Central Parade: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less anxious than you likely are. Petrol sitting in a diesel tank does nothing to the motor until something pulls it through the fuel system — the ignition priming the pump, your starter, or the drive itself. So the honest answer to the first query anyone in Central Parade asks, "have I ruined it?", is usually no. Keep it that way: leave the motor off then ring Petrol in Diesel. The remainder 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 again.
What petrol in a diesel does to the motor
Passing through an engine, diesel does two things at once. Before it combusts, it protects — and then it ignites. The high-pressure fuel pump and the injectors are made to extremely fine gaps, and your diesel passing through them is what keeps those surfaces from wearing down against one another.
Of those two jobs, petrol manages the first badly and the second never. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump on the blend wearing itself. It's equally made to resist igniting under compression — the opposite of what a diesel needs — which is where you hear the clattering.
Put these together and the shape of the issue is plain. Contact doesn't do the harm — movement does. All a tank with petrol in it amounts to is a fuel fault. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with the fuel to the fuel injectors downstream.
Four scenarios we see around Central Parade: how serious is petrol in a diesel?
Fuelled but not once started — the best it gets. At a forecourt, and truly only there, the petrol is still limited to your tank — because anywhere else the car was driven to get to it. The job is emptying and purging on the spot.
A brief spell of running, or just your ignition on. The system has been primed, and so petrol has left your tank and reached the filter and the fuel lines. Usually little more than emptying, flushing and seeing to the filter, so still straightforward.
A few miles driven, and your pump has spent every one of them labouring on thinned fuel. How hard your car was driven counts as much as how far, and this work covers that tank, the lines, the fuel filter and clean fuel through the entire system. On the school run to Emmanuel Community School, the distance is small. Any distance on the M11, under 3 miles from Central Parade, means your engine has worked hard throughout, and a run to London, under 10 miles away, is a very different job as well.
Driven on until it complained — knocking, smoke, an uneven idle, a soft throttle. That is your engine telling you its fuel no longer is behaving like diesel. Whether it is the verge on Hoe Street, a lay-by or a side street, stop where you are and leave it. What comes first is still the fuel drain and flush-through, and that deals with it, with lasting damage very rare when a vehicle is pulled over early.
Central Parade drivers and that petrol in a diesel myths they hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. Nothing comes out when you top up — the tank just holds more of the same mixture. The idea behind the advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
If anything, the reverse is true. Myth: "A current diesel can cope with a bit of petrol." Lubrication matters more on modern diesels, not less, since their fuel runs through more precise parts at higher pressure.
This is the one that catches drivers. Myth: "If it starts and drives, there is no harm done." The driver of a petrol motor fed diesel normally stops, since it will not run, and the damage stops there. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually will; meanwhile your pump grinds. Being able to run isn't proof of being fine.
An outdated fix for a separate problem is behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." The petrol is still in the tank after that, and whatever it has weakened isn't put back.
Once the motor has run, part of that petrol is in the fuel filter and the fuel lines, not that tank — and the next start sends it right back through the pump. So the myth "drain your tank yourself and you're sorted" doesn't stand up. Emptying petrol into a can by the roadside is also genuinely dangerous.
How it happens: petrol in a diesel
Nobody does it on purpose, and it's seldom carelessness. The petrol nozzle is the narrower of the two and slips into a diesel filler with almost no resistance; a diesel nozzle generally will not go into a petrol vehicle at all. The forecourt makes it easy, and the mistake runs one way.
The moment habit stops matching the vehicle is the moment it occurs. Hire cars, courtesy cars, and cars that are new to you. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a well-known forecourt. Racing for a train at Walthamstow Central and filling up en route. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is exactly the moment it happens. Add rain, a phone call or a back seat full of kids, and the hand does what it has always done.
How to prevent petrol in a diesel at your next fill-up in Central Parade
- A green handle for unleaded and black for diesel is usual in the UK — but not on every forecourt. Go by the label on the petrol pump, not the colour.
- Many cars state the fuel inside your filler flap or on the cap, so check there on your first fill in any motor you don't know.
- One of each in the house? Label your key to your diesel — a bright fob, a sticker — because meaning to remember isn't enough.
- "Diesel", aloud, before you pick up the nozzle — every time a new or hired car gets its first tank. It sounds daft. It works.
- While you're thinking about something else, this is an easy mistake to make — so put the phone away.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler designed to block a petrol nozzle, and add-on devices are available for cars without one. They are a backstop, not a reason to stop checking the pump.
- As soon as you notice, stop: less petrol in that tank makes a thinner mixture. What to do next doesn't change, though — still do not start the car.
Already put petrol in a diesel around Central Parade?
Then, there is only a short order of things. Leave it unstarted, with your ignition off too. Yet on the forecourt, at BP or anywhere else? Ask the staff to help you roll it clear of the petrol pump. Then call 0333 366 0103 and tell us what got in, roughly how much, and if it has run.
If it was AdBlue instead of petrol, say so. That's a separate issue — corrosion and deposits rather than lost lubrication — and it has its own page for Central Parade.
Why one petrol in a diesel job in Central Parade costs more than another
Four separate tasks lie behind the four situations above — which is why there is no honest single price. Mostly, the cost moves with which situation you're in. Where the car is matters too, and whether a technician can safely reach it, after the ratio of petrol to what the tank holds.
Three queries come first, before quoting, rather than after — what was put in, how much, has it run — and this is the reason. Given those replies, you get a straight figure rather than a range.
About Central Parade and its setting
Central Parade is a locality in the London Borough of Waltham Forest, situated approximately 7 miles northeast of central London. Central Parade sits at an elevation of around 34 metres, in a densely populated area with a high proportion of flat dwellings. Central Parade is close to nearby places such as Walthamstow Village and Upper Walthamstow, and is part of the larger Walthamstow area.
Fuel drain cover in Central Parade and across Greater London
Walthamstow Village, Upper Walthamstow and Walthamstow are among the spots around Central Parade that the same vans work, answering petrol in diesel call-outs across Central Parade's E postcode area. Our engineers drain where your vehicle is — your own drive, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
Still at the pump in Central Parade?
Then you're in the best spot there can be. Ring, and leave it turned off.