Dog and Gun: Petrol in a Diesel Car? How Worried to Be
Likely less than you are now — as long as no one has started it. Everyone around Dog and Gun starts with "have I wrecked it?", and the fair answer is generally no: petrol left in the tank of any diesel remains harmless until priming, cranking or driving draws it into your fuel system. Petrol in Diesel is who to phone, with your motor kept off, so it remains that way. What petrol really does to a diesel, how to gauge how far it has travelled, and how to keep it from happening again: that's the remainder of this page.
The motor and petrol in a diesel: what happens
Passing through an engine, diesel is doing two things at the same time. It combusts, and before it combusts it lubricates. Designed to very fine clearances, the fuel injectors and the pump rely on your diesel moving through them to keep their surfaces from wearing against one another.
Petrol handles the first job badly and the second not at all. The clattering comes from petrol being designed 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 your system rests on, and any pump working on such a mixture is wearing itself.
Together, those leave the shape of the problem clear. Not contact but movement is what causes the harm. Any tank with petrol in it is a fuel problem. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with the fuel to the fuel injectors downstream.
How bad is petrol in a diesel? Four scenarios our technicians see around Dog and Gun
Filled up, and never started: nothing beats it. At a forecourt, and truly only there, that petrol is still limited to that tank — because everywhere else your car was driven to reach it. The job is draining and cleaning on the spot.
Ignition on, or started for a second. Once primed, the fuel system has pulled petrol out of that tank as far as the fuel filter and the fuel lines. Still usually straightforward: drain, flush, and the filter seen to.
Driven a couple of miles. Now your pump has spent these miles working on thinned fuel. How hard the car was driven matters as much as how far, and the work takes in your tank, your lines, your filter and fresh fuel through the entire system. On the school run to Our Lady and St Philomena's Catholic Primary School, the distance is small. Driving as far as Liverpool, under 5 miles away, makes a very different task — as does any mileage on the M57, under 3 miles from Dog and Gun, with the motor running hard all the way.
Clattering, a ragged idle, smoke, a throttle gone soft: driven till it complained. The motor is telling you your fuel is no longer acting like diesel. Pull up where you are — on the verge on Oakgate Close, at the kerb, down a side road — and don't move it. A vehicle stopped soon very seldom has long-term damage, because the drain and the flush-through, which still go first, deal with it.
What Dog and Gun people get told about petrol in a diesel — and the stories in it
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Topping up removes nothing; it gives you a bigger tank of the same mixture. A diesel fuel system does not accept petrol by percentage in the way that advice supposes.
"Modern diesels can handle a little petrol" — a myth, and closer to the reverse. A newer diesel sends its fuel through finer parts at higher pressure, which makes the protection count more, not less.
"It starts, it drives, so no harm done" — the myth that trips up more motorists than any other. A petrol engine fed diesel normally will not run, and so the motorist stops and the damage stops with them. Whilst your pump grinds, a diesel fed petrol usually starts, ticks over and drives away as though nothing has happened. Running does not mean fine.
Not so: a two-stroke additive lets you to drive home. It is an old fix, meant for another fault. None of what petrol diluted gets put back by it — and later, the tank still contains that petrol.
The next start sends petrol back round the pump out of your lines and your filter, where some of that ends up once 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 roadside is also really hazardous.
How does petrol in a diesel occur?
Carelessness is seldom the cause, and nobody means to do it. The forecourt makes it simple: the petrol nozzle is the slimmer of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle generally won't go into a petrol motor at all. So the mistake runs one way.
The moment habit stops matching the vehicle is the moment it happens. Courtesy car, hire car, or a motor that's brand new. Two cars on one driveway, one petrol, one diesel. The pumps in a different order on a well-known forecourt. Fuelling up in a hurry on the way to Fazakerley, with a train to catch. The first fill-up in a diesel Renault Megane after years of driving petrol is precisely the moment it occurs. Add a back seat full of children, a phone call or rain, and the hand takes over.
How to prevent petrol in a diesel at your next fill-up in Dog and Gun
- A green handle for unleaded and black for diesel is usual in the UK — but not on each forecourt. Trust the label on the pump, not the colour.
- The first fill in a new motor is the time to check your filler flap — on it, or on the cap, plenty of vehicles state the fuel to use.
- Label the key. In a house with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of intending to remember.
- It sounds silly and it does the trick: on your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the pump.
- Tuck your phone away. This is an easy mistake to make whilst you are thinking about something else.
- Add-on devices exist for vehicles without one, and some diesels come with a filler that won't take a petrol nozzle. Useful — but a backstop at best, never a reason to stop checking the label.
- Less petrol means a weaker mixture, so stop as soon as you notice — while remembering that your next step is unchanged. It is still not to start the car.
Dog and Gun: already put petrol in a diesel?
Short and simple, then, is the order of things. Leave it unstarted, with the ignition switched off too. The staff on the forecourt — whether at EG On the Move itself or wherever you filled up — will usually help roll it clear of the petrol pump if you ask. Then ring 0333 366 0103 and tell us what went in, about how much, and if it's run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost protection, make it a separate issue — Dog and Gun has a page all for it.
One petrol in a diesel job in Dog and Gun costs more than another. Why?
There's no fair single price for this, because the four scenarios above are four separate jobs. Which of them you're in is chiefly what moves the cost. Where your car is matters too, and whether our van can safely get to it, after the share of petrol to what the tank holds.
Ahead of any quote, not after, we ask three queries: your fuel that was put in, the amount, and whether it has run. That is why. Given those answers, you get a straight figure rather than a range.
About Dog and Gun and its setting
Dog and Gun is a locality in Merseyside, situated on the riverside near Liverpool, with a mix of terraced housing and local amenities. Dog and Gun has a relatively low elevation of 23 metres, and its proximity to the city of Liverpool has influenced its development. Dog and Gun is close to nearby places such as Croxteth and Norris Green, and is part of the larger urban area surrounding Liverpool.
Fuel drain cover across Merseyside, Dog and Gun included
Croxteth, Gillmoss and Norris Green are among the places near Dog and Gun that the same teams work, answering petrol in diesel calls across Dog and Gun's L postcode area. You need not move your vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all places we drain.
Dog and Gun: still at the petrol pump?
Nothing beats it: that is where you are. Turned off it remains; then phone.