How Worried Should You Be? Petrol in a Diesel Car in Porlock
If it hasn't been started, worry far less than you probably are. "Have I ruined it?" is the first question everyone in Porlock asks, and the truthful answer is normally no, because petrol left in a diesel tank harms nothing until it's drawn through the system — by ignition priming, by the starter, or by driving. Keep it that way: leave the engine off and call Petrol in Diesel. Keep reading for three things: the effect petrol has inside a diesel engine, the clues of how far it has got, and ways to make sure you don't do it again.
Inside the motor: what petrol in a diesel really does
On its way through an engine, diesel does two tasks. It protects first, and only then does it burn. Your high-pressure pump and your injectors are built to extremely fine clearances, and the diesel passing through them is what stops those surfaces from wearing down against one another.
The second task petrol doesn't do at all, and the first it does badly. The rattling comes from petrol being designed not to ignite when compressed, which is precisely the opposite of what a diesel needs. On top of that it is runnier than diesel, it strips out the lubrication the system hinges on, and any pump running on that mix is wearing itself.
Combined, those make the shape of the issue plain. Not contact but circulation is what does the harm. All a tank with petrol in it amounts to is a fuel issue. Whatever a worn pump sheds travels on, borne by your fuel, into the injectors downstream, which is why a pump that has worked on that petrol is where a mechanical fault starts.
Four situations our engineers see in Porlock: how bad is petrol in a diesel?
Fuelled but not once started — the best it gets. Just the tank has petrol in it, and so the job is clearing your tank and cleaning your system where the vehicle sits. This scenario can only truly happen on a forecourt: anywhere else, the car got there by being driven.
Your ignition turned on, or a brief start. Your system has been primed, and so petrol has left your tank and reached your filter and the lines. That's usually still a straightforward job — a drain, a flush, and your filter seen to.
A couple of miles driven, and the pump has spent every one of them labouring on diluted fuel. How hard the vehicle was driven matters as much as how far, and the work takes in the tank, your lines, the fuel filter and fresh fuel through the entire system. Short trips, such as the school run to St Dubricius Church of England VA School, are one matter. Getting as far as Cardiff, under 50 miles away, makes a very different task — as does any miles on the M4, under 25 miles from Porlock, with your engine labouring hard all the way.
Rattling, a lumpy idle, smoke, a throttle gone soft: driven until it complained. The fuel is not acting like diesel any more, and the engine is telling you. Stop wherever you are — the verge on Parson's Street, a lay-by, a side street — then leave it there. What goes first is still the fuel drain and flush, and that deals with it, with permanent damage very uncommon if a car is stopped soon.
Porlock motorists and that petrol in a diesel myths they hear
False: topping up to full with diesel makes it fine. It doesn't. A fuller tank of the same mixture is all you get, because topping up removes nothing. That advice presumes 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. At higher pressure, through finer components: that is how a current diesel handles its fuel, so the lubrication counts for more, not less.
"It starts, it drives, and so no harm done" — the myth that catches more people than any other. Feed diesel to a petrol engine and it usually won't run, so the driver stops — and the damage stops with them. Feed petrol to a diesel and it usually starts, idles and drives away like nothing has happened — all the while its pump wears. Being able to run isn't the same as being fine.
An outdated fix for a different problem is behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol weakened is put back by it — and later, that tank still contains the petrol.
If the motor has run, part of that petrol is in your filter and your lines, not that tank — and your next start pulls it right back through your pump. So the myth "drain the tank yourself and you're sorted" does not hold. And, a can of petrol drained at the kerbside is genuinely hazardous.
How it happens: petrol in a diesel
On purpose? Never. Through carelessness? Rarely, if ever. One way only, because of the nozzles: the narrower petrol one slips inside a diesel filler with almost no resistance, while the diesel one generally will not fit a petrol car. That is how the forecourt makes it simple.
Habit and the car falling out of step is how it occurs. Any car that is new to you — hired, on loan as a courtesy car, or just bought. Households running one of each, petrol and diesel. A forecourt you know, but with its pumps laid out differently. A rushed fill on the way to the nearest station with a train to catch. Years of petrol vehicles behind you, a diesel Renault Megane in front of you on the forecourt for its first tank — that is when. Throw in rain, a phone call or a back seat full of kids, and your hand does what it has always done.
Next time you fill up in Porlock: avoiding petrol in a diesel
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most generally do. Read the pump's label; the colour is only a clue.
- The first fill in an unfamiliar motor is the time to check the filler flap — inside it, or on the cap, plenty of 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 household has one of each. So label it.
- "Diesel", aloud, before you pick up the nozzle — each time a new or hired car needs its first tank. It sounds daft. It works.
- While you are 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 designed to refuse a petrol nozzle, and add-on devices exist for cars without one. They are a safety net, not a reason to stop checking the pump.
- Stop the moment you notice. Less petrol inside that tank makes a thinner mix. It doesn't change what to do next, which is still not to start the vehicle.
Petrol already in a diesel around Porlock? Begin here
The order of things is brief, then. Don't crank it, and do not switch the ignition on. If you are still on the forecourt — the nearest petrol station or anywhere else — ask the attendants to help you push the car clear of the pump. Then call 0333 366 0103 and tell us what went in, about how much, and whether it's run.
If it was AdBlue instead of petrol, say so. That's a separate problem — corrosion and deposits rather than lost lubrication — and it has its own page for Porlock.
Why one petrol in a diesel job in Porlock costs more than another
There's no honest single quote for this, since the four scenarios above are four separate tasks. The scenario itself does most of the work of moving the cost. The ratio counts next, meaning how much of that tank is petrol, and then the location of the car and whether reaching it is safe for a technician.
Three queries come first, before any quote, instead of after — what went in, how much, has it run — and this is the reason. Given those answers, there is a straight figure rather than a range.
About Porlock, for a moment
Porlock is a coastal village in Somerset, situated on the south west coast of England, with an elevation of 38 metres above sea level. Porlock lies near the villages of Doverhay, Hawkcombe, and West Luccombe, and is approximately 26 miles from Cardiff. Porlock has a population of around 882 residents, predominantly living in detached housing. Porlock is located about 151 miles west of London, in a scenic area of the South West region.
Porlock and Somerset: where our fuel drain cover reaches
Porlock sits in the TA postcode area, and the vans that answer petrol in diesel jobs there work the spots near it as well — Doverhay, Hawkcombe and West Luccombe among them. The vehicle doesn't need to come to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
In Porlock and still at the petrol pump?
Then you're in the best place there is. Switched off it remains; then ring.