Holloway: Petrol in a Diesel Car? How Worried to Be
Less than you likely are, if it hasn't been started. "Have I ruined it?" is the first question anyone around Holloway asks, and the truthful answer is generally no, since petrol resting in a diesel tank harms nothing till it is dragged through the fuel system — by ignition priming, by your starter, or by driving. Petrol in Diesel is who to phone, with your engine left off, and so it remains that way. The remainder of this page sets out what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
Your engine and petrol in a diesel: what happens
On its way through a motor, diesel has two jobs. It lubricates first, and after that does it burn. Designed to very fine gaps, your injectors and the pump depend on your diesel flowing through them to stop their surfaces wearing against one another.
Poorly at the first, not at all at the second: that's petrol. Being less viscous than diesel, petrol strips out the protection a fuel system needs, leaving a pump running on that mixture wearing itself. It's also made to resist igniting under compression — the opposite of what a diesel needs — which is where you get the clattering.
Together, those leave the shape of the trouble clear. Contact does not do the harm — movement does. Any tank with petrol in it is a fuel problem. Once your pump has been working on that petrol, a mechanical issue has started: whatever is shed by a pump that is grinding travels onward to the injectors with your fuel.
How bad is petrol in a diesel? Four situations we see in Holloway
Filled up, never started. The best case there can be. Being on a forecourt is what makes this the case: elsewhere, your car has been driven there to begin with. With that petrol kept in that tank alone, it's drained and flushed right where it stands, and nothing more is needed.
A brief spell of running, or just your ignition on. The system has been primed, so petrol has left the tank and got to your filter and the lines. Normally nothing more than emptying, purging and seeing to your filter, and so still easy.
A couple of miles driven, and your pump has spent each of them working on diluted fuel. Distance is only half of it; how hard it was driven matters just as much. Either way this work includes the tank, the lines, your filter and clean fuel through the whole system. Driving the kids to Lea Primary School is one sort of trip. Any distance on the M1, under 10 miles from Holloway, means the engine working hard throughout, and a run to Derby, under 15 miles away, makes a very different task too.
Driven on till it protested — clattering, smoke, a lumpy idle, a dead throttle. The engine is telling you your fuel is no longer acting like diesel. Leave it wherever it stops: a lay-by, a side street, the verge on Little London. Lasting damage is very rare when a car is stopped early, and the fuel drain and flush that still come first sort it out.
Myths Holloway drivers hear about petrol in a diesel
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing is removed by topping up — you're left with a fuller tank, still the same mixture. The idea behind that advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the opposite. A modern diesel sends its fuel through finer components at higher pressure, which makes the lubrication matter more, not less.
Myth: "If it starts and drives, there is no harm done." This is the one that catches motorists. Feed diesel to a petrol engine and it usually will not run, so the driver stops — and the damage stops with them. Feed petrol to a diesel and it usually fires up, idles and drives away as if nothing has happened — all while its pump is wearing. A running engine does not mean fine.
Not so: a two-stroke additive lets you to drive home. It was an old workaround, meant for another problem. It doesn't put back what petrol has thinned, and the petrol is still inside your tank afterwards.
The next start sends petrol back round your pump out of your lines and the filter, where some of it sits after the engine has been run. That is why draining the tank yourself does not leave you sorted — a myth. Emptying petrol into a can by the kerbside is also really dangerous.
How does petrol in a diesel occur?
On purpose? Never. Through carelessness? Rarely, if ever. The forecourt makes it easy: the petrol nozzle is the narrower of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle generally won't go into a petrol motor at all. So the mistake runs one way.
It occurs when routine and the vehicle stop matching. Any motor that's new to you — a hire car, on loan as a courtesy car, or brand new. Two cars on one drive, one petrol, one diesel. A well-known forecourt with the pumps in a different order. Racing for a train at Cromford and filling up en route. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is exactly the moment it happens. Throw in a back seat full of kids, a phone call or rain, and the hand takes over.
Preventing petrol in a diesel next time you fill up in Holloway
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on every forecourt. The label is what counts.
- Many motors state the fuel inside your filler flap or on the cap, so check there on your first fill in any motor you do not know.
- One of each in the household? Mark your key to the diesel — a bright fob, a sticker — because meaning to remember isn't enough.
- Say it before you lift it. On the 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, so tuck your phone away then keep your mind on the pump.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to refuse a petrol nozzle, and aftermarket devices are available for the remainder. Treat it as a safety net, then keep checking the pump.
- As soon as you realise, stop: less petrol inside your tank makes a thinner mixture. What to do next does not change, though — still do not start it.
Holloway: already put petrol in a diesel?
The order of things is brief, then. Leave it unstarted, with your ignition switched off too. If you're still on the forecourt — Murco or anywhere else — ask the attendants to help you roll the car away from the petrol pump. Then phone 0333 366 0103 and tell us what got in, roughly how much, and whether it has run.
Corrosion and deposits form the problem with AdBlue, where petrol brings lost lubrication. So if it was AdBlue, say so — and read its own Holloway page.
What makes one Holloway petrol in a diesel task cost more than the next
Four different jobs lie behind the four situations above — which is why there's no fair single price. What moves your cost is mostly which of them you're in. Beyond that it is the proportion — how much petrol got in against how much that tank takes — and then where the car is and whether a van can get to it safely.
Three questions come first, before quoting, rather than after — what got in, how much, has it run — and that is the reason. Those answers are what turn a range into one firm number.
About Holloway, for a moment
Holloway is a village in Derbyshire, situated on the riverside in the East Midlands region of England. Holloway has a population of around 783 people and is characterized by semi-detached housing. Holloway sits at an elevation of 159 metres, approximately 12.6 miles from Derby and 125 miles from London. Holloway is near other places such as Lea, High Peak Junction, and Dethick.
Across Derbyshire and around Holloway: fuel drain cover
Holloway waits in the DE postcode area, and the teams that answer petrol in diesel call-outs there work the places around it as well — Lea, High Peak Junction and Dethick among them. Our technicians drain where the vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
In Holloway and still at the petrol pump?
Then you are in the best place there can be. Keep it off. Call.