Should You Worry? Petrol in a Diesel Car in Nursteed
Unstarted? Then less anxious than you likely feel. Till the ignition primes the pump, your starter turns, or the vehicle is driven, petrol in a diesel tank just waits there and does no harm. Which makes the truthful reply to the first Nursteed question — "have I ruined it?" — usually no. Petrol in Diesel is who to phone, with the engine kept off, so it stays that way. Further down, this page sets out what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you a second time.
What petrol in a diesel does to your engine
On its way through a motor, diesel does two tasks. Oiling comes before burning; it does both. What stops the surfaces inside the high-pressure pump and the fuel injectors from wearing down against each other is your diesel flowing through them — they're built to very fine clearances.
Petrol does the first job badly and the second not at all. A pump working on a petrol mixture is wearing itself out, since petrol is thinner than diesel and takes away the lubrication the fuel system depends on. Petrol is also made to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that's where the knocking starts.
Put those together and the shape of the issue is clear. It is circulation that causes the damage, not contact. Where the petrol is only inside your tank, it's a fault of fuel, nothing more. Once the pump has been working on that petrol, a mechanical fault has started: whatever is shed by a pump that is grinding is carried downstream to the fuel injectors with your fuel.
Four scenarios our engineers see around Nursteed: how serious is petrol in a diesel?
Fuelled, and not started: no case is better. Being on a forecourt is what makes this the case: elsewhere, the vehicle has been driven there to begin with. With the petrol held inside the tank alone, it is drained and rinsed right where it stands, and nothing more is needed.
Your ignition switched on, or a short start. Your system has been bled, and so petrol has left that tank and got to the filter and the lines. Normally nothing more than emptying, cleaning and sorting the fuel filter, and so still easy.
Some miles driven, and the pump has spent each of them labouring on weakened fuel. How hard the vehicle was driven matters as much as how far, and this work takes in your tank, the fuel lines, the filter and fresh fuel through the entire circuit. A school run to Southbroom St James Academy is one matter. Getting as far as Bath, under 25 miles away, makes a very different job — as does any distance on the M4, under 15 miles from Nursteed, with the engine running hard the whole time.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone uneven. The motor is telling you your fuel is no longer behaving like diesel. Leave it where it has stopped: a lay-by, a quiet street, the verge on Brickley Lane. The fuel drain and flush-through still go first, and they sort it out: if a vehicle is pulled over early, long-term damage is very uncommon.
Myths Nursteed drivers hear about petrol in a diesel
False: 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 accept petrol by percentage in the way that guidance assumes.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. At higher pressure, through more precise parts: that is how a current diesel handles its fuel, and so the lubrication counts more, not less.
"It starts, it drives, so no harm done" — the myth that trips up more motorists than any other. The motorist of a petrol engine fed diesel normally has no choice but to stop, because it will not run, and the damage stops with them. While your pump wears, a diesel fed petrol usually starts, ticks over and drives away as if nothing has happened. Fine and running aren't the same thing.
An old fix for a different problem is behind this one. Myth: "Add some two-stroke oil and drive it home." That petrol is still in your tank after that, and what it has weakened is not put back.
The next start draws petrol back round the pump out of the fuel lines and your filter, where some of it ends up after the engine has been run. That is why draining your tank yourself doesn't leave you sorted — a myth. Draining petrol into a can by the kerbside is also truly dangerous.
Why petrol in a diesel takes place so easily
No one does it on purpose, and it's rarely carelessness. The forecourt makes it easy: the petrol nozzle is the slimmer of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle generally won't go into a petrol car at all. So the slip runs one way.
The moment routine stops matching your car is the moment it takes place. A new car, a hire car or a courtesy car. Two motors on one drive, one petrol, one diesel. A forecourt you know, only with its pumps laid out differently. A train to catch, and a rushed fill on the way to Melksham. Precisely the moment it takes place: after years of driving petrol, a driver fills a diesel Volkswagen Passat for the first time. Throw in rain, a phone call or a back seat full of kids, and your hand repeats what it has always done.
Next time you fill up around Nursteed: avoiding petrol in a diesel
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most usually do. Check the petrol pump's label; the colour is only a clue.
- Inspect the filler flap. Plenty of motors state the fuel type inside the flap or on the cap. Look at it on the first fill in any motor you don't know.
- Mark the key. In a household with one of each, a coloured fob or a sticker on the 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" out loud before you take the nozzle off the petrol pump. It seems daft and it does the trick.
- Mistakes like this are straightforward to make whilst your mind is on something else, so the phone goes away.
- Add-on devices exist for motors without one, and some diesels are built with a filler that won't take a petrol nozzle. Helpful — but a backstop only, never a reason to stop checking the label.
- Less petrol makes a thinner blend, and so stop as soon as you realise — though remembering that the next stage is unchanged. It is still not to crank it.
Put petrol in a diesel around Nursteed already?
Short and simple, then, is the order of things. Leave it unstarted, with the ignition switched off too. If you are still at the forecourt — Esso or anywhere else — ask the attendants to help you roll the vehicle clear of the petrol pump. What got in, roughly how much, and whether it has run: tell us those when you phone 0333 366 0103.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a different issue — Nursteed has a page all for it.
Nursteed petrol in a diesel tasks: why one costs more than another
The four situations above are four separate tasks, so no single quote for this would be honest. Which of them you're in is mostly what shifts your cost. The ratio matters next, meaning how much of the tank is petrol, followed by the location of the car and whether getting to it is safe for a technician.
That's why our engineers ask three queries before quoting instead of after: what was put in, how much, and whether it has run. A range becomes a straight figure when the replies are in.
About Nursteed, briefly
Nursteed is a small hamlet in Wiltshire, situated inland at an elevation of around 120 metres, and is located near the larger towns of Devizes and Chippenham. Nursteed lies within commuting distance of the city of Bath, which is approximately 17 miles away. Nursteed is characterised by its predominantly detached housing stock, reflecting its rural setting. Nursteed is also close to other small settlements such as Stert and Coate.
Fuel drain cover across Wiltshire, Nursteed included
Petrol in diesel call-outs in Nursteed — part of the SN postcode area — go to teams that likewise cover the locations round it, Stert, Devizes and Coate among them. A forecourt, a supermarket car park, a lay-by or your own drive are all locations our engineers work, and your vehicle does not need to move to us.
Still at the pump in Nursteed?
Nothing beats it: that is where you now are. Keep the car turned off, then ring.