Caldecott: Petrol in a Diesel Car? How Worried to Be
Not started? Then less anxious than you likely are. Petrol sitting in a diesel tank does nothing to the engine till something draws it through your fuel system — your ignition priming your pump, the starter, or the drive on its own. So the honest answer to the first question everyone in Caldecott asks, "have I wrecked it?", is normally no. Leave the engine off and call Petrol in Diesel — that keeps it that way. Keep reading for three things: the effect petrol has inside a diesel engine, the clues of how far it has got, and ways to make sure you don't do it again.
Inside the engine: what petrol in a diesel really does
Diesel does two tasks on its way through an engine. It combusts, and before it burns it lubricates. Designed to very fine tolerances, the fuel injectors and the pump rely on your diesel flowing through them to stop their surfaces wearing against one another.
Petrol does the first job badly and the second not at all. It's runnier than diesel and takes away the lubrication the system rests on, so a pump running on a petrol blend 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's where the clattering comes from.
The shape of the trouble is plain once you put those together. It's circulation that does the harm, not contact. Where the petrol is only inside that tank, it's a problem of fuel, nothing more. Whatever a worn pump sheds goes on, borne by your fuel, into the injectors further along, which is why a pump that has been working on that petrol is where a mechanical issue begins.
Caldecott, petrol in a diesel: four situations, from mild to significant
The best case there can be: filled up, never started. Just that tank has petrol in it, and so the job is draining your tank and purging the fuel system where the vehicle sits. This situation can only truly occur at a forecourt: anywhere else, the vehicle got there by being driven.
A moment's running, or just your ignition on. Petrol has come out of your tank and reached the fuel filter and your lines, since the fuel system has been primed. Usually little more than draining, flushing and sorting the fuel filter, and so still simple.
Your pump has worked a few miles on thinned fuel — that is what driving the vehicle does. Tank, lines, filter, then fresh fuel run through the entire system: that is this work, and the way your car was driven matters as much as the distance. Driving the children to Caldecott Primary School is one sort of trip. Very different again: a run to Oxford, under 10 miles away, or some distance on the Wheatley Spur, under 10 miles from Caldecott, where your engine never stopped running hard.
Knocking, an uneven idle, smoke, a throttle gone soft: driven until it complained. The engine is telling you the fuel is no longer behaving like diesel. Leave it wherever it stops: a lay-by, a side street, the verge on Hermitage Road. Lasting damage is very unusual if a vehicle is pulled over early, and the drain and flush that still go first deal with it.
Myths Caldecott drivers hear about petrol in a diesel
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Nothing is removed by topping up — you're left with a bigger tank, still the same mixture. A diesel fuel system does not tolerate petrol by percentage in the way that advice supposes.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. Finer components and higher pressure are how a modern diesel runs its fuel, and that makes the lubrication matter more, not less.
"It starts, it drives, and so there is no harm" — the myth that catches more drivers than any other. The motorist of a petrol engine fed diesel usually has no choice but to stop, because it will not run, and the harm stops there. A diesel fed petrol usually starts, idles and drives away as if nothing has happened, whilst the pump grinds. Running does not mean fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a separate issue. None of what petrol diluted gets put back by it — and afterwards, that tank still holds the petrol.
The next start draws petrol back round the pump from your lines and the fuel filter, where some of it ends up after your engine has run. That is why draining your tank yourself does not leave you sorted — a myth. And, a can of petrol filled by the kerbside is genuinely dangerous.
How it happens: petrol in a diesel
It's seldom carelessness, and no one does it on purpose. One way only, since of the nozzles: the smaller petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one generally won't fit a petrol car. That's how the forecourt makes it straightforward.
It happens when habit and your car stop matching. Hire cars, courtesy cars, and vehicles that are new to you. Two motors on one driveway, one petrol, one diesel. The pumps in a different order on a well-known forecourt. A rushed fill en route to Culham with a train to catch. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist accustomed to petrol: precisely when it happens. Add a back seat full of children, a phone call or rain, and habit takes over.
How to avoid petrol in a diesel on your next fill-up in Caldecott
- Green for unleaded and black for diesel is normal in the UK — but not on every forecourt. Trust the label on the petrol pump, not the colour.
- The first fill in a new vehicle is the time to check the filler flap — on it, or on the cap, plenty of motors state which fuel to use.
- Label the key. In a household with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember.
- "Diesel", out loud, before you lift the nozzle — every time a new or hired car gets its first tank. It seems silly. It does the trick.
- Tuck your phone away. This is an easy mistake to make whilst you're thinking about something else.
- Add-on devices exist for motors without one, and some diesels come with a filler that will not take a petrol nozzle. Helpful — but a backstop at best, never a reason to stop checking the label.
- As soon as you realise, stop: less petrol in your tank means a weaker mix. What to do next does not change, though — still don't crank it.
Already put petrol in a diesel around Caldecott?
Then the order of things is brief. Never start the vehicle, and don't switch the ignition on. The attendants at the forecourt — whether at Marcham Road Service Station itself or wherever you filled up — will usually help roll it clear of the pump if you ask. Next, 0333 366 0103. We'll ask what was put in, roughly how much, and if it's been run.
Say so if it was AdBlue rather than petrol: it is a different issue, with its own page for Caldecott, because AdBlue brings corrosion and deposits instead of lost lubrication.
Caldecott petrol in a diesel tasks: why one costs more than another
The four scenarios above are four separate jobs, so no single price for this would be honest. What moves the cost is chiefly which of them you are in. Next it's the ratio — how much petrol was put in against how much the tank holds — and after that where the vehicle is and whether our van can reach it safely.
That's why our technicians ask three queries before pricing rather than after: what was put in, how much, and whether it's run. Their replies are what change a range into one firm number.
About Caldecott, briefly
Caldecott is a suburban area in Oxfordshire, situated on the banks of the River Thames at an elevation of 54 metres. Caldecott lies approximately 6 miles south of Oxford and 51 miles west of London, with nearby places including Abingdon-on-Thames and Shippon. Caldecott has a population of around 8611 people, predominantly living in terraced housing. Caldecott is close to the village of Wildmoor, and its riverside setting makes it a notable part of the local landscape.
Fuel drain cover across Oxfordshire, Caldecott included
Caldecott waits in the OX postcode area, and the teams that answer petrol in diesel jobs there work the spots around it as well — Abingdon-on-Thames, Wildmoor and Shippon among them. No need to bring the car to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all places we drain.
Caldecott: still at the pump?
Then, you couldn't be in a better place. Keep it off. Phone.