Town End: Petrol in a Diesel Car? How Worried to Be
Not started? Then less anxious than you likely feel. Until your ignition primes the pump, the starter turns, or the vehicle is driven, petrol in a diesel tank simply sits there and does no harm. Which makes the truthful reply to that first Town End query — "have I ruined it?" — normally no. Keep it like that: leave the engine off and call Petrol in Diesel. The rest 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 does not happen to you again.
Inside the engine: what petrol in a diesel does
Two tasks fall to diesel on its route through a motor. It lubricates to begin with, and only then does it burn. What keeps the surfaces inside the high-pressure fuel pump and your injectors from grinding against one another is your diesel flowing through them — they are designed to very fine clearances.
Of these two tasks, petrol handles the first poorly and the second not at all. The knocking 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 thinner than diesel, it strips away the lubrication the fuel system rests on, and any pump running on such a blend is wearing itself.
Together, those leave the shape of the problem plain. The harm is done by movement, not by contact. Where that petrol is only inside your tank, it's an issue of fuel, nothing more. A pump that has been running on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with the fuel to your injectors further on.
How bad is petrol in a diesel? Four situations our engineers see in Town End
The best case there is: filled up, not once started. The petrol is inside that tank and only your tank, and the task is a drain and a flush where the car sits. This is the one scenario that can only truly occur at a forecourt, because anywhere else the vehicle has been driven to get there.
Ignition on, or started for a moment. With the system primed, your lines and filter already contain petrol that has come from that tank. That's normally still a straightforward job — a drain, a flush, and the fuel filter seen to.
The pump has worked a couple of miles on diluted fuel — that is what driving it meant. How hard your car was driven matters as much as how far, and the work covers the tank, the lines, the fuel filter and clean fuel through the whole circuit. Driving the children to Shooter's Grove Primary School is one kind of trip. Driving as far as Sheffield, under 3 miles away, makes a very different task — as does any mileage on the M1, under 10 miles from Town End, with the motor working hard all the way.
Driven till it complained. Clattering, an uneven idle, smoke, a throttle that has gone soft. That is the motor telling you its fuel has stopped acting like diesel. Leave it where it stops: a lay-by, a quiet street, the verge on Oldfield Road. What comes first is still the fuel drain and flush, and that takes care of it, with lasting damage very unusual if a vehicle is pulled over quickly.
Town End motorists and that petrol in a diesel myths they hear
"Top it up the rest of the way with diesel and it will be fine" — a myth. It will not. Nothing is removed when you top up — your tank just carries more of the same mixture. That advice supposes a diesel fuel system tolerates petrol by percentage. It doesn't.
Myth: a modern diesel copes with a bit of petrol. Rather, the opposite. Protection counts more on modern diesels, not less, because their fuel passes through more precise parts at higher pressure.
One myth that catches drivers off guard: if it starts and drives, it must be unharmed. A petrol motor fed diesel generally won't run, and so the driver stops and the damage stops with them. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually does; meanwhile your pump grinds. Running is not the same as fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a separate problem. That petrol is still in the tank afterwards, and what it has weakened is not put back.
"Drain it yourself and you're sorted" — a myth, because after it has been running some petrol sits in the fuel filter and lines, ready to go straight back through your pump at your next start. Draining petrol into a can at the roadside is also truly risky.
Why petrol in a diesel happens at all
On purpose? Never. Through carelessness? Rarely, if ever. The petrol nozzle is the smaller of the two and slides into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol car at all. The forecourt makes it easy, and the mistake runs one way.
It occurs when habit and the vehicle stop matching. Any motor that's new to you — hired, on loan as a courtesy car, or brand new. One petrol and one diesel on the driveway of the same household. A familiar forecourt with the pumps in a different order. A train to catch, and a rushed fill on the way to Sheffield. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist used to petrol: exactly when it happens. The hand does what it has always done once you add rain, a phone call or a back seat full of children.
Preventing petrol in a diesel next time you fill up in Town End
- Read the pump, not the colour. In the UK unleaded handles are usually green and diesel black, but not on every forecourt. The label is what counts.
- The first fill in an unfamiliar car is the time to check the filler flap — on it, or on the cap, many motors state the fuel they take.
- Good intentions count for 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" out loud before you take the nozzle off the pump.
- Thinking about something else is when this becomes an easy mistake to make, so tuck your phone away and keep your mind on the petrol pump.
- Add-on devices exist for vehicles without one, and some diesels are built with a filler that will not accept a petrol nozzle. Useful — but a safety net at best, never a reason to stop checking the label.
- Stop as soon as you notice. Less petrol in your tank makes a thinner mixture. It doesn't change what to do next, which is still not to fire it up.
Put petrol in a diesel in Town End already?
Short and simple, then, is the order of things. Do not turn your ignition on, and don't fire it up. The attendants at the forecourt — whether at JET itself or wherever you filled up — will normally help roll it clear of the petrol pump if you ask. Then phone 0333 366 0103 and tell us what went in, roughly how much, and whether it has run.
Corrosion and deposits are the problem with AdBlue, whereas petrol brings lost protection. So if it was AdBlue, say so — and see its own Town End page.
Why one petrol in a diesel job in Town End costs more than another
The four scenarios above are four separate jobs, so no single quote for this would be fair. Which of them you are in is chiefly what moves the cost. Two things come after that: the petrol that was put in as a share of what that tank holds, then the spot the car is in and whether a van can reach it safely.
What got in, how much, and whether it's run — three queries we ask before quoting, not after, for precisely that reason. With the replies, you get a straight figure rather than a range.
About Town End itself
Town End is a suburban area situated on the outskirts of Sheffield in South Yorkshire, with a riverside setting that offers scenic views. Town End has a mix of semi-detached housing and is located near other residential areas such as Liberty Hill and Stannington. Town End sits at an elevation of 186 metres, providing a vantage point over the surrounding landscape. Town End is close to the city of Sheffield, being only 2.7 miles away from the city centre.
Town End and South Yorkshire: where our fuel drain cover runs
Liberty Hill, Stannington and Park Head are among the places around Town End that the same vans work, answering petrol in diesel jobs across Town End's S postcode area. We drain wherever the vehicle is — your own drive, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
Still at the petrol pump in Town End?
Nothing beats it: that is where you now are. Call, and keep it turned off.