How Worried Should You Be? Petrol in a Diesel Car in Law
If it hasn't been started, worry far less than you probably are. Everyone in Law starts with "have I wrecked it?", and the fair answer is generally no: petrol left in your tank of any diesel stays harmless till priming, cranking or driving pulls it into the system. Leave the motor off and call Petrol in Diesel — that is how you keep it like that. Keep reading for three things: the effect petrol has inside a diesel engine, the signs of how far it has got, and the way to make sure you never do it again.
Inside your engine: what petrol in a diesel really does
Diesel does two tasks on its way through a motor. It ignites, and before it combusts it protects. Very fine gaps are built into the injectors and the high-pressure pump, and just the diesel running through keeps their surfaces from grinding together.
Of these two jobs, petrol manages the first badly and the second not at all. A pump running on a petrol blend is wearing itself out, because petrol is runnier than diesel and takes away the protection the fuel system relies on. Petrol is also designed to resist igniting under compression — the reverse of what a diesel wants from its fuel — and that's where the rattling starts.
Taken together, they show what shape the problem takes. The harm is done by movement, not by contact. Where the petrol is only in that tank, it is a fault of fuel, nothing more. The start of a mechanical problem is a pump that has been labouring on that petrol — and whatever a worn pump sheds moves on with the fuel to the fuel injectors downstream.
Law, petrol in a diesel: four situations, from mild to significant
Fuelled up, not once started. The best case there is. That petrol is in that tank and only the tank, and the job is a drain and a flush where the vehicle sits. This is the one situation that can only truly take place on a forecourt, as anywhere else your car has been driven to get there.
Started for a second, or only the ignition on. Once primed, your system has pulled petrol out of your tank as far as the filter and the lines. Drain, flush, deal with the filter: still normally straightforward.
A few miles driven, and the pump has spent every one of them labouring on weakened fuel. Distance is only half of it; how hard it was driven matters equally. Either way this work includes that tank, the lines, the filter and clean fuel through the whole circuit. On the school run to the local primary school, the miles is small. Any distance on the M74, under 3 miles from Law, means your engine has worked hard throughout, and a run to Glasgow, under 25 miles away, is a very different job as well.
Knocking, a ragged idle, smoke, a throttle gone soft: driven until it complained. The motor is telling you the fuel is no longer behaving like diesel. Stop on the spot — on the verge on Shawfield Crescent, 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 vehicle is stopped soon, long-term damage is very rare.
Law motorists 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 when you top up — your tank just carries more of the same mixture. A diesel fuel system does not accept petrol by percentage in the way that advice supposes.
"Modern diesels can handle a little petrol" — a myth, and nearer the reverse. At higher pressure, through smaller components: that's how a current diesel handles its fuel, so the lubrication matters for more, not less.
"It starts, it drives, so there is no harm" — the myth that trips up more motorists than any other. Any petrol engine fed diesel usually will not run, and so the motorist stops and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually will; meanwhile the pump wears. Running isn't the same as fine.
An outdated fix for a distinct fault is behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." That petrol is still inside that tank after that, and whatever it has thinned is not put back.
"Drain it yourself and you're sorted" — a myth, since after it has been running some petrol lies in the filter and lines, ready to go right back through your pump on the next start. On top of that, petrol cleared into a can by the road is genuinely hazardous.
How does petrol in a diesel occur?
Nobody does it on purpose, and it's seldom carelessness. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle mostly will not go into a petrol car at all. So the error runs one way.
Habit and the vehicle getting out of step is how it happens. Courtesy car, hire car, or a vehicle that's new. Two cars on one drive, one petrol, one diesel. Your usual forecourt, its pumps now in a different order. Fuelling up in a hurry on the way to Carluke, with a train to catch. Years of petrol motors behind you, a diesel Volkswagen Passat in front of you on the forecourt for its first tank — that's when. Throw in rain, a phone call or a back seat full of children, and your hand does what it has always done.
How to prevent petrol in a diesel at your next fill-up around Law
- Green for unleaded and black for diesel is usual in the UK — but not on every forecourt. Trust the label on the petrol pump, not the colour.
- The first fill in a strange car is the time to check your filler flap — inside it, or on the cap, many vehicles state the fuel to use.
- A coloured fob or a sticker on your diesel's key does more than any amount of intending to remember, in a house with one of each.
- It sounds daft and it works: on your first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the pump.
- Mistakes like this are simple to make whilst your mind is on something else, so your phone goes away.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to block a petrol nozzle, and add-on devices exist for vehicles without one. They are a backstop, not a reason to stop checking the petrol pump.
- Stop the moment you realise. Less petrol in that tank means a thinner blend. It doesn't change what to do next, which is still not to crank it.
Already put petrol in a diesel around Law?
Then the order of things is brief. Don't turn the ignition on, and don't crank it. The staff on the forecourt — whether at BP itself or wherever you filled up — will usually help push it away from the petrol pump if you ask. Next, 0333 366 0103. We will ask what was put in, about how much, and if it has been run.
Corrosion and deposits are the issue with AdBlue, whereas petrol brings lost protection. So if it was AdBlue, say so — and read its own Law page.
One petrol in a diesel task around Law costs more than another. Why?
An honest single quote doesn't exist here: four scenarios, four separate jobs. The situation itself does most of the work of moving your cost. Two things come after that: the petrol that was put in as a share of what that tank holds, then the place the car is in and whether a technician can get to it safely.
Ahead of any quote, not after, come three questions: the fuel that got in, the amount, and if it has run. That's why. With those replies, you get a straight figure instead of a range.
About Law, for a moment
Law is a village in South Lanarkshire, situated inland at an elevation of 169 metres, approximately 15.8 miles southeast of Glasgow. Law sits near the settlements of Wildmanbridge and Overtown, and is close to the notable Law Hill. Law has a population of around 2027 people, predominantly living in semi-detached housing.
Fuel drain cover in Law and across South Lanarkshire
Law waits in the ML postcode area, and our vans that answer petrol in diesel jobs there work the locations near it as well — Wildmanbridge, Law Hill and Overtown among them. Our technicians drain wherever your car is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
In Law and still at the pump?
Then you're in the best position there can be. Keep it off. Call.