Colney Hatch: Petrol in a Diesel Car? How Worried to Be
Far less than you likely are, if it hasn't been started. Everyone in Colney Hatch begins with "have I wrecked it?", and the fair answer is generally no: petrol resting in that tank of any diesel remains harmless till priming, cranking or driving pulls it into the system. Petrol in Diesel is who to call, with the motor left off, so it remains that way. Below, this page sets out what petrol really does inside a diesel, how far it may have gone, and how to stop it happening to you again.
Petrol in a diesel: what does it do to your engine?
Two jobs fall to diesel on its route round a motor. Lubricating comes before burning; it does both. What stops the surfaces inside the high-pressure fuel pump and the fuel injectors from wearing down against one another is the diesel flowing through them — they are made to very fine tolerances.
Of those two jobs, petrol manages the first poorly and the second not at all. It's runnier than diesel and takes away the lubrication the fuel system depends on, so a pump running on a petrol blend is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That is where the knocking comes from.
The shape of the problem is clear when you put those together. It is movement that does the harm, not contact. A tank with petrol in it is a fuel issue. Whatever a worn pump sheds goes on, borne by the fuel, into the fuel injectors downstream, which is why a pump that has worked on that petrol is where a mechanical fault begins.
Four scenarios our technicians see around Colney Hatch: how serious is petrol in a diesel?
Fuelled, and never started: no case is better. On a forecourt, and genuinely only there, that petrol is still limited to the tank — because anywhere else the vehicle was driven to get to it. The job is emptying and cleaning on the spot.
A moment's running, or merely your ignition on. Once primed, the system has pulled petrol out of your tank up to your filter and the fuel lines. That's usually still a straightforward job — a drain, a flush, and your filter seen to.
Your pump now worked a few miles on diluted fuel — that's what driving the vehicle meant. Tank, lines, filter, then fresh fuel put through the entire circuit: that's this work, and the way the car was driven matters as much as the mileage. Driving the children to Summerside Primary Academy is one kind of trip. Driving as far as London, under 10 miles away, makes a very different job — as does any mileage on the M1, under 3 miles from Colney Hatch, with your engine running hard the whole time.
It complained, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone uneven. What you are hearing is your motor signalling fuel that no longer acts like diesel. Pull up wherever you are — the verge on Pond Close, a lay-by, a side street — and leave it where it is. Long-term damage is very uncommon if a vehicle is stopped quickly, and the drain and flush that still go first deal with it.
Colney Hatch people and that petrol in a diesel stories they hear
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." A fuller tank of the same mix is all you get, because topping up removes nothing. The idea behind the guidance — that diesel fuel systems accept petrol by percentage — is wrong.
If anything, the opposite is true. Myth: "A modern diesel can cope with a bit of petrol." A newer diesel sends its fuel through finer parts at higher pressure, which makes the protection matter more, not less.
This is the one that fools people. Myth: "If it starts and drives, there's no damage done." A petrol motor fed diesel usually will not run, and so the motorist stops and the damage stops with them. Whilst the pump wears, a diesel fed petrol normally starts, ticks over and drives away as if nothing has happened. Being able to run isn't the same as being fine.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an outdated fix for a separate issue. What petrol has weakened remains thinned, and the petrol stays inside that tank regardless.
Myth: "Drain the tank yourself and you are sorted." Once the engine has been run, some of that petrol is no longer in that tank: it is in the fuel filter and the fuel lines, and it goes straight back through your pump at your next start. Clearing petrol into a can at the kerbside is also really risky.
How it happens: petrol in a diesel
No one does it on purpose, and it is seldom carelessness. A diesel nozzle generally will not fit a petrol motor, but the slimmer petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one mistake straightforward, and only in that direction.
When habit and the vehicle stop matching, it occurs. Hire cars, courtesy cars, and cars that are new to you. Households running one of each, petrol and diesel. A forecourt you know, only with its pumps arranged differently. A train to catch, and a rushed fill on the way to New Southgate. The first fill-up in a diesel Renault Clio after years of driving petrol is precisely the moment it takes place. Add rain, a phone call or a back seat full of kids, and your hand repeats what it has always done.
Next time you fill up in Colney Hatch: preventing petrol in a diesel
- A green handle for unleaded and black for diesel is normal in the UK — yet not on each forecourt. Go by the label on the petrol pump, not the colour.
- The first fill in a strange vehicle is the time to check the filler flap — inside it, or on the cap, many cars state the fuel they take.
- One of each in the house? Mark the key to the diesel — a coloured fob, a sticker — because meaning to remember is not enough.
- "Diesel", aloud, before you lift the nozzle — every time a new or hired car gets its first tank. It seems silly. It works.
- Mistakes like this are easy to make while your mind is on something else, so your phone goes away.
- Add-on devices are available for motors without one, and some diesels come with a filler that won't accept a petrol nozzle. Helpful — but a backstop only, never a reason to stop checking the label.
- Less petrol means a weaker mix, so stop the moment you notice — though remembering that your next step is unchanged. It's still not to start the car.
Petrol already in a diesel around Colney Hatch? Start here
Short and simple, then, is the order of things. Don't fire it up, and don't switch your ignition on. Ask the staff to help you roll it clear of the petrol pump if you're still at the forecourt, whether that is the nearest petrol station or somewhere else. Then call 0333 366 0103 and tell us what got in, about how much, and whether it's run.
If it was AdBlue instead of petrol, say so. That's a separate issue — corrosion and deposits and not lost lubrication — and it has its own page for Colney Hatch.
Why one petrol in a diesel job around Colney Hatch costs more than another
Four separate jobs sit behind the four scenarios above — which is why there's no fair single price. The scenario itself does most of the work of moving your cost. Where the vehicle is counts too, and whether our van can safely get to it, after the share of petrol to what your tank takes.
That is why our technicians ask three questions before pricing rather than after: what went in, how much, and whether it has run. Their replies are what turn a range into one firm number.
About Colney Hatch
Colney Hatch is a locality in the London Borough of Barnet, situated near the banks of the Dollis Brook and the Northern Heights. Colney Hatch has a mix of semi-detached housing and other residential properties, with nearby amenities in Friern Barnet and North Finchley. Colney Hatch is located about 7 miles north of central London, at an elevation of around 75 metres above sea level. Colney Hatch remains a suburban area with a population of approximately 2553 residents.
Fuel drain cover across Greater London, Colney Hatch included
Friern Barnet, North Finchley and Coldfall are among the spots near Colney Hatch that the same teams work, answering petrol in diesel jobs across Colney Hatch's N postcode area. A forecourt, a supermarket car park, a lay-by or your own drive are all spots our engineers work, and the car doesn't need to move to us.
In Colney Hatch and still at the petrol pump?
Nothing beats it: that is where you are. Leave it switched off, and ring.