--- title: Worried? Petrol in a Diesel Car Felthamhill canonical: https://www.petrolinadieselcar.co.uk/petrol-in-diesel/felthamhill-surrey/ location: Felthamhill county: Surrey latitude: 51.428310 longitude: -0.422980 service: Petrol in a Diesel Car updated: 2026-10-01 --- # Felthamhill: Petrol in a Diesel Car? How Worried to Be If it hasn't been started, worry less than you likely are. Petrol sitting in a diesel tank does nothing to the engine till something draws it through the fuel system — your ignition priming your pump, the starter, or driving itself. So the truthful answer to the first question anyone around Felthamhill asks, "have I wrecked it?", is generally no. Leave your engine off then phone Petrol in Diesel — that keeps it like that. Keep reading for three things: the effect petrol has inside a diesel motor, the clues of how far it has got, and the way to make sure you don't do it again. ## What petrol in a diesel does to the engine Diesel does two jobs on its way through a motor. It protects to begin with, and after that does it burn. Extremely fine tolerances go into your injectors and your high-pressure pump, and just the diesel running through stops those surfaces grinding together. Of those two jobs, petrol manages the first badly and the second not at all. A pump working on a petrol mix is wearing itself out, since petrol is runnier than diesel and strips out the protection your fuel system relies on. Petrol is also made to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that is where any clattering comes. Together, those leave the shape of the trouble clear. It's circulation that causes the harm, not contact. All a tank with petrol in it amounts to is a fuel fault. The beginning of a mechanical problem is a pump that has been labouring on that petrol — and whatever a worn pump sheds travels on with the fuel to your injectors beyond it. ## Four scenarios we see in Felthamhill: how bad is petrol in a diesel? Fuelled, and never started: nothing beats it. The petrol is inside your tank and just the tank, and the task is a drain and a flush where your car stands. This is the one scenario that can only really happen at a forecourt, because anywhere else your car has been driven to get there. The ignition turned on, or a short start. Petrol has come out of the tank and reached your filter and your lines, because the system has been bled. Drain, flush, see to the filter: still normally simple. Those few miles on the road were your pump labouring on fuel diluted by petrol the whole way. Distance is only half of that; how hard it was driven matters equally. Either way this work includes your tank, your lines, the fuel filter and fresh fuel through the whole circuit. Short trips, such as the school run to Kenyngton Manor Primary School, are one matter. Any mileage on the M3, under a mile from Felthamhill, means the motor has worked hard throughout, and a run to Westminster, under 15 miles away, makes a very different task as well. Driven until it complained. Clattering, a ragged idle, smoke, a throttle that has gone soft. What you are hearing is your engine reporting fuel that no longer acts like diesel. Pull up on the spot — on the verge on King's Avenue, at the kerb, down a side road — and don't move it again. The drain and flush still go first, and they take care of it: if a car is stopped early, long-term damage is very rare. ## Felthamhill drivers and the petrol in a diesel stories they hear "Top it up the rest of the way with diesel and it will be fine" — a myth. It will not. Topping up takes out nothing; it gives you a bigger tank of the same mixture. That advice supposes a diesel fuel system tolerates petrol by percentage. It doesn't. If anything, the opposite is true. Myth: "A current diesel can cope with a bit of petrol." A current diesel sends its fuel through finer parts at higher pressure, which makes the lubrication matter more, not less. This is the one that fools people. Myth: "If it starts and drives, there's no harm done." A petrol motor fed diesel usually won't run, and so the driver stops and the harm stops with them. While the pump wears, a diesel fed petrol usually starts, ticks over and drives away as if nothing has happened. Being able to run is not proof of being fine. An outdated fix for a different problem lies behind this one. Myth: "Add some two-stroke oil and drive the car home." None of what petrol diluted gets put back by it — and later, the tank still contains that petrol. The next start draws petrol back round your pump out of the fuel lines and your filter, where some of it ends up once the engine has run. That's why a DIY tank drain does not sort it — a myth. On top of that, petrol cleared into a can by the road is truly risky. ## Why petrol in a diesel happens at all A careless moment is rarely the cause, and no one means to do it. A diesel nozzle mostly will not fit a petrol vehicle, yet the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one error simple, and just in that direction. It occurs when routine and the vehicle stop matching. Hire cars, courtesy cars, and vehicles that are new to you. One petrol and one diesel on the driveway of the same household. Your normal forecourt, its pumps now in a different order. A train to catch, and a hurried fill en route to Kempton Park. Years of petrol vehicles behind you, a diesel Renault Megane in front of you on the forecourt for its first tank — that's when. With rain, a call arriving, or a car full of children to deal with, the hand just does what it has always done. ## Next time you fill up in Felthamhill: preventing petrol in a diesel - The label is what matters, and so check the pump instead of the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt. - The first fill in a strange car is the time to check the filler flap — on it, or on the cap, plenty of motors state the fuel they take. - A coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember, in a home with one of each. - 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 seems daft and it works. - While you're thinking about something else, this is an easy mistake to make — so put your phone away. - A misfuel inhibitor helps, up to a point. Some diesels have a filler designed to block a petrol nozzle, and add-on devices are available for motors without one. They are a backstop, not a reason to stop checking the petrol pump. - As soon as you notice, stop: less petrol in your tank means a weaker blend. What to do next does not change, though — still do not start the car. ## Petrol already in a diesel in Felthamhill? Begin here The order of things is short, then. Don't crank it, and don't switch your ignition on. Still on the forecourt, at Tesco or anywhere else? Ask the attendants to help you roll the car away from the petrol pump. Then call 0333 366 0103 and tell us what got in, about how much, and if it's run. If it was AdBlue rather than petrol, say so. That is a different fault — corrosion and deposits and not lost lubrication — and it has its own page for Felthamhill. ## Felthamhill petrol in a diesel jobs: why one costs more than another A fair single quote does not exist here: four scenarios, four separate jobs. The situation itself does most of the work of moving the cost. Two things come after that: the petrol that was put in as a proportion of what that tank takes, then the spot the car is in and whether a van can reach it safely. That's why our technicians ask three questions before costing instead of after: what was put in, how much, and if it has run. With the answers, there is a straight figure rather than a range. ## About Felthamhill itself Felthamhill is a suburban area in Surrey, situated on the riverside with an elevation of around 14 metres. Felthamhill lies close to Ashford Common and Sunbury Common, and is characterized by its semi-detached housing stock. Felthamhill is located near Lower Feltham and is part of the wider suburban landscape surrounding London. Felthamhill has a population of approximately 6280 residents. ## Fuel drain cover across Surrey, Felthamhill included Our teams answering petrol in diesel calls around Felthamhill, in the TW postcode area, equally work the locations around it, Ashford Common, Sunbury Common and Lower Feltham among them. The vehicle doesn't need to move to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway. ## Felthamhill: still at the petrol pump? Nothing beats it: that's where you now are. Switched off it remains; then phone.