Newtown: Petrol in a Diesel Car? How Worried to Be
If it hasn't been started, you can worry far less than you probably are. Till your ignition primes your pump, the starter cranks, or your vehicle is driven, petrol in a diesel tank simply waits there and does nothing. Which means the truthful reply to that first Newtown query — "have I wrecked it?" — normally no. Leave your engine off and call Petrol in Diesel — that keeps it that way. The remainder of this page sets out what petrol really does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
What petrol in a diesel does to your engine
Diesel does two tasks on its way through a motor. Before it ignites, it protects — then it ignites. What keeps the surfaces inside the high-pressure pump and the fuel injectors from wearing against each other is the diesel passing through them — they're made to extremely fine tolerances.
The second task petrol does not do at all, and the first it does badly. It's runnier than diesel and takes away the lubrication your fuel system depends on, and 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 reverse of what a diesel needs from its fuel. That is where the rattling comes from.
Seen together, they show the shape the trouble takes. Not contact but circulation is what causes the damage. Petrol in the tank is a fuel problem. The start of a mechanical one is a pump that has been labouring on that petrol — and whatever a worn pump sheds travels on with your fuel to your injectors beyond it.
Newtown, petrol in a diesel: four situations, from mild to serious
Filled up, and never started: no case is better. Being on a forecourt is what makes this the case: elsewhere, the car has been driven there to begin with. With that petrol kept inside your tank alone, it's drained and cleaned on the spot, and nothing more is needed.
Started for a moment, or only your ignition on. Once primed, the fuel system has pulled petrol from the tank up to the fuel filter and your lines. That is generally still a simple job — a drain, a flush, and your filter seen to.
A couple of miles driven, and your pump has spent every one of them working on diluted fuel. The work is your tank, the fuel lines, your filter and fresh fuel through the entire system, and how hard the car was driven matters as much as how far. Short trips, such as the school run to Mengham Infant School, are one thing. Very different once more: a trip to Portsmouth, under 5 miles away, or some mileage on the Waterlooville Bypass, under 5 miles from Newtown, where the engine never stopped working hard.
Driven on till it complained — knocking, smoke, a lumpy idle, a soft throttle. That is the engine telling you its fuel no longer is behaving like diesel. Stop wherever you are — the verge on Charleston Close, a lay-by, a side street — then leave the car there. A vehicle stopped soon very seldom has long-term damage, since the drain and the flush-through, which still come first, deal with it.
What Newtown people get told about petrol in a diesel — and the myths in it
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. Topping up takes out nothing; it gives you a bigger tank of the same mix. That advice assumes a diesel fuel system tolerates petrol by percentage. It doesn't.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. Protection matters more on modern diesels, not less, because their fuel runs through smaller parts at higher pressure.
One myth that catches drivers out: if it starts and drives, it must be unharmed. Any petrol engine fed diesel generally won't run, so the driver stops and the damage stops with them. While your pump grinds, a diesel fed petrol normally starts, idles and drives away as if nothing has happened. A running engine does not mean fine.
Not so: a two-stroke additive makes it safe to drive home. It was an old workaround, supposed for another problem. None of what petrol diluted gets put back by it — and afterwards, your tank still contains that petrol.
Once the motor has run, part of that petrol is in the filter and the lines, not that tank — and the next start pulls it straight back through the pump. So the myth "drain that tank yourself and you are sorted" does not stand up. It's also truly risky to drain petrol into a can at the roadside.
How does petrol in a diesel occur?
Carelessness is rarely the cause, and no one means to do it. A diesel nozzle generally won't go into a petrol motor, but the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake easy, and only in that direction.
When routine and the car stop matching, it takes place. A new vehicle, a hire car or a courtesy car. Two motors on one drive, one petrol, one diesel. Your usual forecourt, its pumps now in a different order. Rushing for a train at Fratton and filling up en route. Precisely the moment it happens: after years of driving petrol, someone fills a diesel Volkswagen Golf for the first time. Add a back seat full of children, a phone call or rain, and habit wins.
Newtown people: how to prevent petrol in a diesel next time
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, even if most usually do. Check the pump's label; the colour is just a hint.
- The first fill in a new motor is the time to check your filler flap — on it, or on the cap, many cars state which fuel to use.
- Good intentions do less than a sticker or a fob in a vivid colour on your diesel's key when a house has one of each. So label it.
- Before the nozzle comes off the petrol pump the first time you fill a hired or new car, say "diesel" aloud. Silly, perhaps, yet it does the trick.
- Whilst you're thinking about something else, this is an easy mistake to make — so put the phone away.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to reject a petrol nozzle, and add-on devices exist for vehicles without one. They are a backstop, not a reason to stop reading the petrol pump.
- As soon as you realise, stop: less petrol in your tank makes a weaker mixture. What to do next doesn't change, though — still do not fire it up.
Put petrol in a diesel around Newtown already?
Then, there's only a short order of things. Do not fire it up, and don't switch your ignition on. Still at the forecourt, at JET or anywhere else? Ask the attendants to help you push the car clear of the petrol pump. Then phone 0333 366 0103 and tell us what went in, about how much, and whether it has run.
If it was AdBlue instead of petrol, say so. That is a separate problem — corrosion and deposits and not lost protection — and it has its own page for Newtown.
One petrol in a diesel job in Newtown costs more than another. Why?
Four different jobs lie behind the four situations above — which is why there's no honest single quote. What moves your cost is mostly which of them you are in. Where the car is matters too, and whether a technician can safely reach it, after the share of petrol to what your tank takes.
That's why our engineers ask three questions before costing instead of after: what went in, how much, and if it's run. A range turns into a straight figure once those answers are in.
About Newtown
Newtown is a coastal suburban area in Hampshire, situated near the city of Portsmouth and close to several nearby places including West Town and Gable Head. Newtown sits at a low elevation of around 5 metres, reflecting its proximity to the sea. Newtown has a population of approximately 3161 residents, who mostly live in detached housing.
Newtown and Hampshire: where our fuel drain cover runs
Petrol in diesel call-outs around Newtown — part of the PO postcode area — go to vans that also cover the spots about it, West Town, Gable Head and Westfield among them. Our technicians drain wherever your vehicle is — your own drive, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
At the pump around Newtown, still?
In that case, you couldn't be in a better place. Keep it off. Call.