--- title: Worried? Petrol in a Diesel Car Newtown canonical: https://www.petrolinadieselcar.co.uk/petrol-in-diesel/newtown-cambridgeshire-pe29-1/ location: Newtown county: Cambridgeshire latitude: 52.331810 longitude: -0.173550 service: Petrol in a Diesel Car updated: 2026-10-28 --- # Petrol in a Diesel Car in Newtown: How Worried Should You Be? Provided it has not been started, worry far less than you probably are. Everyone around Newtown starts with "have I wrecked it?", and the honest answer is usually no: petrol resting in the tank of any diesel remains harmless until priming, cranking or driving pulls it into the system. Petrol in Diesel is who to ring, with the motor left off, so it stays that way. Read on for three things: the effect petrol has inside a diesel motor, the clues of how far it has spread, and the way to make sure you never do it again. ## The motor and petrol in a diesel: what happens Two tasks fall to diesel on its route through a motor. Before it burns, it protects — and then it burns. Extremely fine clearances are built into your injectors and the high-pressure fuel pump, and just the diesel running through stops their surfaces grinding together. Badly at the first, not at all at the second: that's petrol. It is thinner than diesel and strips away the lubrication your fuel system depends on, and so a pump running on a petrol mixture is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That is where the knocking comes from. Together, those make the shape of the trouble clear. It is circulation that causes the harm, not contact. Any tank with petrol in it is a fuel issue. After your pump has been working on that petrol, a mechanical fault has started: whatever is shed by a pump that is wearing down is carried onward to the fuel injectors with your fuel. ## Petrol in a diesel around Newtown: how bad is it? Four cases Fuelled but not once started — the best it gets. Only the tank has petrol in it, so the job is draining that tank and purging the system where the car sits. This scenario can only really take place on a forecourt: anywhere else, the vehicle got there by being driven. Started for a moment, or only the ignition on. Petrol has come out of the tank and got to the fuel filter and your lines, since your system has been bled. Normally nothing more than emptying, flushing and sorting the filter, so still straightforward. Driven a couple of miles. Now the pump has spent those miles labouring on weakened fuel. How hard the vehicle was driven counts as much as how far, and the work takes in your tank, the fuel lines, the filter and clean fuel through the whole system. The school run to Hartford Junior School is one matter. A run as far as Cambridge, under 25 miles away, is a very different task. So is any mileage on the A1(M), under 5 miles from Newtown, where the engine has been running hard the whole time. Driven till it protested. Knocking, an uneven idle, smoke, a throttle that has gone soft. The motor is telling you the fuel is no longer acting like diesel. Leave it wherever it stops: a lay-by, a side street, the verge on Hartford Road. A vehicle stopped early very rarely has permanent damage, because the drain and the flush-through, which still come first, sort it out. ## Newtown people and the petrol in a diesel myths they hear Myth: topping up to full with diesel makes it fine. It doesn't. Topping up takes out nothing; it gives you a fuller tank of the same mixture. A diesel fuel system does not tolerate petrol by percentage in the way that guidance supposes. "Current diesels can handle a little petrol" — a myth, and closer to the opposite. Finer parts and higher pressure are how a modern diesel runs its fuel, and that makes the protection count more, not less. Myth: "If it starts and drives, there's no damage done." This is the one that fools motorists. The driver of a petrol motor fed diesel usually stops, because it will not run, and the damage stops with them. Feed petrol to a diesel and it generally starts, ticks over and pulls away like nothing has happened — all the while its pump is wearing. Fine and running are not the same at all. Not so: a two-stroke additive makes it safe to drive home. It is an old fix, supposed for another problem. It does not put back what petrol has weakened, and the petrol is still inside your tank later. Myth: "Drain your tank yourself and you are sorted." Once your engine has run, some of the petrol is no longer inside your tank: it's in the fuel filter and the fuel lines, and it goes right back through your pump at the next start. And, a can of petrol drained by the roadside is genuinely hazardous. ## Petrol in a diesel: how does it take place? Carelessness is rarely the cause, and nobody means to do it. One way only, since of the nozzles: the narrower petrol one slips inside a diesel filler with almost no resistance, whereas the diesel one mostly will not fit a petrol motor. That's how the forecourt makes it easy. The moment habit stops matching the car is the moment it occurs. Any vehicle that is new to you — hired, on loan as a courtesy car, or just bought. One petrol and one diesel on the drive of the same household. Your usual forecourt, its pumps suddenly in a different order. Rushing for a train outside Huntingdon and filling up en route. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is exactly the moment it happens. Throw in 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 around Newtown: preventing petrol in a diesel - Not every forecourt in the UK follows green for unleaded and black for diesel, though most generally do. Check the petrol pump's label; the colour is only a clue. - The first fill in a new car is the time to check your filler flap — on it, or on the cap, many vehicles state which fuel they take. - One of each in the household? Label your key to your diesel — a coloured fob, a sticker — since meaning to remember isn't enough. - Say it before you lift it. On the first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the petrol pump. It sounds silly and it does the trick. - Mistakes like this are straightforward to make whilst your mind is on something else, and so the phone goes away. - A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to refuse a petrol nozzle, and add-on devices exist for vehicles without one. They are a safety net, not a reason to stop reading the pump. - Stop the moment you notice. Less petrol in that tank means a weaker mix. It doesn't change what to do next, which is still not to fire it up. ## Put petrol in a diesel in Newtown already? In that case, there's only a short order of things. Starting it is out, and so is switching on your ignition. Yet on the forecourt, at Sainsbury's or anywhere else? Ask the staff to help you roll the car away from the pump. Ring 0333 366 0103 next, with three answers — your fuel, the approximate amount, and whether it's run. If it was AdBlue and not petrol, say so. That's a separate problem — corrosion and deposits instead of lost lubrication — and it has its own page for Newtown. ## What makes one Newtown petrol in a diesel task cost more than the next Four separate jobs sit behind the four situations above — which is why there's no fair single price. The situation itself does most of the work of moving the cost. Where your car is matters too, and whether our van can safely get to it, after the share of petrol to what that tank takes. That's why we ask three questions before pricing instead of after: what got in, how much, and if it has run. Those answers are what turn a range into one firm number. ## About Newtown Newtown is a suburban area in Cambridgeshire, situated on the riverside with an elevation of around 14 metres. Newtown lies near the city of Cambridge, approximately 15 miles to the northwest, and is also close to other nearby places such as Huntingdon, Hartford, and Godmanchester. Newtown has a population of around 3703 people and predominantly consists of semi-detached housing. ## Fuel drain cover across Cambridgeshire, Newtown included Petrol in diesel jobs around Newtown — part of the PE postcode area — go to teams that also cover the places around it, Huntingdon, Hartford and Godmanchester included. A forecourt, a supermarket car park, a lay-by or your own driveway are all spots our engineers drain, and the vehicle does not need to come to us. ## At the petrol pump in Newtown, right now? No position is better: that's where you now are. Keep the car switched off, then ring.