The Butts: Petrol in a Diesel Car? How Worried to Be
Not started? Then less worried than you likely are. Petrol sitting in a diesel tank does nothing to your motor until something pulls it through the system — the ignition priming your pump, the starter, or the drive on its own. So the truthful answer to the first question everyone in The Butts asks, "have I wrecked it?", is normally no. Leave your engine off and ring Petrol in Diesel — that is how you keep it that way. The remainder of this page sets out 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 a second time.
Inside the motor: what petrol in a diesel really does
Two jobs fall to diesel on its route round a motor. Before it burns, it lubricates — then it ignites. Made to very fine gaps, the fuel injectors and your pump rely on your diesel moving through them to stop their surfaces wearing against one another.
Poorly at the first, not at all at the second: that's petrol. A pump working on a petrol mixture is wearing itself out, since petrol is runnier than diesel and strips out the lubrication your 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 the knocking starts.
Seen together, they make clear the shape the trouble has. It is circulation that does the damage, not contact. Any tank with petrol in it is a fuel issue. The start of a mechanical problem is a pump that has been running on that petrol — and whatever a worn pump sheds moves on with your fuel to your injectors downstream.
Four situations our technicians see around The Butts: how bad is petrol in a diesel?
Filled up, and not started: nothing beats it. The petrol is inside the tank and only that tank, and the task is a drain and a flush where the car stands. This is the one situation that can only really occur at a forecourt, because anywhere else your car has been driven to get there.
Ignition on, or started for a moment. Once primed, your system has pulled petrol out of that tank up to the filter and your lines. Usually nothing more than draining, purging and sorting the fuel filter, and so still simple.
Those few miles driven were the pump running on fuel weakened by petrol the whole way. The work is the tank, the fuel lines, the filter and clean fuel through the entire system, and how hard the car was driven matters as much as how far. A school run to The Butts Primary School is one thing. A run as far as Winchester, under 25 miles away, is a very different task. So is any miles on the M3, under 10 miles from The Butts, where your engine has been running hard throughout.
Driven until it protested. Clattering, a lumpy idle, smoke, a throttle that has gone soft. What you are hearing is the engine reporting fuel that no longer runs like diesel. Pull up where you are — on the verge on Lincoln Green, at the kerb, down a side road — and do not move it. The drain and flush-through still go first, and they take care of it: when a car is pulled over quickly, permanent damage is very rare.
Stories The Butts drivers hear about petrol in a diesel
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. Nothing is removed by topping up — you're left with a fuller tank, still the same mix. The idea behind that advice — that diesel fuel systems accept petrol by percentage — is wrong.
"Newer diesels can handle a little petrol" — a myth, and nearer the opposite. Lubrication counts more on newer diesels, not less, since their fuel passes through more precise components at higher pressure.
Myth: "If it starts and drives, there is no harm done." This is the one that catches motorists. Diesel in a petrol motor usually means a motor that will not run: the driver stops, and so does the harm. While the pump wears, a diesel fed petrol usually starts, ticks over and drives away as though nothing has happened. A running engine doesn't mean fine.
Myth: "Add some two-stroke oil and drive the vehicle home." It is an outdated fix for a separate problem. None of what petrol thinned is put back by it — and later, that tank still contains the petrol.
Myth: "Drain that tank yourself and you're sorted." Once the engine has run, some of the petrol is no longer inside that tank: it's in your filter and the fuel lines, and it goes straight back through your pump at the next start. Emptying petrol into a can at the kerbside is also really hazardous.
Petrol in a diesel: how does it happen?
On purpose? Never. Through carelessness? Rarely, if ever. The petrol nozzle is the smaller of the two and slips into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol car at all. The forecourt makes it easy, and the slip runs one way.
It takes place when habit and the car stop matching. Hire cars, courtesy cars, and motors that are new to you. Two cars on one drive, one petrol, one diesel. The pumps in a different order on a familiar forecourt. A rushed fill en route to Alton with a train to catch. The first fill-up in a diesel Renault Megane after years of driving petrol is exactly the moment it happens. With rain, a call coming in, or a car full of children to deal with, the hand simply does what it always has.
Next time you fill up around The Butts: avoiding petrol in a diesel
- The label is what counts, and so check the petrol pump instead of the colour: in the UK unleaded handles are usually green and diesel black, yet not on each forecourt.
- The first fill in an unfamiliar vehicle is the time to check the filler flap — on it, or on the cap, plenty of motors state which fuel to use.
- One of each in the house? Label the key to the diesel — a bright fob, a sticker — since intending to remember is not enough.
- It sounds daft and it does the trick: on the first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the pump.
- Put the phone away. This is an easy mistake to make while you're thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to block a petrol nozzle, and aftermarket devices exist for the rest. Count it as a safety net, and keep reading the petrol pump.
- Noticing it halfway? Stop there and then. A weaker mix follows from less petrol inside that tank, yet your next stage remains the same: don't start the car.
The Butts: already put petrol in a diesel?
Short and simple, then, is the order of things. Starting it is out, and so is switching on the ignition. If you're still at the forecourt — BP or anywhere else — ask the attendants to help you roll the vehicle away from the petrol pump. Then ring 0333 366 0103 and tell us what was put in, roughly how much, and whether it's run.
Say so if it was AdBlue rather than petrol: it is a separate fault, with its own page for The Butts, because AdBlue brings corrosion and deposits instead of lost lubrication.
The Butts petrol in a diesel tasks: why one costs more than another
The four situations above are four separate tasks, so no single quote for this would be honest. Mostly, your cost moves with which one you're in. The ratio matters next, meaning how much of your tank is petrol, followed by the location of your car and whether getting to it is safe for a van.
Three queries come first, before any quote, rather than after — what got in, how much, has it run — and that is the reason. Their replies are what turn a range into one firm number.
About The Butts
The Butts is a suburban area situated on the riverside in Hampshire, with a mix of detached housing and a population of around 4863 residents. The Butts sits at an elevation of 115 metres, approximately 15 miles from the city of Winchester and 44 miles from London. The Butts is located near other local areas such as Newtown, Mount Pleasant, and Alton, and is part of the wider South East region. The Butts has a relatively quiet setting, with the river running nearby.
Fuel drain cover across Hampshire, The Butts included
The teams answering petrol in diesel jobs in The Butts, in the GU postcode area, equally work the places near it, Newtown, Mount Pleasant and Alton among them. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations we drain, and your vehicle doesn't need to move to us.
In The Butts and still at the petrol pump?
Then you're in the best spot there is. Ring, and keep it turned off.