Mardy: Petrol in a Diesel Car? How Worried to Be
Less than you likely are, provided it hasn't been started. Petrol resting in a diesel tank does nothing to the motor till something draws it through the system — your ignition priming the pump, your starter, or driving on its own. So the honest answer to the first query everyone around Mardy asks, "have I wrecked it?", is usually no. To leave the vehicle like that, ring Petrol in Diesel and leave the motor switched off. Below, this page sets out what petrol really does inside a diesel, how far it might have got, and how to stop it happening to you again.
Your engine and petrol in a diesel: what goes on
Diesel has two tasks on its way through an engine. Before it combusts, it protects — then it combusts. Made to extremely fine tolerances, the injectors and your pump rely on your diesel flowing through them to keep their surfaces from wearing against one another.
Of these two jobs, petrol handles the first poorly and the second not at all. The clattering comes from petrol being made not to ignite when compressed, which is precisely the opposite of what a diesel needs. On top of that it is runnier than diesel, it strips away the lubrication the fuel system hinges on, and any pump working on such a mixture is wearing itself.
Seen together, they show what shape the issue takes. The harm is done by circulation, not by contact. Where that petrol is only in that tank, it's an issue of fuel, nothing more. Once your pump has been working on that petrol, a mechanical fault has started: whatever is shed by a pump that's grinding is carried downstream to your injectors with your fuel.
Petrol in a diesel around Mardy: how bad is it? Four situations
Filled up, not once started. The best case there is. At a forecourt, and truly only there, the petrol is still confined to your tank — since anywhere else the vehicle was driven to reach it. The job is draining and purging on the spot.
Ignition on, or started for a moment. Your system has been primed, so petrol has left your tank and reached your filter and the fuel lines. Still usually easy: drain, flush, and the filter sorted.
Those few miles on the road were the pump labouring on fuel thinned by petrol the whole way. Tank, lines, filter, then fresh fuel run through the entire system: that is the work, and the way the car was driven counts as much as the mileage. On the school run to the local primary school, the miles is small. A run as far as Newport, under 25 miles away, is a very different task. So is any distance on the M4, under 25 miles from Mardy, where your engine has been working hard throughout.
It protested, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone ragged. That is your engine telling you its fuel has stopped behaving like diesel. Whether it is the verge on Midway Lane, a lay-by or a side street, stop where you are and leave it. The fuel drain and flush-through still go first, and they deal with it: when a vehicle is pulled over soon, long-term damage is very uncommon.
What Mardy motorists get told about petrol in a diesel — and the myths in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." A fuller tank of the same mixture is all you get, because topping up removes nothing. The assumption behind that guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
Not so: a current diesel copes with a bit of petrol. Rather, the reverse. A modern diesel sends its fuel through finer components at higher pressure, which makes the protection matter more, not less.
This is the one that fools drivers. Myth: "If it starts and drives, there is no damage done." Feed diesel to a petrol motor and it usually will not run, so the driver stops — and the damage stops with them. A diesel fed petrol usually starts, ticks over and drives away as though nothing has happened, while the pump grinds. Running doesn't mean fine.
An old fix for a separate fault is behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol weakened is put back by it — and later, your tank still holds that petrol.
"Drain it yourself and you are sorted" — a myth, because after it's been running some petrol lies in your filter and lines, ready to go straight back through the pump at your next start. Clearing petrol into a can at the kerbside is also genuinely dangerous.
How it happens: petrol in a diesel
No one does it on purpose, and it's seldom carelessness. One way only, since of the nozzles: the narrower petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one generally will not fit a petrol car. That's how the forecourt makes it easy.
Routine and your car falling out of step is when it happens. A new motor, a hire car or a courtesy car. A household with one petrol and one diesel on the driveway. The pumps in a different order on a familiar forecourt. A train to catch, and a hurried fill en route to Abergavenny. 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 rain, a phone call or a back seat full of kids, and your hand repeats what it has always done.
Mardy motorists: how to prevent petrol in a diesel next time
- Read the petrol pump, not the colour. In the UK unleaded handles are generally green and diesel black, yet not on every forecourt. The label is what counts.
- Plenty of cars state the fuel type inside your filler flap or on the cap, so check it on your first fill in a car you do not know.
- A coloured fob or a sticker on the diesel's key does more than any amount of intending to remember, in a home with one of each.
- "Diesel", aloud, before you lift the nozzle — each time a new or hired car gets its first tank. It sounds daft. It does the trick.
- While you are thinking about something else, this is an easy mistake to make — so tuck the phone away.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to refuse a petrol nozzle, and add-on devices are available for the rest. Treat it as a safety net, and keep reading the petrol pump.
- Less petrol means a weaker blend, and so stop as soon as you realise — though remembering that the next stage is unchanged. It is still not to crank it.
Mardy: already put petrol in a diesel?
Then the order of things is short. Leave it unstarted, with the ignition switched off too. Ask the attendants to help you push it clear of the petrol pump if you're still at the forecourt, whether that is Esso or anywhere else. What got in, roughly how much, and if it's run: tell us that when you ring 0333 366 0103.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost protection, make it a different issue — Mardy has a page just for it.
Why one petrol in a diesel job around Mardy costs more than another
The four situations above are four separate tasks, so no single price for this would be honest. What shifts the cost is chiefly which of them you're in. The proportion matters next, meaning how much of your tank is petrol, and then the location of the vehicle and whether reaching it is safe for our van.
That is why our engineers ask three queries before costing rather than after: what was put in, how much, and whether it has run. Given those replies, you get a straight figure rather than a range.
About Mardy
Mardy is a suburban area in Monmouthshire, situated on the banks of a river at an elevation of 99 metres. Mardy lies near the towns of Abergavenny and Newport, with the communities of Llantilio Pertholey and Pen-y-Pound nearby. Mardy is characterized by its semi-detached housing stock and is located approximately 17 miles from Newport. Mardy is part of a wider residential area with a population of around 3432 people.
Fuel drain cover in Mardy and across Monmouthshire
Llantilio Pertholey, Pen-y-Pound and Abergavenny are among the spots around Mardy that the same vans work, answering petrol in diesel call-outs across Mardy's NP postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all places we drain, and your car does not need to move to us.
Still at the petrol pump around Mardy?
Nothing beats it: that's where you are. Call, and leave it switched off.