How Worried Should You Be? Petrol in a Diesel Car in Alloway
Not started? Then less anxious than you likely are. "Have I ruined it?" is the first thing everyone in Alloway asks, and the truthful answer is generally no, because petrol resting in a diesel tank harms nothing until it is dragged through the fuel system — by ignition priming, by the starter, or by being driven. To keep the car that way, call Petrol in Diesel then leave the engine alone. The rest of this page sets out what petrol actually does to a diesel, how to tell how far it has got, and how to make sure it doesn't happen to you a second time.
Inside your engine: what petrol in a diesel does
Passing through an engine, diesel does two jobs at once. It lubricates first, and only then does it burn. Very fine clearances are built into the injectors and the high-pressure pump, and only your diesel flowing through keeps their surfaces from grinding together.
Petrol does the first job badly and the second not at all. It's runnier than diesel and takes away the lubrication the fuel system hinges on, so a pump running on a petrol mix is a pump wearing itself. And petrol is made to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That's where the clattering comes from.
Taken together, they show what shape the problem has. Contact does not do the harm — movement does. Petrol in a tank is a fuel fault. Whatever a worn pump sheds goes on, borne by the fuel, into the injectors further along, which is why a pump that has been working on the petrol is where a mechanical problem starts.
How bad is petrol in a diesel? Four scenarios our engineers see in Alloway
Fuelled but never started — as good as it gets. The petrol is in your tank and just that tank, and the task is a drain and a flush where the car stands. This is the one scenario that can only really occur at a forecourt, as anywhere else the car has been driven to get there.
Your ignition turned on, or a short start. Once primed, your system has drawn petrol from the tank up to your filter and the fuel lines. Drain, flush, deal with the filter: still usually simple.
Driven a couple of miles. Now your pump has spent these miles labouring on thinned fuel. How hard the car was driven counts as much as how far, and this work covers that tank, the fuel lines, the fuel filter and fresh fuel through the entire circuit. A school run to the local primary school is one matter. A run as far as Glasgow, under 50 miles away, is a very different task. So is any distance on the M77, under 25 miles from Alloway, where your engine has been running hard throughout.
Driven on until it protested — clattering, smoke, a ragged idle, a soft throttle. The motor is telling you the fuel is no longer behaving like diesel. Pull up wherever you are — the verge on Cambusdoon Drive, a lay-by, a side street — then leave the car where it is. A vehicle stopped soon very seldom has long-term damage, because the drain and the flush, which still come first, deal with it.
What Alloway people get told about petrol in a diesel — and the myths in it
Myth: topping up to full with diesel makes it fine. It does not. A fuller tank of the same mixture is all it gives, because topping up takes out nothing. The assumption behind the guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Newer diesels can handle a little petrol" — a myth, and closer to the opposite. Protection counts more on current diesels, not less, because their fuel passes through smaller parts at higher pressure.
This is the one that catches people. Myth: "If it starts and drives, there's no harm done." The driver of a petrol motor fed diesel normally has no choice but to stop, because it will not run, and the damage stops there. Feed petrol to a diesel and it normally starts, idles and drives away as if nothing happened — all while its pump is wearing. A running engine does not mean fine.
An old fix for a different fault lies behind this one. Myth: "Add some two-stroke oil and drive it home." What petrol has thinned stays thinned, and the petrol remains in that tank regardless.
Once your engine has run, part of the petrol is in the filter and the lines, not your tank — and your next start pulls it right back through the pump. So the myth "drain that tank yourself and you're sorted" does not stand up. Clearing petrol into a can at the roadside is also really hazardous.
How does petrol in a diesel happen?
On purpose? Never. Through carelessness? Seldom, if ever. The forecourt makes it simple: the petrol nozzle is the slimmer of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle mostly won't go into a petrol motor at all. So the error runs one way.
It takes place when routine and the vehicle stop matching. Courtesy car, hire car, or a car that's brand new. One petrol and one diesel on the drive of the same household. The pumps in a different order on a familiar forecourt. Rushing for a train at Ayr and filling up en route. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is precisely the moment it takes place. Your hand does what it has always done when you add rain, a phone call or a back seat full of kids.
Alloway drivers: how to avoid petrol in a diesel next time
- A green handle for unleaded and black for diesel is normal in the UK — yet not on every forecourt. Trust the label on the petrol pump, not the colour.
- Plenty of cars state the fuel type inside your filler flap or on the cap, and so check there on the first fill in any car you do not know.
- Label the key. In a home with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember.
- "Diesel", out loud, before you pick up the nozzle — every time a new or hired car gets its first tank. It sounds daft. It works.
- Put the phone away. This is an easy mistake to make while you're thinking about something else.
- Some diesels come with a filler built to refuse a petrol nozzle, and devices you can add exist for vehicles without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop reading the petrol pump.
- As soon as you realise, stop: less petrol inside that tank means a weaker blend. What to do next doesn't change, though — still don't start the vehicle.
Already put petrol in a diesel around Alloway?
Then the order of things is brief. Do not crank it, and don't switch the ignition on. The attendants at the forecourt — whether at BP itself or wherever you filled up — will normally help push it away from the petrol pump if you ask. Ring 0333 366 0103 next, with three answers — your fuel, the approximate quantity, and whether it has run.
If it was AdBlue rather than petrol, say so. That is a separate issue — corrosion and deposits rather than lost lubrication — and it has its own page for Alloway.
What makes one Alloway petrol in a diesel task cost more than the next
The four situations above are four different jobs, so no single price for this would be honest. Mostly, the cost shifts with which one you are in. Next it is the ratio — how much petrol went in against how much the tank takes — and then where the car is and whether a technician can reach it safely.
Before any quote, not after, come three queries: the fuel that was put in, the amount, and if it's run. That's why. Given those replies, you get a straight figure instead of a range.
About Alloway, briefly
Alloway is a small suburban area in South Ayrshire, situated on the coast of Scotland at an elevation of 24 metres. Alloway lies near the towns of Ayr and Troon, with neighbouring areas including Belleisle, Rozelle, and Doonfoot. Alloway has a population of around 1149 people, predominantly living in detached housing. Alloway is located approximately 33 miles from Glasgow and 328 miles from London.
Alloway and South Ayrshire: where our fuel drain cover reaches
The teams answering petrol in diesel calls in Alloway, in the KA postcode area, also work the places around it, Belleisle, Rozelle and Doonfoot included. A forecourt, a supermarket car park, a lay-by or your own driveway are all places our technicians work, and the vehicle doesn't need to move to us.
Alloway: still at the petrol pump?
The best spot there is, then — that's where you are. Keep it switched off, and ring.