Sunken Marsh: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less anxious than you probably are. Till your ignition primes your pump, the starter cranks, or your vehicle is driven, petrol in a diesel tank simply sits there and does no harm. Which makes the honest reply to the first Sunken Marsh query — "have I ruined it?" — usually no. Leave the engine off and ring Petrol in Diesel — that keeps it that way. The rest of this page explains what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it does not happen to you a second time.
What petrol in a diesel does to the motor
Passing through a motor, diesel does two things at the same time. 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 each other is your diesel passing through them — they're designed to very fine tolerances.
Petrol handles the first job badly and the second not at all. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump on the mixture wearing itself. It is also made to resist igniting under compression — the opposite of what a diesel needs — which is why you get the knocking.
Put those together and the shape of the problem is plain. Contact does not do the harm — circulation does. A tank with petrol in it is a fuel fault. After the pump has been running on that petrol, a mechanical issue has begun: whatever is shed by a pump that is wearing travels onward to your injectors with the fuel.
How bad is petrol in a diesel? Four situations our engineers see in Sunken Marsh
Filled up, and not started: nothing beats it. Being at a forecourt is what makes this the case: elsewhere, the vehicle has been driven there to begin with. With that petrol kept inside your tank alone, it is drained and rinsed on the spot, and nothing more is needed.
Ignition on, or started for a second. Once primed, your system has drawn petrol out of your tank up to the filter and your lines. Still usually easy: drain, flush, and your filter dealt with.
Driven a few miles. Now your pump has spent those miles working on thinned fuel. The work is your tank, the fuel lines, your filter and clean fuel through the entire system, and how hard the vehicle was driven matters as much as how far. Driving the children to St Joseph's Catholic Primary School and Nursery is one kind of trip. Very different a second time: a trip to Southend-on-Sea, under 5 miles away, or any mileage on the M2, under 15 miles from Sunken Marsh, where the motor never stopped working hard.
Driven on till it complained — clattering, smoke, a ragged idle, a dead throttle. What you are hearing is your engine signalling fuel that no longer behaves like diesel. Stop wherever you are — the verge on Laars Avenue, a lay-by, a side street — then leave the car where it is. What comes first is still the fuel drain and flush, and that deals with it, with lasting damage very unusual if a car is pulled over soon.
What Sunken Marsh motorists get told about petrol in a diesel — and the stories in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." Nothing is removed when you top up — the tank simply holds more of the same mixture. That guidance supposes a diesel fuel system handles petrol by percentage. It doesn't.
If anything, the reverse is true. Myth: "A newer diesel can cope with a bit of petrol." At higher pressure, through smaller components: that is how a modern diesel moves its fuel, and so the lubrication matters more, not less.
The myth that catches people off guard: if it starts and drives, it must be unharmed. The driver of a petrol engine fed diesel usually has no choice but to stop, since it will not run, and the harm stops there. While your pump wears, a diesel fed petrol normally starts, idles and drives away as though nothing has happened. Being able to run is not proof of being fine.
An old workaround for a different issue lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol diluted gets put back by it — and afterwards, your tank still contains that petrol.
Myth: "Drain your tank yourself and you are sorted." Once your engine has run, some of the petrol is no longer in the tank: it is in the filter and the fuel lines, and it goes right back through the pump at your next start. It is also really risky to drain petrol into a can by the kerbside.
How petrol ends up: petrol in a diesel
On purpose? Never. Through carelessness? Rarely, if ever. The petrol nozzle is the smaller of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol motor at all. The forecourt makes it simple, and the slip runs one way.
It takes place when habit and your car stop matching. A new car, a hire car or a courtesy car. Two motors on one drive, one petrol, one diesel. A familiar forecourt with the pumps in a different order. A train to catch, and a rushed fill on the way to Benfleet. Years of petrol cars behind you, a diesel Volkswagen Golf in front of you at the forecourt for its first tank — that's when. The hand does what it has always done when you add rain, a phone call or a back seat full of kids.
Next time you fill up around Sunken Marsh: preventing petrol in a diesel
- Green 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 — on it, or on the cap, many vehicles state which fuel they take.
- Good intentions do less than a sticker or a fob in a vivid colour on your diesel's key when a household has one of each. So mark it.
- "Diesel", out loud, before you pick up the nozzle — each time a new or hired car needs its first tank. It sounds daft. It does the trick.
- Thinking about something else is when this becomes an easy mistake to make, so tuck the phone away and keep your mind on the pump.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler designed to reject a petrol nozzle, and add-on devices are available for cars without one. They are a safety net, not a reason to stop reading the petrol pump.
- Stop as soon as you notice. Less petrol inside the tank means a weaker mix. It doesn't change what to do next, which is still not to start the vehicle.
Sunken Marsh: already put petrol in a diesel?
The order of things is brief, then. Don't turn the ignition on, and don't fire it up. The staff on the forecourt — whether at Sainsbury's itself or wherever you filled up — will usually help roll it clear of the pump if you ask. Then call 0333 366 0103 and tell us what was put in, about how much, and if it's run.
Say so if it was AdBlue rather than petrol: it's a different problem, with its own page for Sunken Marsh, because AdBlue brings corrosion and deposits rather than lost protection.
One petrol in a diesel task around Sunken Marsh costs more than another. Why?
Four different jobs sit behind the four situations above — which is why there's no honest single quote. Which of them you're in is chiefly what shifts the cost. Two things come after that: the petrol that went in as a proportion of what that tank takes, then the place the vehicle is in and whether a technician can reach it safely.
Three queries come first, before quoting, rather than after — what went in, how much, has it run — and that is the reason. Those answers turn a range into a straight figure.
About Sunken Marsh, for a moment
Sunken Marsh is a coastal suburban area in Essex, situated near the mouth of the Thames estuary and close to the seaside town of Southend-on-Sea. Sunken Marsh lies at a low elevation of around 4 metres, making it a relatively flat and low-lying area. Sunken Marsh is characterised by its predominantly detached housing stock and its proximity to nearby places such as Canvey Island and Leigh Beck.
Fuel drain cover around Sunken Marsh and across Essex
Our vans answering petrol in diesel call-outs in Sunken Marsh, in the SS postcode area, also work the places around it, Canvey Island, Newlands and Leigh Beck included. A forecourt, a supermarket car park, a lay-by or your own drive are all places we drain, and your vehicle doesn't need to move to us.
In Sunken Marsh and still at the petrol pump?
Then, you could not be in a better spot. Ring, and keep it switched off.