Herne Hill: Petrol in a Diesel Car? How Worried to Be
Not started? Then less worried than you probably are. Until your ignition primes your pump, your starter turns, or your car is driven, petrol in a diesel tank just waits there and does nothing. Which makes the truthful reply to the first Herne Hill query — "have I ruined it?" — normally no. To keep the vehicle like that, call Petrol in Diesel and leave the motor switched off. Further down, this page sets out what petrol actually does inside a diesel, how far it might have gone, and how to stop it happening to you a second time.
What petrol in a diesel does to the engine
Passing through a motor, diesel is doing two things at the same time. Before it combusts, it lubricates — then it combusts. What keeps the surfaces inside your high-pressure pump and the injectors from grinding against one another is the diesel passing through them — they are built to very fine tolerances.
The second task petrol does not do at all, and the first it does poorly. The clattering comes from petrol being designed not to ignite when compressed, which is exactly the reverse of what a diesel needs. On top of that it is thinner than diesel, it strips away the protection your system hinges on, and any pump working on that blend is wearing itself.
Combined, those leave the shape of the trouble plain. It's movement that causes the damage, not contact. Petrol in the tank 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 your fuel to the injectors further on.
How serious is petrol in a diesel? Four situations we see in Herne Hill
Filled up, and never started: nothing beats it. The petrol is inside the tank and just the tank, and the task is a drain and a flush where your car sits. This is the one situation that can only truly happen at a forecourt, as anywhere else your car has been driven to get there.
Started for a second, or just your ignition on. With your system primed, the lines and filter already contain petrol that came from your tank. That's generally still a simple job — a drain, a flush, and the filter seen to.
Those few miles driven meant your pump working on fuel diluted by petrol the whole way. Tank, lines, filter, then fresh fuel put through the entire circuit: that's this work, and the way the vehicle was driven counts as much as the miles. The school run to Judith Kerr Primary School is one matter. Very different once more: a trip to Westminster, under 5 miles away, or some distance on the M4, under 10 miles from Herne Hill, where the engine never stopped running hard.
Driven on until it protested — rattling, smoke, a ragged idle, a dead throttle. That is the engine telling you its fuel no longer is behaving like diesel. Pull up on the spot — on the verge on Burbage Road, at the kerb, down a side road — and don't move it again. The fuel drain and flush still go first, and they take care of it: if a vehicle is pulled over quickly, lasting damage is very unusual.
Myths Herne Hill people hear about petrol in a diesel
Myth: topping up to full with diesel makes it fine. It doesn't. Topping up takes out nothing; it gives you a bigger tank of the same mixture. Percentage isn't how a diesel fuel system tolerates petrol, whatever that guidance presumes.
Myth: a modern diesel copes with a bit of petrol. Rather, the opposite. Lubrication counts more on current diesels, not less, since their fuel passes through more precise parts at higher pressure.
The myth that catches motorists off guard: if it starts and drives, it must be unharmed. The driver of a petrol motor fed diesel usually stops, because it will not run, and the harm stops with them. Feed petrol to a diesel and it normally starts, ticks over and drives away like nothing happened — all the while its pump wears. Fine and running aren't the same thing.
An outdated workaround for a different problem lies behind this one. Myth: "Add some two-stroke oil and drive it home." What petrol has thinned stays weakened, and the petrol remains in the tank anyway.
"Drain it yourself and you're sorted" — a myth, because after it has been running some petrol lies in your filter and lines, ready to go straight back through the pump at your next start. It is also really hazardous to drain petrol into a can at the kerbside.
How petrol ends up: petrol in a diesel
It is rarely carelessness, and nobody does it on purpose. The petrol nozzle is the smaller of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol car at all. The forecourt makes it easy, and the error runs one way.
It occurs when routine and the vehicle stop matching. Hire cars, courtesy cars, and cars that are new to you. A household with one petrol and one diesel on the driveway. Your ordinary forecourt, its pumps now in a different order. Fuelling up in a hurry en route to the nearest station, with a train to catch. Years of petrol cars behind you, a diesel Volkswagen Golf in front of you on the forecourt for its first tank — that's when. Throw in a back seat full of children, a phone call or rain, and the hand wins.
Next time you fill up around Herne Hill: preventing petrol in a diesel
- Read the pump, not the colour. In the UK unleaded handles are usually green and diesel black, yet not on every forecourt. The label is what matters.
- Many cars state the fuel type inside the filler flap or on the cap, so check there on the first fill in a motor you don't know.
- Label your key. In a household with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember.
- It seems 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.
- 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 exist for cars without one, and some diesels are built with a filler that won't take a petrol nozzle. Helpful — but a backstop at best, never a reason to stop checking the label.
- Stop as soon as you realise. Less petrol in the tank means a thinner mix. It does not change what to do next, which is still not to crank it.
Already put petrol in a diesel in Herne Hill?
Short and simple, then, is the order of things. Don't turn your ignition on, and don't fire it up. If you're still at the forecourt — Texaco or anywhere else — ask the attendants to help you push it clear of the petrol pump. Then phone 0333 366 0103 and tell us what went in, about how much, and whether it has run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a separate fault — Herne Hill has a page all for it.
Herne Hill petrol in a diesel tasks: why one costs more than another
An honest single price does not exist here: four scenarios, four separate jobs. Mostly, the cost moves with which situation you're in. Beyond that it is the ratio — how much petrol was put in against how much that tank takes — and then where the car is and whether a van can reach it safely.
Ahead of any quote, not after, we ask three queries: the fuel that went in, the amount, and whether it's run. That's why. A range turns into a straight figure when the answers are in.
About Herne Hill, for a moment
Herne Hill is a suburban area in south London, situated approximately 4.1 miles from central London and 3.6 miles from Westminster. Herne Hill is characterised by its predominantly terraced housing and is located near several notable areas, including Brockwell Park and Dulwich Village. Herne Hill sits at an elevation of around 24 metres, and its population is approximately 9878 residents. Herne Hill is also close to Knights Hill, another nearby suburban area.
Fuel drain cover around Herne Hill and across Greater London
Petrol in diesel call-outs in Herne Hill — part of the SE postcode area — go to teams that likewise cover the spots around it, Brockwell Park, Knights Hill and Dulwich Village included. You need not move your car to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all places we drain.
In Herne Hill and still at the petrol pump?
Then, you could not be in a better place. Keep it off. Phone.