Porton: Petrol in a Diesel Car? How Worried to Be
Likely less than you are now — as long as no one has started the vehicle. Till the ignition primes the pump, your starter turns, or your car is driven, petrol in a diesel tank simply rests there and does no harm. Which means the truthful reply to that first Porton query — "have I wrecked it?" — usually no. Leave your engine off then call Petrol in Diesel — that keeps it that way. The remainder of this page sets out what petrol actually does to a diesel, how to tell 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 engine?
On its way through a motor, diesel does two jobs. Before it ignites, it protects — then it combusts. The high-pressure pump and your injectors are designed to extremely fine tolerances, and your diesel passing through them is what keeps those surfaces from grinding against each other.
Of those two tasks, petrol manages the first badly and the second not at all. The rattling comes from petrol being designed not to ignite when compressed, which is exactly the reverse of what a diesel needs. On top of that it is runnier than diesel, it strips out the protection the system depends on, and any pump running on that mixture is wearing itself.
Together, those make the shape of the issue clear. It's circulation that does the damage, not contact. Petrol in the tank is a fuel issue. Whatever a worn pump sheds travels on, borne by your fuel, into the fuel injectors downstream, which is why a pump that has worked on the petrol is where a mechanical issue starts.
How serious is petrol in a diesel? Four scenarios our engineers see in Porton
The best case there can be: filled up, not once started. Being on a forecourt is what makes this possible: elsewhere, your car has been driven there to begin with. With the petrol held in that tank alone, it is emptied and purged right where it stands, and nothing more is needed.
Ignition on, or started for a moment. Petrol has come out of your tank and reached your filter and your lines, because your system has been primed. Drain, flush, deal with the fuel filter: still normally easy.
Driven a few miles. Now your pump has spent those miles working on thinned fuel. The work is the tank, the lines, your filter and fresh fuel through the entire system, and how hard your car was driven matters as much as how far. The school run to St Nicholas Church of England Primary School is one matter. A run as far as Salisbury, under 5 miles away, is a very different task. So is any mileage on the M27, under 25 miles from Porton, where your engine has been labouring hard the whole time.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone ragged. What you are hearing is the motor reporting fuel that no longer acts like diesel. Stop wherever you are — the verge on Winterslow Road, a lay-by, a side street — then leave the car where it is. What comes first is still the fuel drain and flush, and that deals with it, with lasting damage very unusual if a vehicle is stopped quickly.
Petrol in a diesel myths Porton people hear
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 mixture. That guidance supposes a diesel fuel system handles petrol by percentage. It doesn't.
Myth: a modern diesel copes with a bit of petrol. If anything, the reverse. A modern diesel sends its fuel through finer components at higher pressure, which makes the protection count more, not less.
One myth that catches drivers off guard: if it starts and drives, it must be unharmed. Diesel in a petrol motor generally means a motor that will not run: the driver stops, and so does the damage. While your pump wears, a diesel fed petrol normally starts, ticks over and drives away as though nothing has happened. Being able to run is not proof of being fine.
An old workaround for a separate fault is behind this one. Myth: "Add some two-stroke oil and drive the car home." None of what petrol weakened is put back by it — and afterwards, the tank still holds the petrol.
If the motor has been run, part of that petrol is in your filter and the fuel lines, not the tank — and the next start pulls it right back through the pump. So the myth "drain the tank yourself and you are sorted" does not hold. Emptying petrol into a can by the roadside is also genuinely risky.
Why petrol in a diesel occurs at all
On purpose? Never. Through carelessness? Rarely, if ever. One way only, because of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, whereas the diesel one mostly will not fit a petrol car. That's how the forecourt makes it easy.
The moment routine stops matching your car is the moment it happens. Hire cars, courtesy cars, and motors that are new to you. Households running one of each, petrol and diesel. Your ordinary forecourt, its pumps now in a different order. Racing for a train at Salisbury and filling up en route. Precisely the moment it occurs: after years of driving petrol, someone fills a diesel Renault Megane for the first time. With rain, a call arriving, or children to deal with, the hand simply does what it has always done.
Avoiding petrol in a diesel next time you fill up in Porton
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, but not on each forecourt. The label is what matters.
- Check the filler flap. Plenty of motors state the fuel type inside the flap or on the cap. Look at it on your first fill in any car you do not know.
- Label the key. In a home with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the petrol pump. It sounds daft and it does the trick.
- Thinking about something else is when this becomes an easy mistake to make, and so put your phone away then keep your mind on the petrol pump.
- Add-on devices are available for vehicles without one, and some diesels are built with a filler that won't accept a petrol nozzle. Useful — but a backstop only, never a reason to stop checking the label.
- Less petrol means a thinner mixture, so stop the moment you realise — though remembering that your next step is unchanged. It is still not to crank it.
Put petrol in a diesel around Porton already?
The order of things is brief, then. Starting it is out, and so is turning on your ignition. The attendants on the forecourt — whether at Murco itself or wherever you filled up — will normally help push it away from the pump if you ask. Then call 0333 366 0103 and tell us what was put in, about how much, and whether it has run.
Say so if it was AdBlue rather than petrol: it is a separate issue, with its own page for Porton, because AdBlue brings corrosion and deposits rather than lost lubrication.
One petrol in a diesel job around Porton costs more than another. Why?
An honest single quote does not exist here: four scenarios, four separate tasks. What moves the cost is mostly which of them you're in. Where your car is counts too, and whether a technician can safely reach it, after the ratio of petrol to what your tank takes.
That is why we ask three queries before pricing instead of after: what got in, how much, and whether it's run. A range turns into a straight figure when those replies are in.
About Porton itself
Porton is a village in Wiltshire, situated on the banks of the River Avon at an elevation of around 65 metres. Porton lies near the city of Salisbury, approximately 4.9 miles to the northwest, and is surrounded by smaller settlements like Gomeldon and its subdivisions. Porton has a population of around 1188 people, predominantly living in detached houses. Porton is located about 74.1 miles west of London, in the South West region of England.
Porton and Wiltshire: where our fuel drain cover runs
Gomeldon, East Gomeldon and West Gomeldon are among the locations near Porton that the same vans work, answering petrol in diesel call-outs across Porton's SP postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all places our technicians work, and the car doesn't need to come to us.
Still at the pump around Porton?
No position is better: that's where you now are. Ring, and keep it turned off.