Kents Hill: Petrol in a Diesel Car? How Worried to Be
Likely less than you already are — provided no one has started it. "Have I ruined it?" is the first question anyone in Kents Hill asks, and the honest answer is normally no, because petrol left in a diesel tank harms nothing until it's drawn through the system — by ignition priming, by the starter, or by being driven. Petrol in Diesel is who to phone, with your motor left off, and so it remains that way. The remainder of this page sets out what petrol actually 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 engine: what petrol in a diesel does
On its way through a motor, diesel has two tasks. It lubricates first, and only then does it burn. Made to extremely fine gaps, your injectors and the pump rely on your diesel moving through them to stop their surfaces wearing against one another.
The second task petrol does not do at all, and the first it does poorly. A pump working on a petrol mixture is wearing itself out, because petrol is runnier than diesel and takes away the lubrication the fuel system relies on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that is where any clattering comes.
Together, those make the shape of the problem clear. Not contact but movement is what does the damage. All a tank with petrol in it amounts to is a fuel issue. The start of a mechanical problem is a pump that has been working on that petrol — and whatever a worn pump sheds moves on with your fuel to the injectors downstream.
How bad is petrol in a diesel? Four scenarios our technicians see around Kents Hill
Fuelled but never started — the best it gets. At a forecourt, and really only there, the petrol is still limited to that tank — since anywhere else your car was driven to reach it. The task is draining and purging on the spot.
Started for a moment, or only your ignition on. With your system primed, your lines and filter now hold petrol that came from that tank. Still usually simple: drain, flush, and the fuel filter dealt with.
Those few miles on the road were your pump working on fuel thinned by petrol the whole way. Mileage is only half of it; how hard it was driven matters just as much. Either way the work includes that tank, your lines, your filter and clean fuel through the entire circuit. On the school run to Heronshill School and Nursery, the mileage is small. Getting as far as Milton Keynes, under 3 miles away, makes a very different job — as does any miles on the M1, under 3 miles from Kents Hill, with the motor running hard all the way.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone lumpy. That's your motor telling you its fuel has stopped acting like diesel. Pull up wherever you are — the verge on H9 Groveway, a lay-by, a side street — then leave the car where it is. The fuel drain and flush-through still go first, and they sort it out: if a car is stopped quickly, permanent damage is very rare.
Stories Kents Hill people hear about petrol in a diesel
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. A bigger tank of the same mixture is all it gives, since topping up takes out nothing. A diesel fuel system doesn't accept petrol by percentage in the way that advice supposes.
"Current diesels can handle a little petrol" — a myth, and nearer the reverse. A current diesel sends its fuel through smaller components at higher pressure, which makes the protection matter more, not less.
This is the one that fools motorists. Myth: "If it starts and drives, there is no harm done." Feed diesel to a petrol engine and it normally will not run, and so the driver stops — and the damage stops with them. A diesel fed petrol normally starts, idles and drives away as if nothing has happened, while your pump wears. A running engine doesn't mean fine.
An old fix for a distinct fault lies behind this one. Myth: "Add some two-stroke oil and drive it home." What petrol has weakened stays diluted, and that petrol stays inside the tank anyway.
"Drain it yourself and you're sorted" — a myth, since after it has been running some petrol lies in the filter and lines, waiting to go right back through your pump on your next start. On top of that, petrol emptied into a can by the road is truly hazardous.
Why petrol in a diesel occurs at all
No one does it on purpose, and it's seldom carelessness. The forecourt makes it simple: the petrol nozzle is the narrower of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle mostly won't go into a petrol vehicle at all. So the mistake runs one way.
When routine and the car stop matching, it takes place. Hire cars, courtesy cars, and cars that are new to you. A household with one petrol and one diesel on the drive. A familiar forecourt with the pumps in a different order. Fuelling up in a rush en route to Bow Brickhill, with a train to catch. Exactly the moment it takes place: after years of driving petrol, a driver fills a diesel Volkswagen Golf for the first time. The hand does what it has always done when you add rain, a phone call or a back seat full of kids.
Kents Hill people: how to avoid petrol in a diesel next time
- Check the pump, not the colour. In the UK unleaded handles are generally green and diesel black, yet not on every forecourt. The label is what matters.
- Plenty of motors state the fuel inside your filler flap or on the cap, so check it on the first fill in any car you do not know.
- Good intentions do less than a sticker or a fob in a bright colour on your diesel's key when a house has one of each. So label it.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the pump. It sounds silly and it does the trick.
- While you're thinking about something else, this is an easy mistake to make — so tuck the phone away.
- Add-on devices exist for cars without one, and some diesels are built with a filler that won't accept a petrol nozzle. Helpful — but a backstop only, never a reason to stop checking the label.
- As soon as you notice, stop: less petrol inside your tank means a thinner mix. What to do next does not change, though — still do not crank it.
Already put petrol in a diesel around Kents Hill?
Then the order of things is brief. Starting it is out, and so is switching on the ignition. The staff at the forecourt — whether at Tesco itself or wherever you filled up — will usually help push it clear of the petrol pump if you ask. What went in, about how much, and if it has run: tell us those when you phone 0333 366 0103.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a different issue — Kents Hill has a page all for it.
Why one petrol in a diesel job around Kents Hill costs more than another
Four different tasks sit behind the four situations above — which is why there's no honest single quote. Mostly, your cost shifts with which situation you're in. Two things follow that: the petrol that got in as a proportion of what that tank holds, then the spot the vehicle is in and whether a technician can get to it safely.
Before any quote, not after, we ask three questions: the fuel that was put in, the amount, and whether it has run. That's why. Their answers are what turn a range into one firm number.
About Kents Hill and its setting
Kents Hill is a suburban area in Buckinghamshire, situated near the city of Milton Keynes and approximately 43 miles from London. Kents Hill sits at an elevation of around 74 metres, with semi-detached housing being the predominant type of accommodation in the area. Kents Hill is located close to nearby places such as Walnut Tree, Walton Manor, and Walton Hall, and has a population of around 4727 residents.
Fuel drain cover across Buckinghamshire, Kents Hill included
The teams answering petrol in diesel calls in Kents Hill, in the MK postcode area, equally work the places around it, Walnut Tree, Walton Manor and Walton Hall among them. The vehicle doesn't need to move to us: our technicians drain on a forecourt, in a supermarket car park, in a lay-by or on your own drive.
In Kents Hill and still at the petrol pump?
Then, you could not be in a better spot. Phone, and keep it turned off.