Dry Street: Petrol in a Diesel Car? How Worried to Be
Less than you likely are, if it hasn't been started. Petrol sitting in a diesel tank does nothing to your engine till something pulls it through your fuel system — the ignition priming your pump, the starter, or driving itself. So the truthful answer to the first question anyone in Dry Street asks, "have I wrecked it?", is generally no. To keep it that way, ring Petrol in Diesel then leave your engine switched off. Below, you will find what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you a second time.
Inside the motor: what petrol in a diesel really does
Two tasks fall to diesel on its journey round a motor. It lubricates first, and after that does it burn. Very fine tolerances are built into the fuel injectors and the high-pressure fuel pump, and just the diesel running through keeps those surfaces from grinding together.
Badly at the first, not at all at the second: that is petrol. A pump running on a petrol blend is wearing itself out, since petrol is runnier than diesel and strips out the lubrication the fuel system relies on. Petrol is also made to resist igniting under compression — the reverse of what a diesel wants from its fuel — and that's where any clattering starts.
Seen together, they show the shape the trouble takes. The damage is done by movement, not by contact. Petrol in the tank is a fuel fault. The beginning of a mechanical problem is a pump that has been working on that petrol — and whatever a worn pump sheds travels on with the fuel to the fuel injectors downstream.
How serious is petrol in a diesel? Four situations our engineers see in Dry Street
Filled but never started — the best it gets. Just your tank has petrol in it, and so the task is draining the tank and purging the fuel system where your car sits. This situation can only truly take place on a forecourt: anywhere else, the car got there by being driven.
The ignition switched on, or a brief start. Petrol has come out of that tank and got to the fuel filter and your lines, because your system has been primed. Still normally easy: drain, flush, and the fuel filter dealt with.
Driven a few miles. Now your pump has spent these miles labouring on weakened fuel. The work is the tank, the fuel lines, your filter and fresh fuel through the whole circuit, and how hard the vehicle was driven matters as much as how far. A school run to Chapel Hill Primary School & Nursery is one thing. A run as far as Southend-on-Sea, under 15 miles away, is a very different task. So is any mileage on the M25, under 10 miles from Dry Street, where the engine has been running hard the whole time.
Knocking, a ragged idle, smoke, a throttle gone soft: driven till it complained. The motor is telling you your fuel is no longer behaving like diesel. Leave it where it stops: a lay-by, a quiet street, the verge on Dry Street. What goes first is still the drain and flush-through, and that sorts it out, with long-term damage very unusual if a car is pulled over soon.
Stories Dry Street motorists hear about petrol in a diesel
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." A bigger tank of the same mixture is all it gives, because topping up removes nothing. A diesel fuel system doesn't tolerate petrol by percentage in the way that advice assumes.
If anything, the opposite holds. Myth: "A modern diesel can cope with a bit of petrol." More precise parts and higher pressure are how a modern diesel runs its fuel, and that makes the lubrication count more, not less.
Myth: "If it starts and drives, there is no damage done." This is the one that fools people. Diesel in a petrol motor generally means a motor that will not run: the driver stops, and so does the damage. Feed petrol to a diesel and it generally starts, ticks over and drives away like nothing happened — all while its pump is wearing. Being able to run is not proof of being fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a different fault. What petrol has weakened stays weakened, and the petrol remains inside your tank regardless.
If the engine has been run, part of that petrol is in the fuel filter and the fuel lines, not the tank — and the next start pulls it straight back through your pump. So the myth "drain your tank yourself and you are sorted" doesn't stand up. It's also genuinely hazardous to drain petrol into a can at the roadside.
Why petrol in a diesel takes place at all
Nobody does it on purpose, and it's seldom carelessness. The petrol nozzle is the narrower of the two and slides into a diesel filler with almost no resistance; a diesel nozzle generally will not go into a petrol vehicle at all. The forecourt makes it easy, and the error runs one way.
Habit and the vehicle getting out of step is how it occurs. A motor that's new to you — a hire car, on loan as a courtesy car, or just bought. Two vehicles on one driveway, one petrol, one diesel. The pumps in a different order on a familiar forecourt. Filling up in a rush on the way to Basildon, with a train to catch. Years of petrol vehicles behind you, a diesel Volkswagen Passat in front of you on the forecourt for its first tank — that's when. Throw in a back seat full of children, a phone call or rain, and habit wins.
How to prevent petrol in a diesel at your next fill-up in Dry Street
- A green handle for unleaded and black for diesel is normal in the UK — but not on every forecourt. Trust the label on the pump, not the colour.
- Plenty of vehicles state the fuel type inside the filler flap or on the cap, and so check it on your first fill in a car you do not know.
- Label the key. In a house with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember.
- 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.
- Tuck your phone away. This is an easy mistake to make while you are thinking about something else.
- Add-on devices are available for cars without one, and some diesels come with a filler that won't accept a petrol nozzle. Helpful — but a safety net only, never a reason to stop checking the label.
- The moment you notice, stop: less petrol in that tank makes a weaker mixture. What to do next doesn't change, though — still do not crank it.
Put petrol in a diesel in Dry Street already?
Short and simple, then, is the order of things. Don't fire it up, and do not turn your ignition on. Still at the forecourt, at Murco or anywhere else? Ask the staff to help you roll the car away from the petrol pump. Ring 0333 366 0103 next, with three answers — your fuel, the approximate quantity, and whether it has run.
Corrosion and deposits form the trouble with AdBlue, where petrol brings lost lubrication. So if it was AdBlue, say so — and read its own Dry Street page.
Dry Street petrol in a diesel tasks: why one costs more than another
There is no fair single price for this, since the four scenarios above are four separate tasks. What shifts the cost is chiefly which of them you're in. After that it's the share — how much petrol went in against how much that tank takes — and then where the vehicle is and whether a van can reach it safely.
Before any quote, not after, come three questions: the fuel that was put in, its quantity, and whether it has run. That is why. Those answers change a range into a straight figure.
About Dry Street, for a moment
Dry Street is a locality in Essex, situated inland at an elevation of around 68 metres, approximately 24.7 miles from London. Dry Street is characterized by its predominantly detached housing stock, reflecting the area's residential nature. Dry Street is close to several nearby places, including Westley Heights, Lee Chapel South, and Langdon Hills, and is about 11.5 miles from the city of Southend-on-Sea.
Across Essex and in Dry Street: fuel drain cover
Petrol in diesel call-outs around Dry Street — part of the SS postcode area — go to teams that likewise cover the places round it, Westley Heights, Lee Chapel South and Langdon Hills among them. The vehicle doesn't need to come to us: we drain on a forecourt, in a supermarket car park, in a lay-by or on your own drive.
Still at the petrol pump around Dry Street?
Then you are in the best place there can be. Call, and keep it turned off.