Chew Magna: Petrol in a Diesel Car? How Worried to Be
Likely less than you are now — provided no one has started the vehicle. Petrol sitting in a diesel tank does nothing to the motor till something pulls it through your fuel system — the ignition priming the pump, the starter, or driving on its own. So the honest answer to the first query everyone around Chew Magna asks, "have I ruined it?", is usually no. Leave your motor off then call Petrol in Diesel — that is how you keep it like that. What petrol really does to a diesel, how to judge how far it has travelled, and how to stop it from happening a second time: that is the remainder of this page.
What petrol in a diesel does to the motor
Passing through a motor, diesel does two things at once. Before it combusts, it lubricates — and then it burns. Very fine clearances go into the injectors and the high-pressure fuel pump, and only your diesel running through keeps their surfaces from grinding together.
Petrol handles the first task badly and the second not at all. It's runnier than diesel and removes the protection the fuel 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 is where the rattling comes from.
The shape of the trouble is plain when you put those together. Not contact but circulation is what does the damage. Petrol in the tank is a fuel fault. A pump that has been running on that petrol is the start of a mechanical one, and whatever a worn pump sheds travels on with your fuel to the fuel injectors further on.
Petrol in a diesel in Chew Magna: how bad is it? Four cases
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 that petrol kept inside the tank alone, it's cleared and rinsed right where it stands, and nothing more is needed.
A moment's running, or just your ignition on. Once primed, the fuel system has pulled petrol out of that tank as far as the fuel filter and the fuel lines. Still generally simple: drain, flush, and the filter seen to.
Those few miles driven meant your pump labouring on fuel thinned by petrol the whole way. Tank, lines, filter, then clean fuel put through the whole circuit: that's this work, and the way the car was driven counts as much as the miles. Short trips, such as the school run to Chew Magna Primary School, are one matter. Any mileage on the M32, under 10 miles from Chew Magna, means your engine has worked hard throughout, and a run to Bristol, under 10 miles away, makes a very different job as well.
Driven until it complained. Knocking, a ragged idle, smoke, a throttle that has gone soft. What you are hearing is your motor signalling fuel that no longer acts like diesel. Stop where you are — on the verge on South Parade, at the kerb, down a side road — and do not move it. Lasting damage is very uncommon when a car is pulled over soon, and the drain and flush-through that still go first sort it out.
What Chew Magna motorists get told about petrol in a diesel — and the myths in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." Topping up takes out nothing; it gives you a fuller tank of the same mix. A diesel fuel system does not accept petrol by percentage in the way that guidance supposes.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the reverse. At higher pressure, through finer parts: that's how a current diesel handles its fuel, and so the lubrication matters more, not less.
"It starts, it drives, and so no harm done" — the myth that trips up more drivers than any other. Any petrol engine fed diesel usually won't run, so the driver stops and the damage stops with them. A diesel fed petrol normally starts, idles and drives away as though nothing has happened, while the pump wears. A running engine does not mean fine.
Myth: "Add some two-stroke oil and drive the car home." It's an outdated fix for a separate problem. It doesn't put back what petrol has weakened, and the petrol is still inside that tank later.
The next start sends petrol back round your pump out of the fuel lines and the fuel filter, where some of it ends up after the motor has been run. That is why draining your tank yourself does not sort it — a myth. It is also genuinely risky to drain petrol into a can by the kerbside.
Why petrol in a diesel takes place at all
Carelessness is rarely the cause, and no one means to do it. One way only, because of the nozzles: the smaller petrol one slides inside a diesel filler with almost no resistance, while the diesel one generally will not fit a petrol vehicle. That's how the forecourt makes it straightforward.
The moment routine stops matching the vehicle is the moment it happens. Courtesy car, hire car, or a car that is brand new. Households running one of each, petrol and diesel. A forecourt you know, only with its pumps laid out differently. A train to catch, and a hurried fill en route to Parson Street. A new-to-you diesel Renault Megane, its first fuelling, and a motorist accustomed to petrol: exactly when it takes place. With rain, a call arriving, or a car full of children to deal with, your hand just does what it always has.
Next time you fill up in Chew Magna: avoiding petrol in a diesel
- Check the pump, not the colour. In the UK unleaded handles are generally green and diesel black, but not on every forecourt. The label is what counts.
- Plenty of motors state the fuel type inside the filler flap or on the cap, and so check it on your first fill in any car you don't know.
- A coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember, for a home with one of each.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the pump. It seems silly and it works.
- Mistakes like this are straightforward to make whilst your mind is on something else, and so the phone goes away.
- 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 safety net, and keep reading the pump.
- Stop as soon as you realise. Less petrol in that tank means a weaker blend. It doesn't change what to do next, which is still not to start the car.
Put petrol in a diesel around Chew Magna already?
In that case, there's only a short order of things. Do not switch the ignition on, and do not start it. Still at the forecourt, at Esso or anywhere else? Ask the staff to help you push the car away from the petrol pump. Then call 0333 366 0103 and tell us what went in, about how much, and whether it has run.
Say so if it was AdBlue instead of petrol: it is a different problem, with its own page for Chew Magna, because AdBlue brings corrosion and deposits rather than lost protection.
Chew Magna petrol in a diesel tasks: why one costs more than another
Four separate tasks lie behind the four scenarios above — which is why there's no honest single price. Mostly, the cost shifts with which situation you are in. Beyond that it's the ratio — how much petrol got in against how much your tank holds — and then where the car is and whether our van can reach it safely.
What got in, how much, and whether it's run — three questions our engineers ask before quoting, not after, for exactly that reason. Those replies turn a range into a straight figure.
About Chew Magna
Chew Magna is a village situated on the River Chew in Somerset, with a mix of old and new buildings, including many detached houses. Chew Magna lies close to the cities of Bristol and Bath, and its riverside setting gives it a distinctive character. Chew Magna has a population of around 1249 people and is surrounded by other small villages such as Moorledge and Chew Stoke. Chew Magna is located about 6 miles from Bristol and 107 miles from London.
Chew Magna and Somerset: where our fuel drain cover reaches
Petrol in diesel call-outs around Chew Magna — part of the BS postcode area — go to vans that also cover the locations around it, Moorledge, Littleton and Chew Stoke among them. A forecourt, a supermarket car park, a lay-by or your own drive are all spots we work, and the car doesn't need to move to us.
Chew Magna: still at the petrol pump?
Then you are in the best spot there is. Leave it turned off, and ring.