Muirton: Petrol in a Diesel Car? How Worried to Be
Probably less than you are now — provided nobody has started it. Petrol sitting in a diesel tank does nothing to your engine till something pulls it through the system — your ignition priming your pump, your starter, or driving itself. So the honest answer to the first query everyone in Muirton asks, "have I wrecked it?", is generally no. Petrol in Diesel is who to ring, with the motor left off, and so it stays that way. Keep reading for three things: the effect petrol has inside a diesel engine, the clues of how far it has spread, and ways to make sure you never do it again.
Inside your engine: what petrol in a diesel really does
On its way through an engine, diesel does two jobs. Before it combusts, it protects — then it combusts. The high-pressure fuel pump and your injectors are designed to very fine gaps, and the diesel passing through them is what stops those surfaces from grinding against each other.
Of these two tasks, petrol handles the first poorly and the second not at all. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump on that 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 clattering.
Seen together, they show the shape the trouble takes. It is movement that does the damage, not contact. Where the petrol is only inside your tank, it's an issue of fuel, nothing more. After your pump has been working on that petrol, a mechanical problem has begun: anything shed by a pump that's wearing down travels downstream to the injectors with the fuel.
Muirton, petrol in a diesel: four situations, from mild to significant
Fuelled up, not once started. The best case there can be. On a forecourt, and genuinely only there, the petrol is still limited to your tank — because everywhere else the car was driven to reach it. The job is emptying and purging on the spot.
Started for a second, or only the ignition on. With your system primed, the lines and filter already hold petrol that has come from that tank. Usually nothing more than draining, cleaning and seeing to your filter, so still easy.
Your pump has worked a few miles on weakened fuel — that's what driving the vehicle meant. Tank, lines, filter, then clean fuel put through the entire system: that's the work, and the way the car was driven counts as much as the mileage. Short trips, such as the school run to the local primary school, are one thing. A run as far as Perth, under 3 miles away, is a very different task. So is any distance on the M90, under 3 miles from Muirton, where your engine has been working hard throughout.
Driven until it protested. Clattering, an uneven idle, smoke, a throttle that has gone soft. The engine is telling you your fuel is no longer acting like diesel. Stop wherever you are — the verge on Uist Place, a lay-by, a side street — then leave it there. Long-term damage is very unusual if a car is stopped soon, and the fuel drain and flush that still come first sort it out.
Stories Muirton people hear about petrol in a diesel
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. A fuller tank of the same mix is all it gives, since topping up removes nothing. Percentage is not how a diesel fuel system copes with petrol, whatever that advice supposes.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the reverse. At higher pressure, through smaller parts: that's how a current diesel moves its fuel, so the lubrication matters for more, not less.
Myth: "If it starts and drives, there's no damage done." This is the one that catches people. The driver of a petrol engine fed diesel usually has no choice but to stop, since it will not run, and the harm stops with them. Feed petrol to a diesel and it normally fires up, ticks over and pulls away like nothing happened — all while its pump wears. Fine and running are not the same thing.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a separate issue. The petrol is still in that tank after that, and what it has weakened isn't put back.
Myth: "Drain the tank yourself and you are sorted." After the engine has run, some of the petrol is no longer inside the tank: it is in the filter and the fuel lines, and it goes straight back through the pump at the next start. Also, a can of petrol filled at the kerbside is genuinely dangerous.
Petrol in a diesel: how does it occur?
A careless moment is rarely the cause, and no one means to do it. A diesel nozzle mostly will not go into a petrol car, yet the slimmer petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one mistake simple, and only in one direction.
It occurs when habit and the car stop matching. A new car, a hire car or a courtesy car. A household with one petrol and one diesel on the driveway. A well-known forecourt with the pumps in a different order. Fuelling up in a hurry en route to Perth, with a train to catch. The first fill-up in a diesel Skoda Octavia after years of driving petrol is precisely the moment it takes place. Throw in a back seat full of children, a phone call or rain, and the hand wins.
Avoiding petrol in a diesel next time you fill up around Muirton
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on every forecourt. The label is what counts.
- In a vehicle you do not know, look inside the flap over the filler or at the cap before your first fill: many cars print the fuel type there.
- One of each in the home? Mark your key to your diesel — a coloured fob, a sticker — since meaning to remember isn't enough.
- "Diesel", out loud, before you lift the nozzle — every time a new or hired car gets its first tank. It seems daft. It works.
- While you are thinking about something else, this is an easy mistake to make — so put your phone away.
- Add-on devices exist for motors without one, and some diesels are built 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.
- Stop the moment you notice. Less petrol in the tank makes a weaker mixture. It does not change what to do next, which is still not to fire it up.
Muirton: already put petrol in a diesel?
Then the order of things is brief. Never fire it up, and don't switch your ignition on. The staff at the forecourt — whether at BP itself or wherever you filled up — will normally help roll it away from the petrol pump if you ask. Then phone 0333 366 0103 and tell us what was put in, roughly how much, and if it has run.
Corrosion and deposits form the issue with AdBlue, whereas petrol means lost protection. So if it was AdBlue, say so — and read its own Muirton page.
What makes one Muirton petrol in a diesel task cost more than the next
An honest single quote doesn't exist here: four scenarios, four separate tasks. What shifts the cost is chiefly which of them you are in. Where the car is counts too, and whether a van can safely reach it, after the share of petrol to what the tank takes.
Before any quote, not after, we ask three queries: the fuel that got in, its amount, and whether it's run. That's why. Given the answers, you get a straight figure instead of a range.
About Muirton and where it is
Muirton is a suburban area located on the riverside in Perth and Kinross, sitting at a low elevation of around 7 metres. Muirton is situated close to the city of Perth, approximately 1.5 miles away, and is near other local places such as Quarrymill and North Inch. Muirton has a mix of housing types, with terraced housing being predominant in the area. Muirton is part of the wider Perth urban area, with easy access to the city centre.
Muirton and Perth and Kinross: where our fuel drain cover reaches
Muirton waits in the PH postcode area, and our vans that answer petrol in diesel call-outs there work the locations around it as well — Quarrymill, North Inch and Tulloch among them. No need to move your vehicle to us. Forecourts, supermarket car parks, lay-bys and your own drive are all spots where we work.
Muirton: still at the petrol pump?
The best spot there is, then — that's where you are. Keep it off. Phone.