Birnam: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less worried than you likely are. "Have I ruined it?" is the first thing anyone in Birnam asks, and the truthful answer is normally no, because petrol left in a diesel tank harms nothing till it's drawn through your fuel system — by ignition priming, by your starter, or by driving. Petrol in Diesel is who to call, with the motor kept off, so it remains that way. What petrol actually does to a diesel, how to gauge how far it's travelled, and how to keep it from happening a second time: that is the rest of this page.
Petrol in a diesel: what does it do to your engine?
Passing through a motor, diesel is doing two things at the same time. It burns, and before it combusts it lubricates. The high-pressure pump and your injectors are built to extremely fine clearances, and the diesel passing through them is what stops those surfaces from wearing against each other.
The second job petrol doesn't do at all, and the first it does badly. Being less viscous than diesel, petrol strips away the protection a fuel system needs, so a pump on the mixture to wear itself. It is equally made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the knocking.
Put those together and the shape of the problem is clear. The damage is done by circulation, not by contact. Where that petrol is only in the tank, it is a problem of fuel, nothing more. A pump that has been running on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the fuel injectors downstream.
Birnam, petrol in a diesel: four cases, from mild to significant
The best case there can be: filled up, not once started. That petrol is inside that tank and only your tank, and the job is a drain and a flush where the car stands. This is the one scenario that can only really happen at a forecourt, since anywhere else the vehicle has been driven to get there.
Ignition on, or started for a second. Petrol has left your tank and reached the fuel filter and your lines, because the fuel system has been bled. That's usually still a simple task — a drain, a flush, and your filter dealt with.
A couple of miles driven, and the pump has spent each of them labouring on thinned fuel. The work is your tank, the lines, the filter and clean fuel through the entire circuit, and how hard your car was driven counts as much as how far. On the school run to the local primary school, the miles is short. Driving as far as Perth, under 15 miles away, makes a very different task — as does any distance on the M90, under 15 miles from Birnam, with the engine labouring hard all the way.
Driven till it protested. Knocking, a ragged idle, smoke, a throttle that has gone soft. That is your motor telling you its fuel has stopped acting like diesel. Whether it is the verge on Gladstone Terrace, a lay-by or a side street, stop there and leave it. A car pulled over early very rarely has permanent damage, because the drain and the flush-through, which still go first, take care of it.
Petrol in a diesel myths Birnam people hear
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Topping up removes nothing; it gives you a fuller tank of the same mixture. Percentage isn't how a diesel fuel system tolerates petrol, whatever that guidance supposes.
Myth: a modern diesel copes with a bit of petrol. Rather, the opposite. Protection counts more on newer diesels, not less, because their fuel runs through more precise components at higher pressure.
One myth that catches motorists off guard: if it starts and drives, it must be unharmed. Feed diesel to a petrol motor and it generally won't run, and so the motorist stops — and the harm 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. Being able to run isn't proof of being fine.
Myth: a two-stroke additive lets you to drive home. It was an old workaround, supposed for another fault. None of what petrol diluted is put back by it — and afterwards, that tank still holds the petrol.
"Drain it yourself and you are sorted" — a myth, because after it has been running some petrol sits in the fuel filter and lines, waiting to go right back through your pump on the next start. It is also really dangerous to drain petrol into a can by the roadside.
How petrol ends up: petrol in a diesel
It's seldom carelessness, and nobody does it on purpose. One way only, since of the nozzles: the narrower petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one mostly won't fit a petrol motor. That is how the forecourt makes it easy.
When habit and the vehicle stop matching, it takes place. A new motor, a hire car or a courtesy car. Two cars on one drive, one petrol, one diesel. A forecourt you know, but with its pumps laid out differently. Rushing for a train outside Dunkeld & Birnam and fuelling up en route. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist accustomed to petrol: exactly when it takes place. With rain, a call arriving, or children to deal with, your hand simply does what it has always done.
How to avoid petrol in a diesel at your next fill-up in Birnam
- Green for unleaded and black for diesel is normal in the UK — yet not on each forecourt. Trust the label on the petrol pump, not the colour.
- The first fill in a new car is the time to check the filler flap — on it, or on the cap, plenty of cars state which fuel to use.
- A coloured fob or a sticker on the diesel's key does more than any amount of intending to remember, in a household with one of each.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the pump. It seems daft and it works.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck the phone away.
- Add-on devices exist for cars without one, and some diesels come with a filler that won't accept a petrol nozzle. Useful — but a safety net at best, never a reason to stop checking the label.
- Less petrol makes a thinner mix, and so stop as soon as you realise — while remembering that the next stage is unchanged. It's still not to fire it up.
Birnam: already put petrol in a diesel?
Short and simple, then, is the order of things. Starting it is out, and so is turning on your ignition. Ask the attendants to help you push it clear of the pump if you are still on the forecourt, whether that is Pace or anywhere else. Next, 0333 366 0103. We'll ask what was put in, about how much, and if it's been run.
If it was AdBlue and not petrol, say so. That is a separate issue — corrosion and deposits instead of lost lubrication — and it has its own page for Birnam.
Why one petrol in a diesel task around Birnam costs more than another
An honest single quote doesn't exist here: four scenarios, four separate jobs. What moves your cost is chiefly which of them you're in. Two things follow 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 reach it safely.
Three queries come first, before any quote, instead of after — what went in, how much, has it run — and that is the reason. Given the answers, you get a straight figure rather than a range.
About Birnam, briefly
Birnam is a small village situated on the banks of the River Tay in Perth and Kinross, with a population of around 545 people. Birnam sits at an elevation of 64 metres, close to the nearby villages of Little Dunkeld and Dunkeld. Birnam is characterized by its predominantly detached housing stock, reflecting its rural setting. Birnam is located near the city of Perth, approximately 12 miles away.
Birnam and Perth and Kinross: where our fuel drain cover runs
Petrol in diesel calls in Birnam — part of the PH postcode area — go to teams that also cover the places round it, Little Dunkeld, Dunkeld and Inver among them. No need to bring your vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all locations where we work.
In Birnam and still at the pump?
In that case, you could not be in a better position. Ring, and leave it switched off.