Petrol in a Diesel Car in Carstairs: How Worried Should You Be?
Unstarted? Then less anxious than you likely feel. Everyone in Carstairs starts with "have I wrecked it?", and the fair answer is usually no: petrol left inside the tank of any diesel remains harmless till priming, cranking or driving draws it into your fuel system. Keep it like that: leave the engine off then phone Petrol in Diesel. What petrol actually does to a diesel, how to judge how far it's gone, and how to keep it from happening a second time: that is the remainder of this page.
Your engine and petrol in a diesel: what goes on
Diesel does two tasks on its way through a motor. It ignites, and before it combusts it lubricates. Made to extremely fine clearances, the injectors and the pump rely on your diesel flowing through them to keep their surfaces from wearing against one another.
The second job petrol doesn't do at all, and the first it does poorly. A pump working on a petrol mixture is wearing itself out, because petrol is thinner than diesel and strips out the lubrication the fuel system relies on. Petrol is also designed to resist igniting under compression — the reverse of what a diesel needs from its fuel — and that's where the knocking starts.
The shape of the issue is clear once you put those together. Contact does not do the harm — movement does. Petrol in the tank is a fuel fault. Once your pump has been running on that petrol, a mechanical problem has begun: anything shed by a pump that is grinding is carried onward to the injectors with your fuel.
How bad is petrol in a diesel? Four situations we see around Carstairs
Fuelled, and not started: no case is better. Just your tank has petrol in it, and so the job is emptying the tank and flushing the fuel system where the car stands. This situation can only really happen at a forecourt: anywhere else, the vehicle got there by being driven.
Started for a moment, or just the ignition on. Petrol has come out of the tank and got to the filter and the lines, because your system has been primed. Still normally easy: drain, flush, and the fuel filter seen to.
Those few miles on the road were your pump running on fuel weakened by petrol throughout. Tank, lines, filter, then clean fuel put through the entire system: that is the work, and the way the car was driven counts as much as the mileage. Driving the kids to the local primary school is one sort of trip. A run as far as Glasgow, under 25 miles away, is a very different task. So is any distance on the M74, under 10 miles from Carstairs, where the motor has been running hard the whole time.
Driven till it complained. Knocking, an uneven idle, smoke, a throttle that has gone soft. The engine is telling you the fuel is no longer acting like diesel. Stop wherever you are — the verge on West View, a lay-by, a side street — then leave the car where it is. What goes first is still the fuel drain and flush, and that deals with it, with permanent damage very rare if a vehicle is pulled over soon.
What Carstairs motorists get told about petrol in a diesel — and the stories in it
Myth: topping up to full with diesel makes it fine. It doesn't. Topping up removes nothing; it gives you a bigger tank of the same mix. A diesel fuel system doesn't tolerate petrol by percentage in the way that advice assumes.
If anything, the opposite holds. Myth: "A newer diesel can cope with a bit of petrol." A modern diesel sends its fuel through more precise parts at higher pressure, which makes the protection matter more, not less.
Myth: "If it starts and drives, there's no harm done." This is the one that catches people. Any petrol motor fed diesel normally won't run, and so the driver stops and the damage stops with them. Whilst the pump grinds, a diesel fed petrol normally starts, ticks over and drives away as if nothing has happened. Fine and running are not the same thing.
An old workaround for a separate problem lies behind this one. Myth: "Add some two-stroke oil and drive the car home." The petrol is still in your tank afterwards, and whatever it has weakened isn't put back.
The next start sends petrol back round the pump from the lines and the filter, where some of that ends up after the engine has been run. That is why draining your tank yourself doesn't leave you sorted — a myth. It's also truly hazardous to drain petrol into a can by the roadside.
Petrol in a diesel: how does it happen?
Nobody does it on purpose, and it is rarely carelessness. A diesel nozzle generally will not fit a petrol motor, but the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one error simple, and just in that direction.
When habit and the vehicle stop matching, it happens. A new motor, a hire car or a courtesy car. Two motors on one drive, one petrol, one diesel. A familiar forecourt with the pumps in a different order. Fuelling up in a rush en route to the nearest station, with a train to catch. The first fill-up in a diesel Renault Megane after years of driving petrol is precisely the moment it takes place. Your hand repeats what it has always done when you add rain, a phone call or a back seat full of children.
Next time you fill up in Carstairs: avoiding petrol in a diesel
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most generally do. Read the petrol pump's label; the colour is only a hint.
- The first fill in a strange vehicle is the time to check the filler flap — inside it, or on the cap, plenty of cars state the fuel they take.
- One of each in the home? Mark the key to your diesel — a bright fob, a sticker — since meaning to remember isn't enough.
- Before the nozzle comes off the petrol pump the first time you fill a hired or new vehicle, say "diesel" out loud. Silly, yes, yet it does the trick.
- Thinking about something else is when this becomes an easy mistake to make, so put your phone away and keep your mind on the petrol pump.
- Some diesels have a filler designed to reject a petrol nozzle, and devices you can add exist for cars without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop reading the pump.
- Stop the moment you realise. Less petrol in that tank makes a thinner mixture. It doesn't change what to do next, which is still not to fire it up.
Carstairs: already put petrol in a diesel?
Then, there's only a short order of things. Starting it is out, and so is turning on your ignition. Ask the attendants to help you roll it away from the pump if you are still at the forecourt, whether that's Lanark Loch Garage or somewhere else. Next, 0333 366 0103. We'll ask what was put in, roughly how much, and if it has been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a different problem — Carstairs has a page just for it.
Why one petrol in a diesel task around Carstairs costs more than another
There is no honest single quote for this, since the four situations above are four separate tasks. Mostly, your cost shifts with which situation you are in. Two things follow that: the petrol that was put in as a proportion of what that tank takes, then the spot the car is in and whether a van can reach it safely.
Ahead of any quote, not after, we ask three questions: the fuel that got in, the amount, and if it's run. That's why. Those answers change a range into a straight figure.
About Carstairs
Carstairs is a village in South Lanarkshire, situated on the banks of the River Clyde at an elevation of 208 metres. Carstairs has a mix of housing types, with semi-detached homes being predominant, and is located near Carstairs Junction and other small settlements like Ravenstruther and Silvermuir. Carstairs is close to Glasgow, Scotland's largest city, which is 24 miles away, and is part of the wider commuter belt around Glasgow.
Fuel drain cover across South Lanarkshire, Carstairs included
Petrol in diesel calls in Carstairs — part of the ML postcode area — go to teams that likewise cover the places around it, Carstairs Junction, Ravenstruther and Silvermuir among them. A forecourt, a supermarket car park, a lay-by or your own driveway are all spots we work, and your vehicle does not need to move to us.
Still at the pump in Carstairs?
Then you're in the best spot there can be. Turned off it stays; then ring.