How Worried Should You Be? Petrol in a Diesel Car in The Knapp
Not started? Then less worried than you likely feel. "Have I ruined it?" is the first thing anyone around The Knapp asks, and the honest answer is normally no, because petrol resting in a diesel tank hurts nothing until it is dragged through the system — by ignition priming, by the starter, or by driving. Petrol in Diesel is who to ring, with your engine left off, so it stays that way. Further down, you will find what petrol actually does inside a diesel, how far it might have gone, and how to stop it happening to you again.
Inside your engine: what petrol in a diesel does
Two tasks fall to diesel on its route round a motor. It burns, and before it burns it lubricates. What keeps the surfaces inside the high-pressure fuel pump and the fuel injectors from wearing down against one another is the diesel passing through them — they are made to extremely fine tolerances.
Petrol handles the first task badly and the second not at all. A pump working on a petrol blend is wearing itself out, since petrol is thinner than diesel and takes away the protection your 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's where the rattling starts.
Combined, those make the shape of the trouble plain. Not contact but circulation is what does the damage. All a tank with petrol in it amounts to is a fuel fault. After your pump has been running on that petrol, a mechanical problem has begun: anything shed by a pump that's wearing down travels onward to your injectors with the fuel.
The Knapp, petrol in a diesel: four cases, from mild to serious
Fuelled, and never started: nothing beats it. Being at a forecourt is what makes this the case: elsewhere, the car has been driven there to begin with. With the petrol kept in the tank alone, it is drained and rinsed on the spot, and nothing more is needed.
Started for a moment, or only your ignition on. Once primed, the system has pulled petrol out of the tank as far as your filter and your lines. Drain, flush, see to the fuel filter: still usually straightforward.
Those few miles driven were the pump working on fuel weakened by petrol the whole way. The work is the tank, your lines, the filter and clean fuel through the entire system, and how hard your car was driven counts as much as how far. Driving the children to St Peter's Primary School is one sort of trip. Any mileage on the M5, under 15 miles from The Knapp, means your engine working hard throughout, and a run to Worcester, under 15 miles away, makes a very different task as well.
Driven on until it complained — rattling, smoke, a lumpy idle, a soft throttle. That is the motor telling you its fuel has stopped acting like diesel. Pull up wherever you are — the verge on York Road, a lay-by, a side street — and leave the car there. The fuel drain and flush still go first, and they take care of it: if a car is stopped soon, long-term damage is very rare.
The Knapp motorists and that petrol in a diesel stories they hear
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing is removed when you top up — your tank simply carries more of the same blend. Percentage is not how a diesel fuel system tolerates petrol, whatever that guidance assumes.
"Newer diesels can handle a little petrol" — a myth, and nearer the opposite. Lubrication counts more on current diesels, not less, because their fuel runs through smaller components at higher pressure.
Myth: "If it starts and drives, there is no harm done." This is the one that fools drivers. Feed diesel to a petrol motor and it generally won't run, so the motorist stops — and the damage stops with them. Feed petrol to a diesel and it usually fires up, idles and pulls away like nothing has happened — all the while its pump is wearing. Running isn't the same as fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a different issue. None of what petrol weakened is put back by it — and later, your tank still holds the petrol.
Once the engine has been run, part of that petrol is in the filter and your lines, not the tank — and the next start pulls it straight back through the pump. So the myth "drain that tank yourself and you are sorted" doesn't stand up. It's also really hazardous to drain petrol into a can by the kerbside.
How does petrol in a diesel take place?
A careless moment is rarely the cause, and nobody means to do it. The petrol nozzle is the slimmer of the two and slips into a diesel filler with almost no resistance; a diesel nozzle generally will not go into a petrol car at all. The forecourt makes it easy, and the slip runs one way.
The moment habit stops matching your car is the moment it takes place. Hire cars, courtesy cars, and cars that are new to you. Households running one of each, petrol and diesel. A forecourt you know, but with its pumps arranged differently. Filling up in a hurry en route to Malvern Link, with a train to catch. Years of petrol cars behind you, a diesel Renault Megane in front of you at the forecourt for its first tank — that is when. With rain, a call arriving, or children to deal with, the hand just does what it always has.
Next time you fill up in The Knapp: preventing petrol in a diesel
- Green for unleaded and black for diesel is usual in the UK — but 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 your filler or at the cap before your first fill: many vehicles print the fuel type there.
- Mark your key. In a house with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the petrol pump. It seems silly and it does the trick.
- Put the phone away. This is an easy mistake to make whilst you're thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to refuse a petrol nozzle, and aftermarket devices are available for the remainder. Treat it as a safety net, and keep reading the petrol pump.
- Stop as soon as you realise. Less petrol in the tank means a thinner mix. It doesn't change what to do next, which is still not to start the vehicle.
The Knapp: already put petrol in a diesel?
Then, there is only a short order of things. Do not start the car, and don't turn your ignition on. Ask the attendants to help you push it away from the pump if you are still on the forecourt, whether that's Texaco or somewhere else. Then call 0333 366 0103 and tell us what got in, roughly how much, and if it's run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost lubrication, make it a different problem — The Knapp has a page just for it.
One petrol in a diesel task in The Knapp costs more than another. Why?
Four separate tasks lie behind the four scenarios above — which is why there is no honest single quote. Chiefly, the cost moves with which one you are in. After that it's the ratio — how much petrol was put in against how much that tank takes — and then where the car is and whether our van can get to it safely.
Before any quote, not after, come three questions: the fuel that was put in, the amount, and if it's run. That is why. Those replies turn a range into a straight figure.
About The Knapp and its setting
The Knapp is a suburban area situated on the riverside in Herefordshire, with a mix of semi-detached housing and other residential properties. The Knapp sits at an elevation of 149 metres, close to the nearby settlements of West Hill and Flaggoners Green. The Knapp is located near the city of Worcester, which is approximately 12 miles away, and is part of the wider West Midlands region. The Knapp has a population of around 3816 people, living in a variety of housing types, predominantly semi-detached homes.
Fuel drain cover around The Knapp and across Herefordshire
Our teams answering petrol in diesel calls around The Knapp, in the HR postcode area, equally work the spots near it, West Hill, Flaggoners Green and Bromyard included. A forecourt, a supermarket car park, a lay-by or your own drive are all locations our engineers drain, and the car doesn't need to come to us.
Still at the pump around The Knapp?
The best place there is, then — that's where you are. Keep the car switched off, and ring.