Coombe: Petrol in a Diesel Car? How Worried to Be
Probably less than you are now — as long as no one has started the car. Everyone around Coombe begins with "have I wrecked it?", and the honest answer is normally no: petrol left inside that tank of any diesel stays harmless till priming, cranking or driving pulls it into your fuel system. Keep it like that: leave your motor off then phone Petrol in Diesel. What petrol actually does to a diesel, how to gauge how far it's gone, and how to stop it from happening again: that's the remainder of this page.
The engine and petrol in a diesel: what goes on
On its way through a motor, diesel does two jobs. Before it burns, it lubricates — and then it ignites. Very fine clearances are built into the injectors and the high-pressure pump, and just the diesel running through stops their surfaces grinding together.
Of those two jobs, petrol manages the first poorly and the second never. The knocking comes from petrol being designed not to ignite when compressed, which is exactly the opposite of what a diesel needs. On top of that it is runnier than diesel, it strips out the protection the fuel system hinges on, and any pump working on such a mixture is wearing itself.
Seen together, they make clear the shape the issue has. The harm is done by circulation, not by contact. Petrol in a tank is a fuel fault. After your pump has been working on that petrol, a mechanical issue has started: anything shed by a pump that is wearing down is carried onward to the injectors with your fuel.
How serious is petrol in a diesel? Four situations our engineers see in Coombe
Filled up, and never started: nothing beats it. On a forecourt, and truly only there, that petrol is still limited to that tank — because everywhere else your car was driven to reach it. The job is emptying and rinsing on the spot.
The ignition turned on, or a short start. Petrol has come out of your tank and reached the fuel filter and the lines, since the fuel system has been primed. Normally nothing more than emptying, cleaning and sorting the fuel filter, so still easy.
The pump now worked a couple of miles on diluted fuel — that's what driving the vehicle does. Miles is only half of that; how hard it was driven counts just as much. Either way this work includes the tank, the fuel lines, the filter and clean fuel through the entire circuit. Short trips, such as the school run to Ash Cartwright and Kelsey Church of England Primary School, are one thing. Driving as far as Canterbury, under 10 miles away, makes a very different task — as does any mileage on the M20, under 15 miles from Coombe, with your engine running hard the whole time.
Driven on until it protested — rattling, smoke, an uneven idle, a dead throttle. What you are hearing is the engine reporting fuel that no longer runs like diesel. Pull up wherever you are — the verge on Coombe Lane, a lay-by, a side street — and leave the car where it is. Long-term damage is very unusual when a car is stopped soon, and the drain and flush-through that still go first sort it out.
Stories Coombe drivers hear about petrol in a diesel
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. A fuller tank of the same mix is all you get, since topping up takes out nothing. That advice supposes a diesel fuel system handles petrol by percentage. It doesn't.
Myth: a modern diesel copes with a bit of petrol. If anything, the reverse. A current diesel runs its fuel through finer components at higher pressure, which makes the lubrication count more, not less.
Myth: "If it starts and drives, there is no harm done." This is the one that catches motorists. Any petrol motor fed diesel normally won't run, so the motorist stops and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile the pump wears. Running does not mean fine.
Myth: "Add some two-stroke oil and drive the car home." It is an outdated fix for a separate fault. It does not put back what petrol has weakened, and the petrol is still inside the tank afterwards.
"Drain it yourself and you're sorted" — a myth, because after it has been running some petrol sits in the fuel filter and lines, waiting to go straight back through your pump at your next start. Also, a can of petrol drained by the roadside is truly dangerous.
How petrol ends up: petrol in a diesel
No one does it on purpose, and it is seldom carelessness. The petrol nozzle is the narrower of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol motor at all. The forecourt makes it easy, and the error runs one way.
It happens when habit and your car stop matching. Courtesy car, hire car, or a motor that's brand new. Households running one of each, petrol and diesel. The pumps in a different order on a well-known forecourt. Filling up in a hurry en route to Sandwich, with a train to catch. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is exactly the moment it takes place. With rain, a call coming in, or children to deal with, your hand simply does what it has always done.
How to avoid petrol in a diesel on your next fill-up around Coombe
- The label is what counts, so read the pump instead of the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt.
- In a motor you do not know, look inside the flap over your filler or at the cap before your first fill: many vehicles state the fuel there.
- Mark your 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 intending to remember.
- It sounds daft and it works: on the first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the petrol pump.
- While you're thinking about something else, this is an easy mistake to make — so put the phone away.
- Add-on devices exist for cars without one, and some diesels are built with a filler that won't take a petrol nozzle. Helpful — but a backstop at best, never a reason to stop checking the label.
- Less petrol makes a weaker mix, so stop as soon as you notice — though remembering that the next stage is unchanged. It is still not to start the car.
Petrol already in a diesel around Coombe? Start here
Then, there's only a short order of things. Never crank it, and don't switch the ignition on. Still on the forecourt, at Gulf or anywhere else? Ask the attendants to help you roll the vehicle clear of the petrol pump. Ring 0333 366 0103 next, with three facts — your fuel, the rough volume, and if it has run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a different problem — Coombe has a page just for it.
What makes one Coombe petrol in a diesel job cost more than the next
Four separate jobs lie behind the four situations above — which is why there's no honest single price. Mostly, your cost shifts with which situation you are in. Two things come after that: the petrol that went in as a proportion of what your tank takes, then the place the car is in and whether a technician can reach it safely.
That's why our technicians ask three queries before quoting rather than after: what was put in, how much, and whether it has run. Those answers turn a range into a straight figure.
About Coombe itself
Coombe is a small hamlet situated on the riverside in Kent, with a low elevation of around 23 metres. Coombe lies near the cities of Canterbury and the surrounding villages of Marshborough, Flemings, and Ash. Coombe is characterized by its predominantly detached housing stock and is located approximately 63 miles from London. Coombe has a small population of around 555 residents.
Across Kent and in Coombe: fuel drain cover
Coombe rests in the CT postcode area, and our teams that answer petrol in diesel jobs there work the places near it as well — Marshborough, Flemings and Ash among them. We drain wherever your vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
In Coombe and still at the pump?
The best spot there is, then — that's where you are. Phone, and leave it switched off.