Petrol in a Diesel Car in Coombe: How Worried Should You Be?
Unstarted? Then less worried than you probably feel. Until the ignition primes your pump, your starter cranks, or your vehicle is driven, petrol in a diesel tank simply sits there and does no harm. Which means the truthful reply to the first Coombe question — "have I wrecked it?" — normally no. Petrol in Diesel is who to ring, with your engine left off, and so it remains that way. Below, you will find what petrol actually does inside a diesel, how far it might have got, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to your engine?
On its way through a motor, diesel has two tasks. Lubricating comes before burning; it does both. Made to very fine clearances, the fuel injectors and your pump rely on the diesel flowing through them to keep their surfaces from wearing against one another.
The second task petrol doesn't do at all, and the first it does poorly. A pump working on a petrol blend is wearing itself out, since petrol is thinner than diesel and strips out the protection your fuel system depends on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that's where the rattling starts.
The shape of the trouble is clear once you put those together. Not contact but circulation is what causes the damage. Petrol in a tank is a fuel fault. A pump that has been working on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the injectors further on.
Coombe, petrol in a diesel: four cases, from mild to major
The best case there can be: filled up, not once started. Being on a forecourt is what makes this possible: elsewhere, the car has been driven there to begin with. With the petrol held inside that tank alone, it is drained and flushed right where it stands, and nothing more is needed.
Started for a moment, or only the ignition on. With the fuel system primed, your lines and filter now hold petrol that came from your tank. That is normally still an easy task — a drain, a flush, and the filter seen to.
A couple of miles driven, and your pump has spent each of them labouring on weakened fuel. Tank, lines, filter, then fresh fuel run through the whole circuit: that's the work, and the way your car was driven counts as much as the distance. On the school run to Coombe Hill Infant School, the miles is small. Very different a second time: a trip to Westminster, under 10 miles away, or some mileage on the M4, under 10 miles from Coombe, where your engine kept working hard.
Driven on until it protested — knocking, smoke, a ragged idle, a soft throttle. The motor is telling you the fuel is no longer acting like diesel. Pull up where you are — on the verge on Coombe Lane West, at the kerb, down a side road — and don't move it again. What goes first is still the fuel drain and flush-through, and that takes care of it, with permanent damage very uncommon if a car is stopped soon.
What Coombe drivers get told about petrol in a diesel — and the myths in it
False: topping up to full with diesel makes it fine. It does not. Topping up removes nothing; it gives you a bigger tank of the same mix. The assumption behind the guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Newer diesels can handle a little petrol" — a myth, and nearer the reverse. Finer components and higher pressure are how a newer diesel runs its fuel, and that makes the protection matter more, not less.
This is the one that catches motorists. Myth: "If it starts and drives, there's no damage done." Any petrol engine fed diesel usually won't run, and so the driver stops and the damage stops with them. A diesel fed petrol generally starts, idles and drives away as if nothing has happened, whilst the pump grinds. Fine and running are not the same at all.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an old fix for a different issue. The petrol is still inside that tank after that, and what it has weakened isn't put back.
Myth: "Drain your tank yourself and you're sorted." Once the engine has been run, some of that petrol is no longer inside the tank: it's in the fuel filter and your lines, and it goes straight back through your pump on the next start. Clearing petrol into a can by the roadside is also genuinely dangerous.
Petrol in a diesel: how does it happen?
Nobody does it on purpose, and it's rarely 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 simple, and the slip runs one way.
It occurs when habit and the car stop matching. A new motor, a hire car or a courtesy car. One petrol and one diesel on the driveway of the same household. Your ordinary forecourt, its pumps suddenly in a different order. Rushing for a train at New Malden and filling up en route. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is precisely the moment it occurs. Throw in rain, a phone call or a back seat full of children, and your hand repeats what it has always done.
How to prevent petrol in a diesel at your next fill-up around Coombe
- The label is what counts, so read the pump rather than the colour: in the UK unleaded handles are normally green and diesel black, yet not on every forecourt.
- Plenty of cars state the fuel inside your filler flap or on the cap, and so check it on the first fill in any vehicle you do not know.
- One of each in the house? Mark the key to your diesel — a coloured fob, a sticker — since meaning to remember is not enough.
- "Diesel", out loud, before you lift the nozzle — each time a new or hired car needs its first tank. It seems silly. It works.
- Put your phone away. This is an easy mistake to make whilst you are thinking about something else.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler built to reject a petrol nozzle, and add-on devices are available for motors without one. They are a backstop, not a reason to stop reading the pump.
- Noticing it halfway? Stop at once. A thinner blend follows from less petrol in that tank, yet the next stage stays the same: don't fire it up.
Already put petrol in a diesel around Coombe?
Then the order of things is brief. Do not fire it up, and don't switch your ignition on. If you are still at the forecourt — Esso or anywhere else — ask the staff to help you push the vehicle away from the pump. What got in, about how much, and whether it has run: tell us those when you ring 0333 366 0103.
Corrosion and deposits are the trouble with AdBlue, whereas petrol means lost protection. So if it was AdBlue, say so — and read its own Coombe page.
Why one petrol in a diesel task in Coombe costs more than another
There's no fair single quote for this, since the four situations above are four different tasks. What shifts the cost is mostly which of them you are in. The proportion counts next, meaning how much of your tank is petrol, and then the position of the car and whether reaching it is safe for a van.
What was put in, how much, and whether it's run — three queries our technicians ask before costing, not after, for precisely that reason. A range turns into a straight figure once those replies are in.
About Coombe, briefly
Coombe is a suburban area in southwest London, situated approximately 8.5 miles from central London. Coombe sits at an elevation of around 45 metres, near the neighbouring areas of Copse Hill, Kingston Vale, and Kingston Hill. Coombe is characterized by its predominantly detached housing stock, which reflects the area's residential nature. Coombe has a population of around 2670 people, according to recent estimates.
Fuel drain cover in Coombe and across Greater London
Coombe sits in the KT postcode area, and the vans that answer petrol in diesel calls there work the places near it as well — Copse Hill, Kingston Vale and Kingston Hill among them. We drain where your vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
At the pump in Coombe, right now?
Then you're in the best position there is. Leave the car turned off, then ring.