Should You Worry? Petrol in a Diesel Car in Nomansland
Less than you probably are, if it has not been started. Till the ignition primes the pump, the starter turns, or the vehicle is driven, petrol in a diesel tank simply waits there and does nothing. Which makes the truthful reply to the first Nomansland question — "have I ruined it?" — usually no. Leave the engine off and call Petrol in Diesel — that is how you keep it like that. The remainder of this page sets out what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
What petrol in a diesel does to the engine
Passing through an engine, diesel is doing two jobs at once. Lubricating comes before burning; it does both. Very fine tolerances are built into the injectors and the high-pressure pump, and just your diesel running through keeps those surfaces from grinding together.
Badly at the first, not at all at the second: that's petrol. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump running on that mixture wearing itself. It is equally made to resist igniting under compression — the reverse of what a diesel needs — which is why you hear the knocking.
The shape of the issue is clear once you put those together. Not contact but circulation is what causes the harm. Petrol in a tank is a fuel issue. A pump that has been labouring on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with the fuel to your injectors further on.
Four situations our engineers see around Nomansland: how serious is petrol in a diesel?
Fuelled up, not once started. The best case there can be. On a forecourt, and really only there, that petrol is still confined to that tank — since everywhere else the vehicle was driven to get to it. The job is emptying and flushing on the spot.
Your ignition turned on, or a brief start. Once primed, the fuel system has pulled petrol out of your tank as far as the fuel filter and the lines. Drain, flush, deal with the fuel filter: still usually straightforward.
A few miles driven, and your pump has spent each of them labouring on thinned fuel. Miles is only half of it; how hard it was driven counts equally. Either way the work runs to the tank, the lines, the fuel filter and clean fuel through the entire system. Short trips, such as the school run to The New Forest Church of England Primary School, are one thing. Getting as far as Salisbury, under 15 miles away, makes a very different job — as does any miles on the M27, under 5 miles from Nomansland, with the motor labouring hard the whole time.
Driven on till it protested — clattering, smoke, a ragged idle, a dead throttle. That's the engine telling you its fuel has stopped acting like diesel. Pull up wherever you are — the verge on School Road, a lay-by, a side street — and leave it where it is. What comes first is still the fuel drain and flush-through, and that sorts it out, with long-term damage very rare if a car is pulled over early.
What Nomansland drivers get told about petrol in a diesel — and the stories in it
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing is removed by topping up — you're left with a bigger tank, still the same mixture. Percentage is not how a diesel fuel system tolerates petrol, however much that advice supposes.
"Modern diesels can handle a little petrol" — a myth, and closer to the reverse. More precise parts and higher pressure are how a newer diesel runs its fuel, and that makes the lubrication matter more, not less.
"It starts, it drives, and so there is no harm" — the myth that trips up more people than any other. 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. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile your pump wears. Being able to run isn't proof of being fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a distinct fault. It does not put back what petrol has weakened, and the petrol is still inside that tank later.
"Drain it yourself and you're sorted" — a myth, because after it has been running some petrol lies in the filter and lines, waiting to go straight back through the pump at the next start. Also, a can of petrol filled at the roadside is truly dangerous.
How petrol ends up: petrol in a diesel
On purpose? Never. Through carelessness? Rarely, if ever. The forecourt makes it simple: the petrol nozzle is the narrower of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle generally won't go into a petrol motor at all. So the error runs one way.
It occurs when habit and the vehicle stop matching. Courtesy car, hire car, or a car that is brand new. 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 en route to Dean. A new-to-you diesel Volkswagen Passat, its first fuelling, and a motorist accustomed to petrol: exactly when it takes place. The hand repeats what it has always done when you add rain, a phone call or a back seat full of kids.
Next time you fill up in Nomansland: avoiding petrol in a diesel
- Read the pump, not the colour. In the UK unleaded handles are normally green and diesel black, but not on each forecourt. The label is what matters.
- Many cars state the fuel type inside your filler flap or on the cap, and so check it on your first fill in any vehicle you don't know.
- Good intentions count for less than a sticker or a fob in a bright colour on the diesel's key when a household has one of each. So mark it.
- Before the nozzle leaves the pump the first time you fuel a hired or new car, say "diesel" aloud. Silly, yes, but it works.
- Thinking about something else is when this becomes an easy mistake to make, so put the phone away and keep your mind on the pump.
- Some diesels have a filler designed to block a petrol nozzle, and devices you can add are available for cars without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the petrol pump.
- Stop as soon as you notice. Less petrol in that tank means a weaker mixture. It doesn't change what to do next, which is still not to start the car.
Petrol already in a diesel around Nomansland? Begin here
The order of things is brief, then. Don't switch the ignition on, and don't start it. The staff on the forecourt — whether at BP itself or wherever you filled up — will normally help push it away from the petrol pump if you ask. What went in, about how much, and whether it has run: tell us that when you phone 0333 366 0103.
Corrosion and deposits form the trouble with AdBlue, where petrol means lost lubrication. So if it was AdBlue, say so — and see its own Nomansland page.
What makes one Nomansland petrol in a diesel job cost more than the next
An honest single quote doesn't exist here: four situations, four separate jobs. The scenario itself does most of the work of moving the cost. After that it's the share — how much petrol went in against how much the tank holds — and after that where your car is and whether a van 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. A range turns into a straight figure when those replies are in.
About Nomansland, briefly
Nomansland is a small village in Wiltshire, situated inland at an elevation of 73 metres, approximately 10 miles from Salisbury. Nomansland has a population of around 649 people, predominantly living in detached houses. Nomansland is surrounded by nearby villages such as Landford, Hamptworth, and Bramshaw, and is about 75 miles west of London.
Fuel drain cover across Wiltshire, Nomansland included
Landford, Hamptworth and Bramshaw are among the locations around Nomansland that the same vans work, answering petrol in diesel call-outs across Nomansland's SP postcode area. The car does not need to move to us: our engineers drain at a forecourt, in a supermarket car park, in a lay-by or on your own drive.
In Nomansland and still at the pump?
The best position there is, then — that's where you are. Call, and keep it turned off.