, or the car is driven, petrol in a diesel tank simply sits there and does no harm. Which makes the honest reply to that first Hunston question — "have I wrecked it?" — usually no. To leave the vehicle like that, call Petrol in Diesel then leave your motor alone. The rest of this page covers 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.
Petrol in a diesel: what does it do to your engine?
Two jobs fall to diesel on its journey through a motor. It ignites, and before it combusts it protects. What stops the surfaces inside your high-pressure pump and your injectors from wearing down against one another is your diesel passing through them — they're made to very fine clearances.
Petrol does the first task poorly and the second not at all. It is thinner than diesel and removes the protection the system depends on, and so a pump running on a petrol mixture 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 rattling comes from.
Taken together, they show the shape the trouble has. Not contact but circulation is what causes the harm. Petrol in the tank is a fuel issue. After your pump has been running on that petrol, a mechanical problem has begun: whatever is shed by a pump that is grinding is carried onward to your injectors with the fuel.
Hunston, petrol in a diesel: four situations, from mild to significant
Fuelled but not once started — the best it gets. Being on a forecourt is what makes this possible: elsewhere, the car has been driven there to begin with. With the petrol kept in that tank alone, it is drained and purged right where it stands, and nothing more is needed.
Started for a moment, or only the ignition on. The fuel system has been bled, so petrol has left your tank and got to the filter and the fuel lines. Drain, flush, deal with the filter: still usually easy.
Those few miles on the road meant the pump working on fuel weakened by petrol the whole way. How hard your car was driven counts as much as how far, and this work takes in your tank, the fuel lines, the filter and fresh fuel through the whole circuit. On the school run to North Mundham Primary School, the distance is short. Very different a second time: a trip to Chichester, under 3 miles away, or any mileage on the Waterlooville Bypass, under 15 miles from Hunston, where your engine kept running hard.
Knocking, a ragged idle, smoke, a throttle gone soft: driven till it complained. The engine is telling you the fuel is no longer acting like diesel. Whether it's the verge on Jestico's Close, a lay-by or a side road, stop where you are then leave it. A car stopped quickly very seldom has permanent damage, because the fuel drain and the flush, which still come first, sort it out.
What Hunston motorists get told about petrol in a diesel — and the stories in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." Topping up removes nothing; it gives you a fuller tank of the same mix. The assumption behind that guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: a modern diesel copes with a bit of petrol. If anything, the reverse. Finer parts and higher pressure are the way a current diesel runs its fuel, and that makes the lubrication matter more, not less.
The myth that catches drivers off guard: if it starts and drives, it must be unharmed. The motorist of a petrol engine fed diesel usually has no choice but to stop, since it will not run, and the harm stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually will; meanwhile the pump grinds. A running engine does not mean fine.
Myth: "Add some two-stroke oil and drive the car home." It is an outdated fix for a separate problem. It doesn't put back what petrol has diluted, and the petrol is still inside the tank after that.
The next start draws petrol back round your pump from the fuel lines and the filter, where some of that sits after your engine has run. That's why a DIY tank drain doesn't leave you sorted — a myth. Clearing petrol into a can by the kerbside is also truly hazardous.
Petrol in a diesel: how does it occur?
On purpose? Never. Through carelessness? Seldom, if ever. One way only, since of the nozzles: the slimmer petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one mostly won't fit a petrol vehicle. That is how the forecourt makes it easy.
When habit and the car stop matching, it takes place. Courtesy car, hire car, or a vehicle that is new. Two cars on one driveway, one petrol, one diesel. The pumps in a different order on a familiar forecourt. Racing for a train outside Chichester and fuelling up en route. Exactly the moment it occurs: after years of driving petrol, a driver fills a diesel Volkswagen Tiguan for the first time. Throw in a back seat full of children, a phone call or rain, and habit takes over.
Preventing petrol in a diesel next time you fill up around Hunston
- 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.
- Plenty of motors state the fuel type inside your filler flap or on the cap, and so check there on the first fill in any car you do not know.
- Good intentions do less than a sticker or a fob in a vivid colour on your diesel's key if a house has one of each. So mark it.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the petrol pump. It sounds daft and it does the trick.
- Mistakes like this are simple to make while your mind is on something else, so your phone goes away.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to block a petrol nozzle, and aftermarket devices exist for the rest. Count it as a backstop, then keep reading the pump.
- Stop the moment you notice. Less petrol in the tank makes a thinner mixture. It doesn't change what to do next, which is still not to crank it.
Petrol already in a diesel in Hunston? Begin here
Short and simple, then, is the order of things. Don't switch your ignition on, and do not crank it. Ask the attendants to help you push it clear of the petrol pump if you are still on the forecourt, whether that is Esso or somewhere else. Next, 0333 366 0103. We'll ask what was put in, about how much, and if it's been run.
If it was AdBlue rather than petrol, say so. That's a separate problem — corrosion and deposits rather than lost protection — and it has its own page for Hunston.
One petrol in a diesel task around Hunston costs more than another. Why?
There is no honest single quote for this, since the four scenarios above are four different tasks. Chiefly, your cost shifts with which one you're in. Where the vehicle is matters too, and whether our van can safely reach it, after the share of petrol to what your tank holds.
Before any quote, not after, come three queries: your fuel that was put in, the amount, and if it's run. That is why. Their replies are what turn a range into one firm number.
About Hunston
Hunston is a small village in West Sussex, situated near the coast and close to the city of Chichester. Hunston has a low elevation of around 4 metres, and its location near the sea has influenced its development. Hunston is characterized by its terraced housing and is part of a network of nearby villages, including Donnington and North Mundham. Hunston is also within commuting distance of London, being approximately 55.7 miles away.
Across West Sussex and in Hunston: fuel drain cover
Hunston sits in the PO postcode area, and our vans that answer petrol in diesel jobs there work the places near it as well — Donnington, North Mundham and Stockbridge among them. Our technicians 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.
In Hunston and still at the petrol pump?
The best position there is, then — that's where you are. Leave the car switched off, then ring.