Maw Green: Petrol in a Diesel Car? How Worried to Be
If it has not been started, you can worry far less than you likely are. Petrol resting in a diesel tank does nothing to your engine until something draws it through the fuel system — the ignition priming the pump, your starter, or the drive on its own. So the honest answer to the first question everyone in Maw Green asks, "have I ruined it?", is usually no. Keep it that way: leave your motor off and ring Petrol in Diesel. The remainder of this page explains what petrol actually 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.
Petrol in a diesel: what does it do to the motor?
Diesel does two jobs on its way through an engine. It protects first, and after that does it burn. Extremely fine clearances are built into your injectors and the high-pressure fuel pump, and just your diesel running through keeps those surfaces from grinding together.
Petrol handles the first task badly and the second not at all. It is thinner than diesel and takes away the lubrication your fuel system hinges on, so a pump running on a petrol blend is a pump wearing itself. And petrol is made to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That's where the knocking comes from.
Put those together and the shape of the issue is clear. Not contact but circulation is what does the damage. A tank with petrol in it is a fuel problem. A pump that has been labouring on that petrol is the start of a mechanical one, and whatever a worn pump sheds travels on with the fuel to the fuel injectors further on.
Four scenarios our engineers see around Maw Green: how bad is petrol in a diesel?
Fuelled but never started — as good as it gets. That petrol is inside that tank and just the tank, and the job is a drain and a flush where the vehicle sits. This is the one scenario that can only truly occur at a forecourt, since anywhere else the vehicle has been driven to get there.
Ignition on, or started for a moment. Petrol has left that tank and reached your filter and your lines, since your system has been primed. Normally little more than clearing, cleaning and seeing to the filter, and so still simple.
The pump has worked a couple of miles on thinned fuel — that is what driving the car meant. Tank, lines, filter, then clean fuel run through the entire circuit: that's this work, and the way the car was driven counts as much as the mileage. Short trips, such as the school run to Monks Coppenhall Academy, are one matter. Any distance on the M6, under 5 miles from Maw Green, means your engine working hard throughout, and a run to Stoke-on-Trent, under 15 miles away, makes a very different task as well.
Driven on till it protested — clattering, smoke, a lumpy idle, a soft throttle. The engine is telling you the fuel is no longer acting like diesel. Stop wherever you are — the verge on Green Field Way, a lay-by, a side street — and leave it where it is. The drain and flush still go first, and they sort it out: when a vehicle is stopped quickly, permanent damage is very uncommon.
Petrol in a diesel stories Maw Green motorists hear
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Nothing is removed by topping up — you are left with a bigger tank, still the same mixture. Percentage is not how a diesel fuel system tolerates petrol, whatever that guidance assumes.
Myth: a current diesel copes with a bit of petrol. If anything, the opposite. At higher pressure, through finer components: that's how a newer diesel handles its fuel, and so the protection counts for more, not less.
Myth: "If it starts and drives, there's no damage done." This is the one that catches people. Feed diesel to a petrol engine and it generally won't run, so the driver stops — and the damage stops with them. Whilst your pump wears, a diesel fed petrol normally starts, idles and drives away as though nothing has happened. Being able to run isn't proof of being fine.
Myth: a two-stroke additive lets you to drive home. It was an old workaround, meant for another problem. None of what petrol weakened is put back by it — and afterwards, your tank still holds that petrol.
The next start draws petrol back round the pump out of your lines and your filter, where some of it sits once the motor has run. That's why draining your tank yourself doesn't sort it — a myth. Clearing petrol into a can at the kerbside is also genuinely hazardous.
How it happens: petrol in a diesel
Carelessness is seldom the cause, and no one means to do it. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slips into a diesel filler with almost no resistance, whilst a diesel nozzle generally won't go into a petrol vehicle at all. So the error runs one way.
It happens when routine and the vehicle stop matching. A vehicle that is new to you — a hire car, on loan as a courtesy car, or just bought. Households running one of each, petrol and diesel. A forecourt you know, but with its pumps laid out differently. A hurried fill on the way to Crewe with a train to catch. Years of petrol cars behind you, a diesel BMW 3 Series in front of you on the forecourt for its first tank — that's when. Throw in a back seat full of children, a phone call or rain, and the hand wins.
Next time you fill up around Maw Green: avoiding petrol in a diesel
- Green for unleaded and black for diesel is usual in the UK — yet not on each forecourt. Go by the label on the petrol pump, not the colour.
- Check your filler flap. Plenty of vehicles state the fuel type inside the flap or on the cap. Look at it on your first fill in a vehicle you don't know.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of intending to remember, in a household with one of each.
- It sounds silly and it does the trick: on your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the pump.
- Tuck the phone away. This is an easy mistake to make whilst you're thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler designed to refuse a petrol nozzle, and aftermarket devices exist for the rest. Count it as a backstop, and keep reading the pump.
- The moment you realise, stop: less petrol inside your tank makes a thinner mix. What to do next doesn't change, though — still do not crank it.
Petrol already in a diesel in Maw Green? Begin here
Short and simple, then, is the order of things. Don't turn your ignition on, and don't crank it. If you're still at the forecourt — Shell or anywhere else — ask the attendants to help you push it clear of the petrol pump. Then ring 0333 366 0103 and tell us what was put in, about how much, and whether it's run.
Say so if it was AdBlue rather than petrol: it is a different issue, with its own page for Maw Green, since AdBlue brings corrosion and deposits rather than lost protection.
Why one petrol in a diesel job around Maw Green costs more than another
The four scenarios above are four different tasks, so no single quote for this would be honest. Mostly, your cost shifts with which situation you're in. Beyond that it's the proportion — how much petrol went in against how much the tank takes — and after that where the vehicle is and whether a van can get to it safely.
That's why our engineers ask three questions before quoting rather than after: what went in, how much, and if it's run. A range becomes a straight figure once the replies are in.
About Maw Green
Maw Green is a suburban area in Cheshire, situated near the River Trent and characterised by semi-detached housing. Maw Green lies close to the nearby places of Coppenhall, Sydney, and Coppenhall Moss, and is approximately 12 miles from Stoke-on-Trent. Maw Green has a population of around 3960 residents and is located at an elevation of 54 metres above sea level. Maw Green is also relatively distant from London, being around 147 miles away.
Across Cheshire and in Maw Green: fuel drain cover
Maw Green sits in the CW postcode area, and the teams that answer petrol in diesel call-outs there work the spots around it as well — Coppenhall, Sydney and Coppenhall Moss among them. No need to move your car to us. Forecourts, supermarket car parks, lay-bys and your own drive are all locations where we work.
In Maw Green and still at the pump?
The best position there is, then — that's where you are. Leave it switched off, and ring.