Marsh: Petrol in a Diesel Car? How Worried to Be
If it has not been started, worry less than you probably are. Petrol sitting in a diesel tank does nothing to the motor till something pulls it through the system — your ignition priming your pump, the starter, or driving on its own. So the fair answer to the first question anyone in Marsh asks, "have I ruined it?", is usually no. Keep it like that: leave the motor off and call Petrol in Diesel. The remainder of this page covers what petrol really 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 your engine?
Two jobs fall to diesel on its journey through a motor. It burns, and before it burns it protects. Built to very fine gaps, the fuel injectors and your pump depend on the diesel flowing through them to keep their surfaces from wearing against one another.
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 runnier than diesel and strips out the protection your 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's where any knocking comes.
Put those together and the shape of the trouble is plain. It's movement that causes the harm, not contact. A tank with petrol in it is a fuel fault. 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 your fuel to the fuel injectors further on.
How serious is petrol in a diesel? Four situations our engineers see in Marsh
Filled up, not once started. The best case there can be. Being at a forecourt is what makes this the case: elsewhere, your car has been driven there to begin with. With the petrol kept inside that tank alone, it's drained and cleaned on the spot, and nothing more is needed.
The ignition turned on, or a short start. With the fuel system primed, the fuel lines and filter now contain petrol that came from the tank. Drain, flush, see to the fuel filter: still usually simple.
Those few miles driven were your pump labouring on fuel thinned by petrol throughout. Tank, lines, filter, then fresh fuel put through the entire system: that's this work, and the way your car was driven counts as much as the miles. On the school run to Howard Park Community School, the mileage is short. Very different a second time: a run to Bradford, under 10 miles away, or any mileage on the M62, under a mile from Marsh, where your engine never stopped running hard.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone ragged. The fuel isn't behaving like diesel any more, and the motor is saying so. Pull up where you are — on the verge on Greenside, at the kerb, down a side road — and don't move it. What comes first is still the drain and flush, and that takes care of it, with lasting damage very unusual if a car is stopped soon.
Marsh motorists and the petrol in a diesel myths they hear
Myth: topping up to full with diesel makes it fine. It doesn't. Nothing is removed by topping up — you're left with a bigger tank, still the same mix. A diesel fuel system does not tolerate petrol by percentage in the way that advice assumes.
Not so: a current diesel copes with a bit of petrol. Rather, the reverse. At higher pressure, through finer components: that is how a newer diesel handles its fuel, so the protection matters for more, not less.
One myth that catches drivers off guard: if it starts and drives, it must be unharmed. The motorist of a petrol motor fed diesel usually has no choice but to stop, since it will not run, and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile your pump grinds. A running engine doesn't mean fine.
Not so: a two-stroke additive lets you to drive home. It is an old workaround, supposed for another issue. What petrol has diluted stays thinned, and that petrol remains in your tank anyway.
Myth: "Drain the tank yourself and you're sorted." Once the motor has run, some of the petrol is no longer in the tank: it is in the fuel filter and the fuel lines, and it goes right back through your pump on your next start. And, a can of petrol filled by the roadside is truly risky.
How does petrol in a diesel take place?
No one does it on purpose, and it is rarely carelessness. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slides into a diesel filler with almost no resistance, while a diesel nozzle generally won't go into a petrol vehicle at all. So the error runs one way.
It occurs when habit and the car stop matching. Any motor that's new to you — hired, on loan as a courtesy car, or brand new. Households running one of each, petrol and diesel. The pumps in a different order on a familiar forecourt. A train to catch, and a rushed fill on the way to Low Moor. Precisely the moment it occurs: after years of driving petrol, someone fills a diesel Volkswagen Golf for the first time. Add rain, a phone call or a back seat full of kids, and the hand does what it has always done.
Preventing petrol in a diesel next time you fill up around Marsh
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on each forecourt. The label is what counts.
- Check your filler flap. Many cars state the fuel inside the flap or on the cap. Look at it on the first fill in a vehicle you don't know.
- One of each in the house? Mark the key to the diesel — a bright fob, a sticker — since intending to remember isn't enough.
- Before the nozzle comes off the petrol pump the first time you fuel a hired or new car, say "diesel" aloud. Daft, yes, yet it works.
- Mistakes like this are simple to make whilst your mind is on something else, so the phone goes away.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler built to block a petrol nozzle, and add-on devices exist for motors without one. They are a backstop, not a reason to stop reading the pump.
- Less petrol makes a weaker mixture, and so stop the moment you notice — while remembering that the next step is unchanged. It's still not to fire it up.
Marsh: already put petrol in a diesel?
Then the order of things is short. Starting it is out, and so is switching on the ignition. Ask the staff to help you push it away from the pump if you're still at the forecourt, whether that's Tesco or anywhere else. Next, 0333 366 0103. We'll ask what got in, about how much, and if it has been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a different issue — Marsh has a page just for it.
One petrol in a diesel task around Marsh costs more than another. Why?
The four situations above are four separate jobs, so no single price for this would be honest. What moves your cost is chiefly which of them you are in. After that it's the proportion — how much petrol was put in against how much that tank takes — and after that where the car is and whether our van can reach it safely.
Three queries come first, before quoting, instead of after — what was put in, how much, has it run — and this is the reason. A range turns into a straight figure when the replies are in.
About Marsh
Marsh is a suburban area in West Yorkshire, situated on the riverside at an elevation of around 80 metres. Marsh lies approximately 5 miles from Bradford and is near other local places such as Cleckheaton, Spen, and Rawfolds. Marsh has a population of around 5453 people and is characterised by predominantly terraced housing. Marsh is located about 166.8 miles north of London.
Across West Yorkshire and in Marsh: fuel drain cover
Cleckheaton, Spen and Rawfolds are among the spots near Marsh that the same vans work, answering petrol in diesel calls across Marsh's BD postcode area. The vehicle doesn't need to move to us: our engineers drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
At the petrol pump in Marsh, still?
The best place there is, then — that is where you are. Keep it off. Call.