Should You Worry? Petrol in a Diesel Car in High Town
Unstarted? Then less worried than you likely feel. Petrol resting in a diesel tank does nothing to your engine till something draws it through the system — the ignition priming the pump, the starter, or driving itself. So the truthful answer to the first question anyone around High Town asks, "have I wrecked it?", is generally no. Petrol in Diesel is who to call, with the motor left off, so it stays that way. Below, this page sets out what petrol really does inside a diesel, how far it might have gone, and how to stop it happening to you a second time.
Inside the motor: what petrol in a diesel does
Diesel does two jobs on its way through a motor. Before it burns, it protects — and then it burns. Your high-pressure pump and the injectors are built to very fine gaps, and your diesel passing through them is what stops those surfaces from grinding against one another.
Petrol does the first task badly and the second not at all. A pump running on a petrol mixture is wearing itself out, since petrol is runnier than diesel and takes away the protection your fuel system relies on. Petrol is also designed to resist igniting under compression — the reverse of what a diesel needs from its fuel — and that is where the rattling starts.
Put these together and the shape of the trouble is clear. The harm is done by movement, not by contact. Petrol in a tank is a fuel fault. Whatever a worn pump sheds goes on, borne by the fuel, into your injectors downstream, which is why a pump that has worked on that petrol is where a mechanical fault starts.
How bad is petrol in a diesel? Four scenarios we see around High Town
The best case there is: filled up, not once started. Just your tank has petrol in it, and so the job is clearing your tank and flushing your system where the vehicle stands. This situation can only really occur on a forecourt: anywhere else, your car got there by being driven.
A brief spell of running, or just the ignition on. With the system primed, your lines and filter already hold petrol that has come from the tank. Normally little more than clearing, rinsing and seeing to your filter, and so still straightforward.
Those few miles driven meant the pump working on fuel weakened by petrol throughout. Distance is only half of that; how hard it was driven counts just as much. Either way the work includes your tank, your lines, your filter and fresh fuel through the entire system. The school run to St John's Catholic Primary School, A Voluntary Academy is one thing. Any distance on the M54, under 10 miles from High Town, means the engine working hard throughout, and a run to Wolverhampton, under 15 miles away, makes a very different task too.
Driven till it protested. Rattling, a ragged idle, smoke, a throttle that has gone soft. The engine is telling you the fuel is no longer acting like diesel. Whether it's the verge on High Street, a lay-by or a side street, stop where you are and leave it. What goes first is still the fuel drain and flush-through, and that deals with it, with lasting damage very unusual when a car is pulled over soon.
Petrol in a diesel myths High Town drivers hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. A bigger tank of the same mix is all you get, because topping up removes nothing. Percentage is not how a diesel fuel system tolerates petrol, whatever that guidance assumes.
"Modern diesels can handle a little petrol" — a myth, and closer to the opposite. At higher pressure, through more precise parts: that is how a modern diesel handles its fuel, so the protection matters for more, not less.
The myth that catches motorists out: if it starts and drives, it must be unharmed. Any petrol engine fed diesel normally won't run, so the motorist stops and the harm stops with them. While your pump wears, a diesel fed petrol usually starts, ticks over and drives away as if nothing has happened. Running doesn't mean fine.
Myth: "Add some two-stroke oil and drive the vehicle home." It is an old workaround for a different problem. What petrol has diluted remains diluted, and that petrol stays in that tank regardless.
If the motor has been run, part of the petrol is in the fuel filter and your lines, not the tank — and the next start sends it right back through the pump. So the myth "drain your tank yourself and you're sorted" does not hold. On top of that, petrol drained into a can by the road is truly risky.
Why petrol in a diesel occurs so easily
On purpose? Never. Through carelessness? Seldom, if ever. The forecourt makes it simple: the petrol nozzle is the smaller of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle mostly won't go into a petrol motor at all. So the slip runs one way.
Routine and your car getting out of step is how it happens. A vehicle that is new to you — hired, on loan as a courtesy car, or just bought. Two vehicles on one drive, one petrol, one diesel. The pumps in a different order on a familiar forecourt. Racing for a train at Cosford and fuelling up en route. Years of petrol vehicles behind you, a diesel Renault Clio in front of you on the forecourt for its first tank — that's when. Throw in a back seat full of kids, a phone call or rain, and the hand wins.
Preventing petrol in a diesel next time you fill up in High Town
- Read the petrol pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on each forecourt. The label is what matters.
- Many cars state the fuel inside the filler flap or on the cap, and so check there on your first fill in any vehicle you do not know.
- Good intentions do less than a sticker or a fob in a vivid colour on your diesel's key when a home has one of each. So label it.
- It sounds silly and it does the trick: on your first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the petrol pump.
- Thinking about something else is when this becomes an easy mistake to make, so put the phone away then keep your mind on the pump.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to reject a petrol nozzle, and add-on devices are available for vehicles without one. They are a backstop, not a reason to stop checking the petrol pump.
- Less petrol makes a thinner mixture, so stop the moment you notice — while remembering that the next stage is unchanged. It is still not to fire it up.
Already put petrol in a diesel around High Town?
Then the order of things is short. Leave it unstarted, with the ignition switched off as well. Yet on the forecourt, at Esso or anywhere else? Ask the staff to help you push the vehicle clear of the pump. Then ring 0333 366 0103 and tell us what got in, about how much, and whether it has run.
If it was AdBlue and not petrol, say so. That is a separate problem — corrosion and deposits and not lost lubrication — and it has its own page for High Town.
One petrol in a diesel job around High Town costs more than another. Why?
There's no honest single quote for this, because the four scenarios above are four different tasks. Mostly, your cost moves with which situation you are in. The ratio counts next, meaning how much of the tank is petrol, followed by the location of the car and whether reaching it is safe for a technician.
Before any quote, not after, we ask three questions: the fuel that went in, the volume, and if it's run. That is why. With those replies, you get a straight figure rather than a range.
About High Town and its setting
High Town is a suburban area in Shropshire, situated on the riverside at an elevation of 72 metres, with terraced housing being the predominant type of accommodation. High Town is located near several notable places, including Bridgnorth, Low Town, and Castle Hill, and is approximately 12.7 miles from Wolverhampton. High Town has a population of around 3470 residents, who enjoy a relatively quiet location despite being within commuting distance of larger cities. High Town is also some 120.6 miles from London, making it a potential base for those who need to travel to the capital,
Fuel drain cover across Shropshire, High Town included
Bridgnorth, Low Town and Castle Hill are among the spots around High Town that the same teams work, answering petrol in diesel call-outs across High Town's WV postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations our technicians work, and the car doesn't need to come to us.
High Town: still at the petrol pump?
The best spot there is, then — that is where you are. Keep it off. Phone.