Should You Worry? Petrol in a Diesel Car in Otford
Likely less than you already are — as long as nobody has started the vehicle. Everyone around Otford begins with "have I wrecked it?", and the honest answer is generally no: petrol left in the tank of any diesel remains harmless until priming, cranking or driving pulls it into the system. Petrol in Diesel is who to call, with the motor left off, and so it stays that way. Further down, this page sets out what petrol really does inside a diesel, how far it may have got, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to the motor?
Passing through an engine, diesel is doing two things at once. Before it combusts, it lubricates — then it ignites. Extremely fine gaps go into the injectors and your high-pressure pump, and only the diesel flowing through keeps those surfaces from grinding together.
Petrol handles the first job badly and the second not at all. A pump working on a petrol mixture is wearing itself out, because petrol is thinner than diesel and takes away the lubrication the fuel system depends on. Petrol is also made to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that's where the rattling starts.
Put those together and the shape of the trouble is plain. The harm is done by movement, not by contact. All a tank with petrol in it amounts to is a fuel fault. After the pump has been labouring on that petrol, a mechanical problem has begun: whatever is shed by a pump that's wearing travels downstream to your injectors with your fuel.
Four scenarios we see in Otford: how bad is petrol in a diesel?
The best case there can be: filled up, never started. On a forecourt, and truly only there, the petrol is still limited to the tank — since everywhere else the car was driven to get to it. The job is draining and purging on the spot.
Ignition on, or started for a moment. Your system has been primed, and so petrol has left that tank and got to the fuel filter and your lines. Drain, flush, see to the filter: still normally easy.
Your pump has worked a few miles on diluted fuel — that is what driving it meant. Distance is only half of that; how hard it was driven counts just as much. Either way this work includes your tank, your lines, the filter and fresh fuel through the whole circuit. Driving the kids to Otford Primary School is one sort of trip. A run as far as London, under 25 miles away, is a very different task. So is any distance on the M26, under a mile from Otford, where your engine has been working hard the whole time.
It complained, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone uneven. That is the motor telling you its fuel no longer is acting like diesel. Pull up wherever you are — the verge on West High Street, a lay-by, a side street — and leave the car where it is. Lasting damage is very rare if a car is pulled over soon, and the drain and flush that still go first deal with it.
Otford motorists and the petrol in a diesel myths they hear
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. A fuller tank of the same mix is all it gives, since topping up removes nothing. That advice supposes a diesel fuel system handles petrol by percentage. It does not.
If anything, the opposite is true. Myth: "A modern diesel can cope with a bit of petrol." Protection counts more on modern diesels, not less, since their fuel passes through more precise components at higher pressure.
Myth: "If it starts and drives, there is no harm done." This is the one that fools motorists. The motorist of a petrol motor fed diesel usually has no choice but to stop, since it will not run, and the damage stops there. A diesel fed petrol generally starts, ticks over and drives away as if nothing has happened, while the pump grinds. Being able to run isn't proof of being fine.
Myth: a two-stroke additive makes it safe to drive home. It was an old workaround, meant for another issue. What petrol has diluted stays diluted, and the petrol stays inside your tank regardless.
"Drain it yourself and you are sorted" — a myth, since after it's been running some petrol sits in your filter and lines, waiting to go right back through your pump at the next start. It's also genuinely hazardous to drain petrol into a can at the kerbside.
Why petrol in a diesel takes place at all
A careless moment is rarely the cause, and no one means to do it. One way only, since of the nozzles: the smaller petrol one slides inside a diesel filler with almost no resistance, while the diesel one generally won't fit a petrol motor. That's how the forecourt makes it straightforward.
It happens when habit and your car stop matching. Any vehicle that's new to you — a hire car, on loan as a courtesy car, or brand new. A household with one petrol and one diesel on the drive. A forecourt you know, only with its pumps laid out differently. A hurried fill on the way 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 happens. Add rain, a phone call or a back seat full of children, and the hand repeats what it has always done.
Next time you fill up in Otford: preventing petrol in a diesel
- Green for unleaded and black for diesel is usual in the UK — yet not on each forecourt. Trust the label on the petrol pump, not the colour.
- Inspect the filler flap. Plenty of cars state the fuel inside the flap or on the cap. Look at it on the first fill in any motor you don't know.
- Label the key. In a house with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of intending to remember.
- It sounds daft and it does the trick: on the first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the petrol pump.
- Tuck your phone away. This is an easy mistake to make whilst you're thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler designed to block a petrol nozzle, and aftermarket devices exist for the remainder. Treat it as a backstop, then keep reading the pump.
- Less petrol means a weaker mixture, and so stop the moment you realise — while remembering that your next step is unchanged. It is still not to start the car.
Put petrol in a diesel in Otford already?
Then the order of things is brief. Leave it unstarted, with your ignition off too. Still on the forecourt, at Sainsbury's or anywhere else? Ask the staff to help you roll the car away from the petrol pump. Next, 0333 366 0103. We'll ask what got in, roughly how much, and if it's been run.
Say so if it was AdBlue rather than petrol: it is a different problem, with its own page for Otford, because AdBlue brings corrosion and deposits rather than lost lubrication.
Why one petrol in a diesel task around Otford costs more than another
Four different jobs sit behind the four situations above — which is why there is no honest single quote. Mostly, your cost shifts with which one you are in. Where your car is counts too, and whether a technician can safely reach it, after the share of petrol to what your tank takes.
What got in, how much, and if it's run — three queries our technicians ask before costing, not after, for precisely that reason. The replies turn a range into a straight figure.
About Otford itself
Otford is a village situated in the county of Kent, on the banks of the River Darent at an elevation of around 68 metres. Otford lies approximately 19 miles south-east of central London, within commuting distance of the city. Otford has a mix of old and new housing, with detached homes being the predominant type, and is surrounded by nearby places such as Twitton, Shoreham, and Dunton Green.
Across Kent and around Otford: fuel drain cover
Otford sits in the TN postcode area, and our teams that answer petrol in diesel calls there work the spots around it as well — Twitton, Shoreham and Dunton Green among them. We drain where the car is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
At the petrol pump around Otford, still?
In that case, you couldn't be in a better position. Keep it off. Call.