--- title: Marsh Mills: Petrol in a Diesel Car, Explained canonical: https://www.petrolinadieselcar.co.uk/petrol-in-diesel/marsh-mills-devon/ location: Marsh Mills county: Devon latitude: 50.391710 longitude: -4.084030 service: Petrol in a Diesel Car updated: 2026-10-12 --- # Petrol in a Diesel Car in Marsh Mills: How Worried Should You Be? Not started? Then less anxious than you probably feel. Until your ignition primes the pump, your starter turns, or the vehicle is driven, petrol in a diesel tank just waits there and does nothing. Which makes the honest reply to that first Marsh Mills query — "have I wrecked it?" — usually no. Leave the engine off and call Petrol in Diesel — that is how you keep it like that. What petrol really does to a diesel, how to gauge how far it's gone, and how to keep it from happening again: that is the remainder of this page. ## The engine and petrol in a diesel: what goes on On its way through a motor, diesel has two tasks. It lubricates to begin with, and only then does it burn. What keeps 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 extremely fine gaps. Petrol handles the first task badly and the second not at all. Being less viscous than diesel, petrol strips out the protection a fuel system needs, leaving a pump on that mixture wearing itself. It's also made to resist igniting under compression — the opposite of what a diesel needs — which is where you get the rattling. The shape of the trouble is clear when you put those together. Contact does not do the harm — circulation does. Any tank with petrol in it is a fuel problem. Once your pump has been running on that petrol, a mechanical issue has begun: whatever is shed by a pump that's grinding travels onward to your injectors with your fuel. ## Four situations our engineers see around Marsh Mills: how serious is petrol in a diesel? Filled up, never started. The best case there can be. Being at a forecourt is what makes this the case: elsewhere, your car has been driven there to begin with. With the petrol kept inside that tank alone, it is drained and flushed on the spot, and nothing more is needed. Started for a second, or just the ignition on. Once primed, the fuel system has drawn petrol out of your tank as far as the filter and the lines. Still normally simple: drain, flush, and the fuel filter dealt with. A few miles driven, and your pump has spent every one of them working on diluted fuel. How hard your car was driven counts as much as how far, and this work covers that tank, the lines, the fuel filter and clean fuel through the entire circuit. On the school run to Woodford Primary School, the mileage is short. Any mileage on the M5, under 50 miles from Marsh Mills, means the engine has worked hard throughout, and a run to Plymouth, under 5 miles away, is a very different job too. Driven until it protested. Clattering, a ragged idle, smoke, a throttle that has gone soft. The engine is telling you your fuel is no longer acting like diesel. Pull up wherever you are — the verge on Plymouth Road, a lay-by, a side street — and leave the vehicle there. A vehicle stopped quickly very rarely has permanent damage, because the drain and the flush, which still come first, take care of it. ## Marsh Mills people and the petrol in a diesel myths they hear "Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. Nothing is removed by topping up — you are left with a bigger tank, still the same mixture. Percentage isn't how a diesel fuel system tolerates petrol, whatever that guidance supposes. "Current diesels can handle a little petrol" — a myth, and nearer the opposite. A newer diesel sends its fuel through smaller components at higher pressure, which makes the lubrication matter more, not less. This is the one that catches people. Myth: "If it starts and drives, there's no harm done." A petrol motor fed diesel normally won't run, and so the driver stops and the damage stops with them. Whilst the pump wears, a diesel fed petrol usually starts, idles and drives away as though nothing has happened. Running does not mean fine. An old fix for a separate issue lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." The petrol is still inside the tank afterwards, and whatever it has diluted isn't put back. If the motor has run, part of the petrol is in the filter and the fuel lines, not your tank — and your next start sends it right back through the pump. So the myth "drain the tank yourself and you are sorted" doesn't hold. It is also truly risky to drain petrol into a can at the kerbside. ## Why petrol in a diesel takes place at all Carelessness is rarely the cause, and nobody means to do it. The petrol nozzle is the smaller of the two and slips into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol motor at all. The forecourt makes it easy, and the slip runs one way. Habit and the car getting out of step is how it takes place. Hire cars, courtesy cars, and cars that are new to you. Households running one of each, petrol and diesel. The pumps in a different order on a familiar forecourt. A train to catch, and a hurried fill on the way to Plymouth. A new-to-you diesel Volkswagen Passat, its first fuelling, and a driver used to petrol: exactly when it occurs. Throw in rain, a phone call or a back seat full of kids, and the hand does what it has always done. ## Next time you fill up in Marsh Mills: avoiding petrol in a diesel - Green for unleaded and black for diesel is usual in the UK — yet not on each forecourt. Go by the label on the petrol pump, not the colour. - In a vehicle you don't know, look inside the flap over the filler or at the cap before your first fill: many motors print the fuel type there. - Good intentions count for less than a sticker or a fob in a vivid colour on the diesel's key if a household has one of each. So label it. - It seems daft and it does the trick: on your first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the petrol pump. - Whilst you're thinking about something else, this is an easy mistake to make — so tuck the phone away. - A misfuel inhibitor helps, up to a point. Some diesels come with a filler designed to reject a petrol nozzle, and add-on devices exist for cars without one. They are a safety net, not a reason to stop reading the petrol pump. - As soon as you realise, stop: less petrol inside that tank makes a weaker blend. What to do next doesn't change, though — still do not crank it. ## Put petrol in a diesel in Marsh Mills already? Then the order of things is brief. Leave it unstarted, with your ignition switched off as well. The attendants on the forecourt — whether at Sainsbury's itself or wherever you filled up — will usually help roll it clear of the petrol pump if you ask. Then phone 0333 366 0103 and tell us what went in, roughly how much, and if it's run. Say so if it was AdBlue rather than petrol: it's a different issue, with its own page for Marsh Mills, because AdBlue brings corrosion and deposits instead of lost lubrication. ## One petrol in a diesel task around Marsh Mills costs more than another. Why? The four situations above are four separate tasks, so no single quote for this would be fair. Chiefly, your cost moves with which situation you're in. Two things follow that: the petrol that went in as a proportion of what the tank holds, then the spot the car is in and whether our van can get to it safely. Ahead of any quote, not after, come three queries: your fuel that was put in, its quantity, and if it has run. That's why. Those answers are what turn a range into one firm number. ## About Marsh Mills, briefly Marsh Mills is a suburban area located on the coast of Devon, near the city of Plymouth. Marsh Mills sits at a low elevation of around 4 metres, close to the shores of the Plym Estuary. Marsh Mills is characterized by its predominantly semi-detached housing stock, with nearby neighbourhoods including Longbridge and Crabtree. Marsh Mills is situated approximately 3 miles from Plymouth city centre, making it a convenient residential location. ## Across Devon and around Marsh Mills: fuel drain cover Longbridge, Crabtree and Woodford are among the places near Marsh Mills that the same vans work, answering petrol in diesel call-outs across Marsh Mills's PL postcode area. The car 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 driveway. ## At the petrol pump around Marsh Mills, right now? Nothing beats it: that's where you now are. Ring, and leave it turned off.