Holt: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less anxious than you probably are. Until the ignition primes the pump, your starter turns, or your car is driven, petrol in a diesel tank simply sits there and does nothing. Which means the truthful reply to the first Holt query — "have I ruined it?" — usually no. Petrol in Diesel is who to phone, with your engine kept off, and so it stays that way. Below, this page sets out what petrol actually does inside a diesel, how far it might have gone, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to the engine?
Two jobs fall to diesel on its journey round a motor. It protects to begin with, and after that does it burn. What stops the surfaces inside your high-pressure pump and the fuel injectors from grinding against each other is your diesel flowing through them — they are designed to very fine clearances.
Petrol handles the first task poorly and the second not at all. A pump running on a petrol mixture is wearing itself out, because petrol is runnier than diesel and strips out the protection your fuel system depends on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that is where any rattling starts.
Combined, those make the shape of the trouble clear. Not contact but movement is what causes the damage. Where the petrol is only inside your tank, it is a fault of fuel, nothing more. The beginning of a mechanical one is a pump that has been labouring on that petrol — and whatever a worn pump sheds travels on with your fuel to the fuel injectors downstream.
Petrol in a diesel in Holt: how serious is it? Four situations
Filled up, never started. The best case there can be. Just that tank has petrol in it, so the job is emptying that tank and flushing your system where the car sits. This scenario can only truly take place at a forecourt: anywhere else, your car got there by being driven.
Ignition on, or started for a moment. With the fuel system primed, the fuel lines and filter already contain petrol that has come from your tank. That is usually still a simple task — a drain, a flush, and your filter seen to.
Driven a few miles. Now your pump has spent these miles running on thinned fuel. Tank, lines, filter, then fresh fuel run through the entire circuit: that's the work, and the way the vehicle was driven matters as much as the miles. Short trips, like the school run to Holt Voluntary Controlled Primary School, are one matter. Any distance on the M4, under 15 miles from Holt, means the motor has worked hard throughout, and a run to Bath, under 10 miles away, makes a very different task too.
Driven on until it complained — clattering, smoke, a ragged idle, a soft throttle. What you are hearing is the motor signalling fuel that no longer behaves like diesel. Whether it's the verge on The Midlands, a lay-by or a side street, stop there then leave it. Lasting damage is very unusual when a vehicle is pulled over quickly, and the fuel drain and flush-through that still come first deal with it.
What Holt people get told about petrol in a diesel — and the myths in it
Myth: topping up to full with diesel makes it fine. It doesn't. A bigger tank of the same mix is all it gives, because topping up removes nothing. The idea behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
If anything, the reverse is true. Myth: "A modern diesel can cope with a bit of petrol." At higher pressure, through finer parts: that's how a current diesel handles its fuel, so the lubrication matters more, not less.
Myth: "If it starts and drives, there's no damage done." This is the one that catches people. Any petrol engine fed diesel normally won't run, and so the driver stops and the damage stops with them. A diesel fed petrol generally starts, ticks over and drives away as if nothing has happened, while the pump grinds. Being able to run isn't proof of being fine.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an outdated workaround for a separate problem. The petrol is still inside your tank after that, and what it has weakened is not put back.
"Drain it yourself and you're sorted" — a myth, since after it has been running some petrol lies in your filter and lines, waiting to go right back through your pump at your next start. And, a can of petrol drained by the roadside is genuinely dangerous.
How does petrol in a diesel happen?
On purpose? Never. Through carelessness? Seldom, if ever. One way only, since of the nozzles: the narrower petrol one slips 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 easy.
The moment routine stops matching the vehicle is the moment it happens. A car that's new to you — hired, on loan as a courtesy car, or brand new. Two motors on one drive, one petrol, one diesel. A familiar forecourt with the pumps in a different order. Rushing for a train outside Bradford-On-Avon and fuelling up en route. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist used to petrol: precisely when it takes place. Add a back seat full of children, a phone call or rain, and the hand wins.
Next time you fill up in Holt: preventing petrol in a diesel
- Green for unleaded and black for diesel is normal in the UK — but not on every forecourt. Go by the label on the petrol pump, not the colour.
- The first fill in a new motor is the time to check the filler flap — inside it, or on the cap, many motors state the fuel they take.
- One of each in the home? Label the key to the diesel — a coloured fob, a sticker — since intending to remember isn't enough.
- "Diesel", out loud, before you pick up the nozzle — each time a new or hired car gets its first tank. It sounds silly. It works.
- While you are thinking about something else, this is an easy mistake to make — so tuck the phone away.
- Some diesels have a filler built to reject a petrol nozzle, and devices you can add exist for motors without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop reading the pump.
- As soon as you realise, stop: less petrol inside your tank makes a thinner mixture. What to do next doesn't change, though — still don't start the vehicle.
Put petrol in a diesel around Holt already?
Short and simple, then, is the order of things. Never start the car, and don't turn the ignition on. Ask the attendants to help you push it clear of the pump if you are still on the forecourt, whether that's Texaco or somewhere else. Then phone 0333 366 0103 and tell us what went in, about how much, and if it has run.
Corrosion and deposits are the trouble with AdBlue, whereas petrol means lost protection. So if it was AdBlue, say so — and see its own Holt page.
Holt petrol in a diesel jobs: why one costs more than another
The four situations above are four different tasks, so no single quote for this would be fair. Chiefly, the cost moves with which situation you are in. Two things follow that: the petrol that went in as a proportion of what the tank holds, then the spot the vehicle is in and whether a technician can reach it safely.
What got in, how much, and if it's run — three queries our technicians ask before costing, not after, for precisely that reason. Those replies change a range into a straight figure.
About Holt and its setting
Holt is a village in Wiltshire, situated inland near the city of Bath, with Holt being close to several nearby places including Ham Green, Great Chalfield, and Staverton. Holt has a population of around 1052 people and is characterised by semi-detached housing. Holt sits at an elevation of 43 metres, relatively low compared to surrounding areas, and is located about 89.7 miles west of London.
Across Wiltshire and around Holt: fuel drain cover
Petrol in diesel calls around Holt — part of the BA postcode area — go to teams that likewise cover the spots round it, Ham Green, Great Chalfield and Staverton included. The car doesn't need to come to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Still at the pump around Holt?
Then you're in the best spot there can be. Ring, and leave it turned off.