Petrol in a Diesel Car in Laleham: How Worried Should You Be?
Probably less than you already are — provided nobody has started it. Petrol sitting in a diesel tank does nothing to the engine until something pulls it through the system — the ignition priming your pump, your starter, or the drive on its own. So the honest answer to the first query everyone around Laleham asks, "have I wrecked it?", is generally no. Petrol in Diesel is who to phone, with your motor kept off, and so it stays that way. The remainder of this page explains what petrol really does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
The engine and petrol in a diesel: what happens
Passing through an engine, diesel is doing two jobs at once. Before it burns, it lubricates — then it combusts. What stops the surfaces inside the high-pressure pump and your injectors from grinding against each other is your diesel flowing through them — they are built to extremely fine tolerances.
Badly at the first, not at all at the second: that is petrol. 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 relies on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that is where the knocking comes.
Taken together, they make clear what shape the problem takes. Not contact but circulation is what does the damage. A tank with petrol in it is a fuel issue. A pump that has been labouring on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with the fuel to the fuel injectors downstream.
Four situations we see around Laleham: how bad is petrol in a diesel?
Fuelled, and never started: nothing beats it. On a forecourt, and truly only there, the petrol is still confined to the tank — because anywhere else the car was driven to get to it. The job is emptying and rinsing on the spot.
Ignition on, or started for a second. With your system primed, your lines and filter now hold petrol that has come from that tank. Usually nothing more than draining, flushing and seeing to your filter, and so still simple.
The pump has worked a couple of miles on diluted fuel — that's what driving it does. The work is that tank, your lines, the fuel filter and fresh fuel through the whole circuit, and how hard the vehicle was driven matters as much as how far. A school run to Laleham CofE VA Primary School is one matter. Getting as far as Westminster, under 25 miles away, makes a very different job — as does any distance on the M3, under 3 miles from Laleham, with the engine working hard all the way.
It complained, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone ragged. The fuel is not behaving like diesel any more, and your motor is saying so. Leave it where it stops: a lay-by, a quiet street, the verge on Staines Road. The fuel drain and flush-through still come first, and they take care of it: if a car is stopped soon, lasting damage is very rare.
Petrol in a diesel myths Laleham drivers hear
"Top it up the rest of the way with diesel and it will be fine" — a myth. It will not. Nothing is removed by topping up — you are left with a bigger tank, still the same mix. That advice presumes a diesel fuel system tolerates petrol by percentage. It does not.
"Newer diesels can handle a little petrol" — a myth, and nearer the reverse. More precise components and higher pressure are the way a current diesel runs its fuel, and that makes the lubrication count more, not less.
"It starts, it drives, and so there is no harm" — the myth that trips up most people than any other. Feed diesel to a petrol motor and it generally will not run, and so the motorist stops — and the harm stops with them. Feed petrol to a diesel and it normally fires up, ticks over and drives away as if nothing happened — all while its pump is wearing. A running engine does not mean fine.
Myth: "Add some two-stroke oil and drive the car home." It is an old fix for a different fault. None of what petrol diluted is put back by it — and later, that tank still holds that petrol.
"Drain it yourself and you are sorted" — a myth, since after it's been running some petrol lies in the fuel filter and lines, waiting to go straight back through your pump on your next start. Draining petrol into a can at the roadside is also really risky.
Petrol in a diesel: how does it occur?
Carelessness is seldom the cause, and no one means to do it. The forecourt makes it simple: the petrol nozzle is the narrower of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle mostly will not go into a petrol car at all. So the slip runs one way.
Habit and the vehicle getting out of step is when it occurs. Hire cars, courtesy cars, and vehicles that are new to you. A household with one petrol and one diesel on the drive. A forecourt you know, only with its pumps laid out differently. A rushed fill en route to Staines with a train to catch. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is precisely the moment it occurs. Add rain, a phone call or a back seat full of kids, and the hand does what it has always done.
How to avoid petrol in a diesel on your next fill-up in Laleham
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, but not on each forecourt. The label is what counts.
- Check your filler flap. Many vehicles state the fuel type inside the flap or on the cap. Look at it on your first fill in any car you don't know.
- Mark the 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 intending to remember.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the pump. It sounds daft and it works.
- Whilst you are thinking about something else, this is an easy mistake to make — so tuck your phone away.
- Some diesels have a filler designed to refuse a petrol nozzle, and devices you can add exist 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 the moment you notice. Less petrol inside that tank makes a weaker mixture. It does not change what to do next, which is still not to start the car.
Petrol already in a diesel in Laleham? Start here
In that case, there is just a short order of things. Leave it unstarted, with your ignition switched off too. If you're still on the forecourt — Asda or anywhere else — ask the staff to help you roll the car clear of the petrol pump. What went in, about how much, and whether it's run: tell us those when you phone 0333 366 0103.
Corrosion and deposits form the issue with AdBlue, where petrol brings lost protection. So if it was AdBlue, say so — and read its own Laleham page.
One petrol in a diesel task in Laleham costs more than another. Why?
Four different tasks sit behind the four situations above — which is why there's no honest single quote. The situation itself does most of the work of moving your cost. Two things come after that: the petrol that got in as a share of what that tank takes, then the spot the car is in and whether a technician can get to it safely.
Ahead of any quote, not after, we ask three questions: your fuel that was put in, its amount, and whether it's run. That is why. With those answers, you get a straight figure rather than a range.
About Laleham and its setting
Laleham is a small village in Surrey, situated on the River Thames at an elevation of around 15 metres. Laleham lies on the southwestern outskirts of Greater London, approximately 17 miles from the city centre. Laleham has a mix of old and new housing, with detached homes being the predominant type, and is close to nearby places such as Penton Hook and Abbey Mead. Laleham is a relatively small community with a population of around 541 people.
Across Surrey and around Laleham: fuel drain cover
Laleham waits in the TW postcode area, and our teams that answer petrol in diesel jobs there work the locations around it as well — Penton Hook, Abbey Mead and Littleton among them. We drain wherever your car 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 around Laleham?
Then you're in the best spot there can be. Ring, and leave it turned off.