How Worried Should You Be? Petrol in a Diesel Car in Knaphill
Not started? Then less anxious than you likely feel. "Have I wrecked it?" is the first thing anyone around Knaphill asks, and the honest answer is generally no, since petrol left in a diesel tank harms nothing till it's dragged through the fuel system — by ignition priming, by the starter, or by driving. Keep it that way: leave the motor off then call Petrol in Diesel. The rest of this page explains what petrol really does to a diesel, how to tell how far it has got, and how to make sure it doesn't happen to you again.
The engine and petrol in a diesel: what happens
Two jobs fall to diesel on its journey round a motor. Before it ignites, it protects — then it combusts. Very fine tolerances go into the injectors and the high-pressure fuel pump, and only your diesel flowing through stops their surfaces grinding together.
Badly at the first, not at all at the second: that is petrol. A pump running on a petrol mix is wearing itself out, since petrol is thinner than diesel and takes away the lubrication your fuel system depends on. Petrol is also made to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that's where any clattering starts.
Combined, those leave the shape of the issue plain. It's movement that causes the damage, not contact. Any tank with petrol in it is a fuel fault. The start of a mechanical one is a pump that has been running on that petrol — and whatever a worn pump sheds travels on with your fuel to your injectors downstream.
Knaphill, petrol in a diesel: four situations, from mild to serious
Fuelled, and not started: nothing beats it. Being on a forecourt is what makes this the case: elsewhere, your car has been driven there to begin with. With the petrol held inside your tank alone, it is drained and flushed on the spot, and nothing more is needed.
Your ignition switched on, or a short start. Petrol has left your tank and reached your filter and the fuel lines, since the system has been primed. That is usually still a straightforward task — a drain, a flush, and your filter seen to.
Driven a couple of miles. Now your pump has spent those miles running on diluted fuel. Tank, lines, filter, then fresh fuel run through the whole circuit: that's this work, and the way the vehicle was driven counts as much as the mileage. Short trips, like the school run to St John's Primary School, are one thing. Very different a second time: a run to Westminster, under 25 miles away, or any mileage on the M3, under 5 miles from Knaphill, where the engine kept running hard.
Rattling, a lumpy idle, smoke, a throttle gone soft: driven until it complained. What you are hearing is your engine reporting fuel that no longer behaves like diesel. Leave it where it stops: a lay-by, a quiet street, the verge on Wood Lane. Long-term damage is very rare when a car is stopped quickly, and the drain and flush-through that still go first take care of it.
Knaphill motorists and that petrol in a diesel myths they hear
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Nothing is removed by topping up — you are left with a fuller tank, still the same mixture. The idea behind that guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Newer diesels can handle a little petrol" — a myth, and closer to the opposite. At higher pressure, through smaller components: that is how a current diesel moves its fuel, and so the protection matters more, not less.
Myth: "If it starts and drives, there's no harm done." This is the one that catches people. Diesel in a petrol motor normally means a motor that will not run: the driver stops, and so does the damage. While the pump grinds, a diesel fed petrol usually starts, idles and drives away as if nothing has happened. Fine and running aren't the same at all.
An outdated fix for a separate problem lies behind this one. Myth: "Add some two-stroke oil and drive it home." It does not put back what petrol has thinned, and that petrol is still in the tank later on.
If the engine has been run, part of that petrol sits in your filter and the lines, not your tank — and your next start sends it right back through the pump. So the myth "drain the tank yourself and you're sorted" doesn't hold. It is also really dangerous to drain petrol into a can by the kerbside.
Petrol in a diesel: how does it happen?
It is rarely carelessness, and no one does it on purpose. The forecourt makes it easy: the petrol nozzle is the slimmer of the two, and it slides into a diesel filler with almost no resistance, while a diesel nozzle generally will not go into a petrol car at all. So the slip runs one way.
The moment routine stops matching the car is the moment it takes place. Hire cars, courtesy cars, and vehicles that are new to you. One petrol and one diesel on the drive of the same household. A well-known forecourt with the pumps in a different order. A train to catch, and a rushed fill en route to Brookwood. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is exactly the moment it takes place. Your hand does what it has always done once you add rain, a phone call or a back seat full of kids.
Knaphill motorists: how to prevent petrol in a diesel next time
- A green handle for unleaded and black for diesel is normal in the UK — yet not on every forecourt. Trust the label on the petrol pump, not the colour.
- Inspect your filler flap. Plenty of motors state the fuel type inside the flap or on the cap. Look at it on your first fill in any motor you do not know.
- Good intentions do less than a sticker or a fob in a bright colour on the diesel's key if a house has one of each. So label it.
- Before the nozzle comes off the pump the first time you fuel a hired or new vehicle, say "diesel" out loud. Silly, yes, but it works.
- Thinking about something else is when this becomes an easy mistake to make, so tuck your phone away and keep your mind on the petrol pump.
- 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 motors without one. They are a backstop, not a reason to stop checking the petrol pump.
- As soon as you realise, stop: less petrol inside the tank means a thinner mixture. What to do next doesn't change, though — still do not crank it.
Knaphill: already put petrol in a diesel?
Then the order of things is brief. Don't turn your ignition on, and don't fire it up. Yet at the forecourt, at Esso or anywhere else? Ask the staff to help you push the car away from the petrol pump. Next, 0333 366 0103. We'll ask what got in, roughly how much, and if it's been run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost lubrication, make it a different fault — Knaphill has a page just for it.
Why one petrol in a diesel job around Knaphill costs more than another
An honest single price doesn't exist here: four situations, four separate tasks. What shifts your cost is chiefly which of them you are in. Where your car is matters too, and whether a van can safely get to it, after the share of petrol to what that tank takes.
Three queries come first, before any quote, instead of after — what was put in, how much, has it run — and this is the reason. Given those replies, there is a straight figure instead of a range.
About Knaphill, for a moment
Knaphill is a suburban area in Surrey, situated approximately 24.7 miles southwest of London. Knaphill sits at an elevation of 54 metres, surrounded by other localities such as Whitfield Court, Littlewick, and Bisley. Knaphill has a population of around 7953 residents, predominantly living in semi-detached housing. Knaphill is characterized by its inland setting, with the nearest city being Westminster, located about 24.6 miles away.
Across Surrey and in Knaphill: fuel drain cover
The teams answering petrol in diesel jobs around Knaphill, in the GU postcode area, also work the places around it, Whitfield Court, Littlewick and Bisley included. You need not move the car to us. Forecourts, supermarket car parks, lay-bys and your own drive are all spots where we work.
Still at the petrol pump around Knaphill?
Then, you couldn't be in a better place. Keep the vehicle turned off, and ring.