Braco: Petrol in a Diesel Car? How Worried to Be
Likely less than you are now — provided no one has started it. Everyone around Braco starts with "have I wrecked it?", and the fair answer is generally no: petrol resting in the tank of a diesel remains harmless until priming, cranking or driving draws it into the fuel system. Keep it that way: leave the motor off then call Petrol in Diesel. The rest of this page sets out what petrol really does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
What petrol in a diesel does to the engine
Passing through an engine, diesel is doing two things at once. It combusts, and before it combusts it protects. The high-pressure fuel pump and your injectors are designed to extremely fine gaps, and the diesel passing through them is what keeps those surfaces from wearing down against one another.
Of these two jobs, petrol manages the first poorly and the second never. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, leaving 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 why you get the knocking.
The shape of the trouble is clear once you put those together. It is circulation that causes the damage, not contact. A tank with petrol in it is a fuel fault. After your pump has been labouring on that petrol, a mechanical issue has begun: whatever is shed by a pump that is wearing is carried downstream to your injectors with your fuel.
Four situations our engineers see around Braco: how serious is petrol in a diesel?
The best case there is: filled up, not once started. The petrol is in the tank and just the tank, and the job is a drain and a flush where the car sits. This is the one situation that can only really occur at a forecourt, as anywhere else the car has been driven to get there.
A moment's running, or just the ignition on. With the system primed, the lines and filter now hold petrol that came from that tank. Drain, flush, deal with your filter: still usually straightforward.
Your pump has worked a couple of miles on diluted fuel — that is what driving it does. Distance is only half of that; how hard it was driven counts equally. Either way the work includes your tank, the lines, the fuel filter and clean fuel through the whole circuit. On the school run to the local primary school, the miles is small. Driving as far as Stirling, under 15 miles away, makes a very different task — as does any distance on the M9, under 10 miles from Braco, with your engine running hard all the way.
Driven till it complained. Clattering, an uneven idle, smoke, a throttle that has gone soft. What you are hearing is your engine signalling fuel that no longer runs like diesel. Pull up where you are — on the verge on Grinnan Road, at the kerb, down a side road — and don't move it again. A car pulled over early very rarely has lasting damage, because the drain and the flush, which still come first, sort it out.
Myths Braco people hear about petrol in a diesel
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 bigger tank of the same mixture. A diesel fuel system does not accept petrol by percentage in the way that guidance supposes.
"Current diesels can handle a little petrol" — a myth, and closer to the reverse. At higher pressure, through smaller parts: that is how a current diesel moves its fuel, and so the lubrication matters for more, not less.
"It starts, it drives, and so there is no harm" — the myth that catches most people than any other. Feed diesel to a petrol motor and it normally will not run, so the motorist stops — and the damage stops with them. A diesel fed petrol generally starts, idles and drives away as if nothing has happened, while your pump grinds. Fine and running are not the same at all.
Myth: "Add some two-stroke oil and drive it home." It's an old fix for a distinct problem. None of what petrol thinned gets put back by it — and later, that tank still contains the petrol.
"Drain it yourself and you are sorted" — a myth, because after it's been running some petrol lies in the fuel filter and lines, waiting to go straight back through the pump on your next start. It's also genuinely hazardous to drain petrol into a can at the roadside.
How petrol ends up: petrol in a diesel
A careless moment is seldom the cause, and no one means to do it. A diesel nozzle generally won't fit a petrol car, but the slimmer petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one error straightforward, and only in that direction.
When habit and the car stop matching, it happens. Hire cars, courtesy cars, and cars that are new to you. A household with one petrol and one diesel on the driveway. A well-known forecourt with the pumps in a different order. A train to catch, and a rushed fill en route to Gleneagles. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is precisely the moment it occurs. Add a back seat full of kids, a phone call or rain, and habit wins.
Braco drivers: how to avoid petrol in a diesel next time
- A green handle for unleaded and black for diesel is normal in the UK — but not on each forecourt. Go by the label on the petrol pump, not the colour.
- In a vehicle you do not know, look inside the flap over your filler or at the cap before the first fill: plenty of vehicles print the fuel there.
- Good intentions count for less than a sticker or a fob in a bright colour on the diesel's key if a house has one of each. So mark it.
- It seems silly and it does the trick: on the first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the petrol pump.
- Thinking about something else is when this becomes an easy mistake to make, so put the phone away then keep your mind on the petrol pump.
- Add-on devices are available for vehicles without one, and some diesels are built with a filler that will not take a petrol nozzle. Helpful — but a safety net at best, never a reason to stop checking the label.
- As soon as you realise, stop: less petrol in your tank makes a thinner mix. What to do next does not change, though — still do not start the car.
Braco: already put petrol in a diesel?
Then, there's only a short order of things. Leave it unstarted, with the ignition off too. If you are still at the forecourt — Shell or anywhere else — ask the staff to help you roll the vehicle clear of the pump. Next, 0333 366 0103. We'll ask what went in, about how much, and if it's been run.
Corrosion and deposits are the trouble with AdBlue, where petrol brings lost lubrication. So if it was AdBlue, say so — and read its own Braco page.
Braco petrol in a diesel jobs: why one costs more than another
An honest single quote does not exist here: four scenarios, four separate jobs. What moves the cost is mostly which of them you are in. The ratio counts next, meaning how much of that tank is petrol, followed by the position of the vehicle and whether reaching it is safe for a technician.
Before any quote, not after, we ask three questions: the fuel that got in, its volume, and if it has run. That is why. The answers turn a range into a straight figure.
About Braco and where it is
Braco is a small village situated on the banks of a river in Perth and Kinross, with a mix of rural and residential areas. Braco sits at an elevation of 119 metres, surrounded by rolling countryside and nearby settlements like Dunduff and Greenloaning. Braco is located near the city of Stirling, approximately 10.5 miles away, and is characterized by its predominantly detached housing stock. Braco has a population of around 568 people, according to recent estimates.
Across Perth and Kinross and around Braco: fuel drain cover
Petrol in diesel calls around Braco — part of the FK postcode area — go to vans that likewise cover the places about it, Dunduff, Greenloaning and Newton of Buttergrass included. Our technicians drain wherever your vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
Braco: still at the petrol pump?
The best position there is, then — that's where you are. Turned off it stays; then ring.