Cobham: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less anxious than you likely feel. "Have I ruined it?" is the first question anyone around Cobham asks, and the truthful answer is usually no, because petrol resting in a diesel tank harms nothing till it's drawn through the fuel system — by ignition priming, by your starter, or by being driven. Leave the engine off and ring Petrol in Diesel — that keeps it that way. What petrol really does to a diesel, how to judge how far it has gone, and how to keep it from happening a second time: that is the remainder of this page.
Inside the motor: what petrol in a diesel does
Diesel has two jobs on its way through an engine. It lubricates to begin with, and after that does it burn. Very fine tolerances go into your injectors and the high-pressure pump, and only the diesel flowing through keeps those surfaces from grinding together.
Badly at the first, not at all at the second: that is petrol. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump on the blend to wear itself. It is equally made to resist igniting under compression — the opposite of what a diesel needs — which is why you get the knocking.
Combined, those make the shape of the trouble plain. Not contact but movement is what does the harm. All a tank with petrol in it amounts to is a fuel issue. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the injectors further on.
How bad is petrol in a diesel? Four situations our engineers see in Cobham
Fuelled up, not once started. The best case there can be. Just your tank has petrol in it, and so the job is draining your tank and rinsing your system where the vehicle stands. This situation can only really occur at a forecourt: anywhere else, the car got there by being driven.
Ignition on, or started for a second. Petrol has left that tank and got to the filter and the fuel lines, since the system has been primed. Usually little more than clearing, flushing and seeing to your filter, and so still easy.
A few miles driven, and your pump has spent every one of them labouring on diluted fuel. The work is the tank, your lines, the filter and clean fuel through the entire circuit, and how hard the vehicle was driven counts as much as how far. A school run to St Andrew's Church of England Primary School is one matter. Getting as far as Westminster, under 25 miles away, makes a very different job — as does any mileage on the M25, under 3 miles from Cobham, with your engine running hard the whole time.
Driven on till it protested — rattling, smoke, a lumpy idle, a soft throttle. The fuel is not behaving like diesel any more, and your motor is telling you. Stop where you are — on the verge on Hollyhedge Road, at the kerb, down a side road — and don't move it again. What goes first is still the fuel drain and flush, and that sorts it out, with lasting damage very unusual when a car is stopped soon.
Stories Cobham drivers hear about petrol in a diesel
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. Nothing is removed by topping up — you are left with a fuller tank, still the same mix. Percentage is not how a diesel fuel system copes with petrol, however much that guidance presumes.
"Current diesels can handle a little petrol" — a myth, and nearer the opposite. A modern diesel runs its fuel through more precise components at higher pressure, which makes the protection matter more, not less.
One myth that catches people off guard: if it starts and drives, it must be unharmed. Diesel in a petrol motor generally means a motor that will not run: the motorist stops, and so does the damage. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile the pump grinds. Running isn't the same as fine.
Myth: a two-stroke additive lets you to drive home. It was an old workaround, meant for another problem. What petrol has diluted remains diluted, and that petrol remains in that tank regardless.
"Drain it yourself and you are sorted" — a myth, because after it's been running some petrol lies in the fuel filter and lines, ready to go straight back through your pump at the next start. It's also genuinely dangerous to drain petrol into a can at the roadside.
Petrol in a diesel: how does it occur?
It is rarely carelessness, and no one does it on purpose. One way only, because of the nozzles: the smaller petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one mostly won't fit a petrol vehicle. That's how the forecourt makes it simple.
The moment routine stops matching the car is the moment it occurs. A new vehicle, a hire car or a courtesy car. A household with one petrol and one diesel on the driveway. A familiar forecourt with the pumps in a different order. A rushed fill on the way to Cobham & Stoke Dabernon with a train to catch. The first fill-up in a diesel Renault Megane after years of driving petrol is precisely the moment it happens. Add a back seat full of kids, a phone call or rain, and habit takes over.
Cobham motorists: how to avoid petrol in a diesel next time
- The label is what matters, so check the petrol pump instead of the colour: in the UK unleaded handles are normally green and diesel black, but not on each forecourt.
- The first fill in an unfamiliar motor is the time to check your filler flap — on it, or on the cap, plenty of vehicles state the fuel they take.
- A coloured fob or a sticker on your diesel's key does more than any amount of intending to remember, in a house with one of each.
- It seems daft and it works: on your first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the pump.
- Tuck the phone away. This is an easy mistake to make while you're thinking about something else.
- Add-on devices exist for motors without one, and some diesels are built with a filler that won't accept a petrol nozzle. Useful — but a backstop only, never a reason to stop checking the label.
- Spotting it mid-fill? Stop at once. A weaker mix results from less petrol in that tank, yet your next step stays the same: do not start it.
Put petrol in a diesel in Cobham already?
In that case, there is just a short order of things. Leave it unstarted, with your ignition switched off too. The attendants at the forecourt — whether at Sainsbury's itself or wherever you filled up — will normally help roll it clear of the petrol pump if you ask. Next, 0333 366 0103. We'll ask what got in, roughly how much, and if it has been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a different fault — Cobham has a page all for it.
One petrol in a diesel job in Cobham costs more than another. Why?
The four scenarios above are four separate tasks, so no single price for this would be fair. Mostly, your cost moves with which situation you are in. Next it's the ratio — how much petrol went in against how much your tank takes — and after that where the vehicle is and whether our van can reach it safely.
Three questions come first, before quoting, instead of after — what got in, how much, has it run — and this is the reason. Those answers turn a range into a straight figure.
About Cobham itself
Cobham is a locality in Surrey, situated on the riverside at an elevation of 24 metres, with semi-detached housing being the predominant type of accommodation. Cobham lies approximately 17 miles from London and is close to nearby places such as Fairmile, Stoke D'Abernon, and Downside. Cobham has a population of around 1794 residents and is located near the city of Westminster. Cobham is characterized by its riverside setting and relatively low elevation.
Fuel drain cover across Surrey, Cobham included
Fairmile, Stoke DAbernon and Downside are among the spots around Cobham that the same teams work, answering petrol in diesel jobs across Cobham's KT postcode area. You need not bring the vehicle to us. Forecourts, supermarket car parks, lay-bys and your own drive are all places where we work.
Still at the petrol pump around Cobham?
The best position there is, then — that's where you are. Keep it off. Call.