Petrol in a Diesel Car in The Common: How Worried Should You Be?
Not started? Then less anxious than you likely are. Petrol sitting in a diesel tank does nothing to your motor till something pulls it through the fuel system — your ignition priming your pump, your starter, or driving itself. So the fair answer to the first query anyone around The Common asks, "have I ruined it?", is usually no. To leave the car like that, phone Petrol in Diesel and leave the motor switched off. The remainder of this page covers what petrol actually does to a diesel, how to tell how far it has got, and how to make sure it does not happen to you again.
Petrol in a diesel: what does it do to the engine?
Diesel has two tasks on its way through an engine. It protects first, and after that does it burn. Extremely fine tolerances go into the injectors and your high-pressure pump, and only your diesel running through keeps their surfaces from grinding together.
Petrol does the first job badly and the second not at all. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump on the mixture wearing itself. It's also made to resist igniting under compression — the reverse of what a diesel needs — which is why you hear the clattering.
Seen together, they show the shape the problem has. Not contact but movement is what does the damage. A tank with petrol in it is a fuel problem. Whatever a worn pump sheds goes on, borne by the fuel, into your injectors downstream, which is why a pump that has worked on that petrol is where a mechanical fault begins.
Four situations our technicians see in The Common: how bad is petrol in a diesel?
Filled up, and never started: nothing beats it. The petrol is inside your tank and only your tank, and the task is a drain and a flush where the vehicle sits. This is the one situation that can only really take place at a forecourt, as anywhere else your car has been driven to get there.
Started for a second, or only your ignition on. With the fuel system primed, the fuel lines and filter now contain petrol that has come from that tank. Drain, flush, see to your filter: still usually simple.
Driven a few miles. Now your pump has spent these miles running on thinned fuel. The work is the tank, the fuel lines, your filter and clean fuel through the whole system, and how hard your car was driven matters as much as how far. On the school run to Trafalgar Community Infant School, the miles is short. A run as far as Brighton and Hove, under 25 miles away, is a very different task. So is any miles on the M23, under 10 miles from The Common, where the motor has been labouring hard throughout.
It complained, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone uneven. The engine is telling you the fuel is no longer acting like diesel. Whether it is the verge on Milnwood Road, a lay-by or a side road, stop where you are and leave it. The drain and flush-through still go first, and they take care of it: if a car is pulled over soon, long-term damage is very unusual.
Petrol in a diesel myths The Common drivers hear
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Topping up takes out nothing; it gives you a bigger tank of the same mix. A diesel fuel system does not accept petrol by percentage in the way that guidance assumes.
"Newer diesels can handle a little petrol" — a myth, and closer to the reverse. At higher pressure, through finer parts: that's how a current diesel moves its fuel, and so the lubrication counts more, not less.
The myth that catches drivers out: if it starts and drives, it must be unharmed. Diesel in a petrol motor usually means a motor that won't run: the motorist stops, and so does the harm. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually will; meanwhile the pump grinds. Running isn't the same as fine.
Myth: a two-stroke additive makes it safe to drive home. It is an old workaround, meant for another fault. What petrol has weakened stays diluted, and the petrol remains in that tank anyway.
The next start sends petrol back round the pump from your lines and the fuel filter, where some of it sits after the motor has been run. That is why a DIY tank drain does not leave you sorted — a myth. Draining petrol into a can at the roadside is also really risky.
How does petrol in a diesel happen?
It's rarely carelessness, and no one does it on purpose. One way only, since of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, while the diesel one generally won't fit a petrol vehicle. That is how the forecourt makes it straightforward.
Routine and the car getting out of step is how it takes place. Hire cars, courtesy cars, and motors that are new to you. One petrol and one diesel on the drive of the same household. A forecourt you know, but with its pumps arranged differently. A rushed fill on the way to Horsham with a train to catch. A new-to-you diesel Volkswagen Passat, its first fuelling, and a motorist accustomed to petrol: precisely when it happens. With rain, a call coming in, or a car full of children to deal with, the hand just does what it has always done.
How to prevent petrol in a diesel at your next fill-up in The Common
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most usually do. Read the pump's label; the colour is only a clue.
- Plenty of cars state the fuel inside the filler flap or on the cap, and so check it on your first fill in a vehicle you do not know.
- Good intentions count for less than a sticker or a fob in a vivid colour on the diesel's key when a house has one of each. So mark it.
- "Diesel", aloud, before you lift the nozzle — every time a new or hired car needs its first tank. It sounds daft. It works.
- Thinking about something else is when this becomes an easy mistake to make, and so tuck your phone away then keep your mind on the petrol pump.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler built to reject a petrol nozzle, and add-on devices exist for cars without one. They are a backstop, not a reason to stop reading the petrol pump.
- Spotting it halfway? Stop at once. A weaker blend results from less petrol in that tank, yet the next stage remains the same: don't fire it up.
Put petrol in a diesel around The Common already?
The order of things is brief, then. Do not switch the ignition on, and do not start it. Ask the staff to help you roll it away from the pump if you are still at the forecourt, whether that is Sainsbury's or somewhere else. Ring 0333 366 0103 next, with three answers — your fuel, the rough amount, and if it's run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost lubrication, make it a different issue — The Common has a page all for it.
The Common petrol in a diesel tasks: why one costs more than another
There's no fair single price for this, since the four situations above are four different tasks. What shifts your cost is mostly which of them you are in. Where your car is matters too, and whether a van can safely reach it, after the proportion of petrol to what that tank holds.
Three questions come first, before quoting, instead of after — what went in, how much, has it run — and this is the reason. A range becomes a straight figure once the replies are in.
About The Common and its setting
The Common is a suburban area situated on the riverside in West Sussex, with an elevation of 51 metres. The Common lies near several notable places, including Horsham, Little Haven, and Oakhill, and is within commuting distance of London, approximately 31 miles away. The Common is characterised by its predominant semi-detached housing stock and is located near the city of Brighton and Hove, about 19 miles away.
The Common and West Sussex: where our fuel drain cover runs
Horsham, Little Haven and Oakhill are among the locations around The Common that the same teams work, answering petrol in diesel call-outs across The Common's RH postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all spots we work, and the vehicle does not need to come to us.
Still at the petrol pump in The Common?
No position is better: that's where you now are. Keep it off. Ring.