Kettlebridge: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less anxious than you probably feel. "Have I ruined it?" is the first thing anyone in Kettlebridge asks, and the honest answer is generally no, since petrol resting in a diesel tank hurts nothing till it's drawn through the fuel system — by ignition priming, by the starter, or by being driven. Keep it that way: leave the engine off and ring Petrol in Diesel. What petrol actually does to a diesel, how to gauge how far it's gone, and how to stop it from happening a second time: that's the remainder of this page.
What petrol in a diesel does to the motor
Passing through a motor, diesel is doing two jobs at once. It protects first, and after that does it burn. Very fine clearances are built into the injectors and the high-pressure fuel pump, and just your diesel running through keeps those surfaces from grinding together.
The second job petrol does not do at all, and the first it does badly. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump on the blend wearing itself. It is also 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 trouble is clear. Not contact but circulation is what does the harm. Where that petrol is only inside the tank, it is a problem of fuel, nothing more. Whatever a worn pump sheds travels on, carried by the fuel, into the fuel injectors downstream, which is why a pump that has worked on the petrol is where a mechanical problem begins.
Petrol in a diesel around Kettlebridge: how bad is it? Four cases
Filled but never started — the best it gets. At a forecourt, and really only there, the petrol is still limited to the tank — because anywhere else the car was driven to reach it. The job is draining and purging on the spot.
Ignition on, or started for a moment. Petrol has come out of that tank and got to your filter and the lines, because the fuel system has been primed. Usually nothing more than emptying, purging and seeing to the fuel filter, and so still easy.
Your pump now spent a few miles on diluted fuel — that's what driving the vehicle meant. How hard the car was driven matters as much as how far, and this work covers your tank, the lines, your filter and clean fuel through the entire system. On the school run to the local primary school, the miles is small. A run as far as Dundee, under 25 miles away, is a very different task. So is any distance on the M90, under 10 miles from Kettlebridge, where your engine has been working hard the whole time.
Driven till it protested. Knocking, a lumpy idle, smoke, a throttle that has gone soft. That is the engine telling you its fuel has stopped behaving like diesel. Leave it wherever it stops: a lay-by, a quiet street, the verge on Haughfield Terrace. A vehicle pulled over soon very rarely has permanent damage, because the fuel drain and the flush-through, which still come first, deal with it.
Myths Kettlebridge motorists hear about petrol in a diesel
False: topping up to full with diesel makes it fine. It doesn't. A bigger tank of the same mix is all it gives, because topping up removes nothing. The assumption behind that advice — that diesel fuel systems accept petrol by percentage — is wrong.
Not so: a newer diesel copes with a bit of petrol. If anything, the reverse. At higher pressure, through finer parts: that's how a current diesel handles its fuel, so the lubrication matters for more, not less.
"It starts, it drives, and so no harm done" — the myth that catches more people than any other. Feed diesel to a petrol engine and it normally won't run, so the motorist stops — and the harm stops with them. A diesel fed petrol normally starts, ticks over and drives away as if nothing has happened, whilst the pump wears. Being able to run is not proof of being fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a different issue. It doesn't put back what petrol has thinned, and that petrol is still in the tank after that.
The next start draws petrol back round the pump out of the lines and the filter, where some of it ends up once the engine has been run. That's why draining your tank yourself does not leave you sorted — a myth. And, a can of petrol filled at the roadside is truly dangerous.
How petrol ends up: petrol in a diesel
On purpose? Never. Through carelessness? Rarely, if ever. The petrol nozzle is the slimmer of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol car at all. The forecourt makes it simple, and the slip runs one way.
The moment routine stops matching the car is the moment it occurs. A new motor, a hire car or a courtesy car. Two motors on one drive, one petrol, one diesel. A forecourt you know, only with its pumps laid out differently. A train to catch, and a rushed fill en route to Ladybank. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is precisely the moment it happens. With rain, a call arriving, or children to deal with, the hand simply does what it always has.
Kettlebridge people: how to avoid petrol in a diesel next time
- Green for unleaded and black for diesel is usual in the UK — but not on each forecourt. Go by the label on the pump, not the colour.
- Inspect your filler flap. Many vehicles state the fuel inside the flap or on the cap. Look at it on your first fill in a vehicle you don't know.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of intending to remember, for a house with one of each.
- It sounds daft and it works: on your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the pump.
- Mistakes like this are simple to make whilst your mind is on something else, and so your phone goes away.
- Some diesels have a filler designed to refuse a petrol nozzle, and devices you can add are available for motors without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop reading the petrol pump.
- Stop as soon as you notice. Less petrol in the tank makes a thinner mix. It does not change what to do next, which is still not to fire it up.
Put petrol in a diesel in Kettlebridge already?
Then the order of things is short. Don't fire it up, and do not turn the ignition on. Ask the attendants to help you roll it clear of the petrol pump if you are still at the forecourt, whether that's BP or anywhere else. What got in, about how much, and if it's run: tell us those when you ring 0333 366 0103.
Corrosion and deposits form the issue with AdBlue, where petrol brings lost protection. So if it was AdBlue, say so — and see its own Kettlebridge page.
Why one petrol in a diesel task in Kettlebridge costs more than another
There is no honest single price for this, since the four situations above are four different jobs. What shifts the cost is chiefly which of them you're in. The ratio matters next, meaning how much of that tank is petrol, followed by the location of the car and whether getting to it is safe for a van.
What was put in, how much, and if it's run — three questions our technicians ask before pricing, not after, for exactly that reason. A range becomes a straight figure once the answers are in.
About Kettlebridge, for a moment
Kettlebridge is a small village in Fife, situated on the banks of a river at an elevation of 47 metres. Kettlebridge lies near the towns of Kingskettle and Balmalcolm, and is approximately 15 miles from Dundee. Kettlebridge has a population of around 504 people, predominantly living in semi-detached housing. Kettlebridge is located in a scenic area, with the city of Dundee and the countryside of Fife nearby.
Across Fife and around Kettlebridge: fuel drain cover
Kingskettle, Balmalcolm and Monkstown are among the places around Kettlebridge that the same vans work, answering petrol in diesel jobs across Kettlebridge's KY postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all places our technicians work, and your vehicle doesn't need to come to us.
In Kettlebridge and still at the petrol pump?
Then you are in the best position there can be. Switched off it remains; then ring.