Keymer: Petrol in a Diesel Car? How Worried to Be
Likely less than you already are — as long as nobody has started it. Till your ignition primes your pump, the starter turns, or your car is driven, petrol in a diesel tank simply rests there and does no harm. Which makes the truthful reply to the first Keymer question — "have I ruined it?" — usually no. Leave the engine off and call Petrol in Diesel — that keeps it that way. The rest of this page explains 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 a second time.
What petrol in a diesel does to the motor
Two tasks fall to diesel on its route through a motor. It burns, and before it ignites it lubricates. Very fine clearances go into the injectors and your high-pressure pump, and only the diesel flowing through keeps those surfaces from grinding together.
The second job petrol doesn't do at all, and the first it does poorly. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump on the blend to wear itself. It's also made to resist igniting under compression — the opposite of what a diesel needs — which is where you get the clattering.
The shape of the issue is clear once you put those together. Not contact but movement is what does the damage. Petrol in a tank is a fuel problem. The start of a mechanical one is a pump that has been labouring on that petrol — and whatever a worn pump sheds moves on with your fuel to your injectors beyond it.
Four situations our technicians see around Keymer: how serious is petrol in a diesel?
Fuelled up, not once started. The best case there can be. Only the tank has petrol in it, so the job is draining that tank and flushing the fuel system where the car stands. This scenario can only really take place at a forecourt: anywhere else, the vehicle got there by being driven.
Started for a moment, or only your ignition on. With the fuel system primed, the lines and filter now hold petrol that has come from that tank. That is generally still a straightforward job — a drain, a flush, and the filter seen to.
The pump has spent a couple of miles on weakened fuel — that's what driving the car meant. Distance is only half of that; how hard it was driven counts just as much. Either way the work includes the tank, the fuel lines, your filter and fresh fuel through the entire circuit. A school run to The Windmills Junior School is one thing. Any miles on the M23, under 15 miles from Keymer, means your engine working hard throughout, and a run to Brighton and Hove, under 10 miles away, makes a very different task as well.
It protested, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone ragged. The motor is telling you your fuel is no longer behaving like diesel. Leave it where it has stopped: a lay-by, a quiet street, the verge on Ockley Lane. Lasting damage is very unusual if a vehicle is pulled over quickly, and the drain and flush that still come first deal with it.
Petrol in a diesel stories Keymer drivers hear
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." A bigger tank of the same mixture is all you get, because topping up takes out nothing. The assumption behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the opposite. At higher pressure, through finer components: that is how a newer diesel moves its fuel, so the protection matters for more, not less.
This is the one that fools motorists. Myth: "If it starts and drives, there's no harm done." Diesel in a petrol motor usually means a motor that will not run: the motorist stops, and so does the harm. While the pump wears, a diesel fed petrol usually starts, ticks over and drives away as though nothing has happened. Running doesn't mean fine.
Not so: a two-stroke additive makes it safe to drive home. It is an old workaround, meant for another issue. What petrol has weakened stays thinned, and the petrol stays in that tank regardless.
If the engine has run, part of the petrol sits in your filter and the lines, not your tank — and your next start sends it straight back through the pump. So the myth "drain your tank yourself and you're sorted" doesn't stand up. And, a can of petrol filled by the kerbside is genuinely hazardous.
How does petrol in a diesel occur?
Carelessness is seldom the cause, and nobody means to do it. The petrol nozzle is the smaller of the two and slides into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol vehicle at all. The forecourt makes it simple, and the error runs one way.
When habit and the car stop matching, it occurs. Courtesy car, hire car, or a motor that is new. One petrol and one diesel on the driveway of the same household. Your normal forecourt, its pumps suddenly in a different order. Racing for a train outside Hassocks and filling up en route. The first fill-up in a diesel BMW 3 Series after years of driving petrol is exactly the moment it takes place. Throw in a back seat full of kids, a phone call or rain, and the hand takes over.
Preventing petrol in a diesel next time you fill up in Keymer
- Green for unleaded and black for diesel is usual in the UK — yet not on every forecourt. Trust the label on the pump, not the colour.
- Check your filler flap. Plenty of vehicles state the fuel type inside the flap or on the cap. Look at it on the first fill in a motor you do not know.
- One of each in the home? Label your key to the diesel — a coloured fob, a sticker — because meaning to remember is not enough.
- Before the nozzle comes off the petrol pump the first time you fuel a hired or new motor, say "diesel" out loud. Silly, perhaps, but it works.
- Thinking about something else is when this becomes an easy mistake to make, and so tuck the phone away then keep your mind on the petrol pump.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler designed to block a petrol nozzle, and aftermarket devices are available for the remainder. Treat it as a safety net, then keep reading the petrol pump.
- The moment you notice, stop: less petrol inside the tank makes a thinner mixture. What to do next does not change, though — still do not start it.
Put petrol in a diesel in Keymer already?
Short and simple, then, is the order of things. Starting it is out, and so is switching on your ignition. Ask the staff to help you push it away from the pump if you are still on the forecourt, whether that is Esso or anywhere else. Next, 0333 366 0103. We will ask what went in, roughly how much, and if it has been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a separate problem — Keymer has a page just for it.
Keymer petrol in a diesel jobs: why one costs more than another
The four scenarios above are four different jobs, so no single quote for this would be honest. What shifts your cost is chiefly which of them you're in. Two things follow that: the petrol that was put in as a share of what that tank takes, then the place the vehicle is in and whether our van can get to it safely.
Before any quote, not after, come three questions: the fuel that was put in, the quantity, and if it has run. That is why. A range becomes a straight figure once those replies are in.
About Keymer, briefly
Keymer is a village in West Sussex, situated inland at an elevation of 56 metres, approximately 6.8 miles north of Brighton and Hove. Keymer lies near the villages of Hassocks, Ditchling, and Clayton, and is characterized by its predominantly detached housing stock. Keymer has a population of around 2136 residents, and is located about 40.4 miles south of London.
Keymer and West Sussex: where our fuel drain cover reaches
Hassocks, Ditchling and Clayton are among the locations near Keymer that the same teams work, answering petrol in diesel jobs across Keymer's BN postcode area. A forecourt, a supermarket car park, a lay-by or your own drive are all spots our engineers work, and the car doesn't need to move to us.
In Keymer and still at the petrol pump?
The best spot there is, then — that's where you are. Keep the vehicle turned off, and ring.