Petrol in a Diesel Car in Lower Town: How Worried Should You Be?
Provided it has not been started, you can worry less than you probably are. Petrol sitting in a diesel tank does nothing to the motor until something pulls it through the system — your ignition priming your pump, the starter, or the drive on its own. So the honest answer to the first query everyone in Lower Town asks, "have I ruined it?", is generally no. To keep it that way, phone Petrol in Diesel then leave the engine switched off. Further down, you will find what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you again.
The engine and petrol in a diesel: what goes on
On its way through a motor, diesel does two tasks. It protects to begin with, and after that does it burn. Very fine clearances are built into the injectors and the high-pressure fuel pump, and only your diesel flowing through keeps their surfaces from grinding together.
The second task petrol doesn't do at all, and the first it does poorly. It is thinner than diesel and strips away the lubrication your fuel system depends on, so a pump running on a petrol mixture is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That's where the knocking comes from.
Seen together, they make clear the shape the trouble has. It's circulation that causes the harm, not contact. Petrol in the tank is a fuel issue. Whatever a worn pump sheds travels on, carried by your fuel, into the fuel injectors downstream, which is why a pump that has worked on the petrol is where a mechanical fault begins.
Four scenarios our technicians see in Lower Town: how bad is petrol in a diesel?
Filled up, never started. The best case there is. At a forecourt, and genuinely only there, that petrol is still confined to that tank — since anywhere else your car was driven to reach it. The job is draining and purging on the spot.
Started for a moment, or only your ignition on. Once primed, the fuel system has drawn petrol out of your tank up to the filter and the fuel lines. That's usually still an easy job — a drain, a flush, and the fuel filter dealt with.
Those few miles driven meant your pump running on fuel weakened by petrol the whole way. The work is your tank, your lines, your filter and clean fuel through the whole circuit, and how hard the vehicle was driven matters as much as how far. Short trips, like the school run to the local primary school, are one matter. Very different once more: a trip to St Davids, under 15 miles away, or any distance on the M4, under 50 miles from Lower Town, where your engine kept running hard.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone uneven. What you are hearing is your engine signalling fuel that no longer acts like diesel. Whether it's the verge on Old Newport Road, a lay-by or a side road, stop there and leave it. The drain and flush still come first, and they deal with it: if a vehicle is stopped quickly, lasting damage is very rare.
Petrol in a diesel myths Lower Town motorists hear
False: topping up to full with diesel makes it fine. It doesn't. Topping up takes out nothing; it gives you a bigger tank of the same mixture. A diesel fuel system doesn't tolerate petrol by percentage in the way that guidance supposes.
"Newer diesels can handle a little petrol" — a myth, and nearer the reverse. Lubrication matters more on newer diesels, not less, because their fuel passes through more precise parts at higher pressure.
This is the one that catches people. Myth: "If it starts and drives, there's no damage done." The driver of a petrol motor fed diesel usually has no choice but to stop, because it will not run, and the damage stops with them. While the pump wears, a diesel fed petrol usually starts, ticks over and drives away as if nothing has happened. Running isn't the same as fine.
Myth: "Add some two-stroke oil and drive it home." It's an old fix for a different issue. None of what petrol weakened is put back by it — and afterwards, your tank still holds the petrol.
The next start draws petrol back round your pump from the fuel lines and the filter, where some of that sits after the engine has been run. That is why draining the tank yourself doesn't leave you sorted — a myth. And, a can of petrol filled by the kerbside is truly risky.
How it happens: petrol in a diesel
No one does it on purpose, and it's seldom carelessness. A diesel nozzle generally won't go into a petrol vehicle, yet the slimmer petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one mistake easy, and just in one direction.
The moment habit stops matching the car is the moment it takes place. Courtesy car, hire car, or a motor that is new. A household with one petrol and one diesel on the driveway. A forecourt you know, but with its pumps laid out differently. Rushing for a train at Fishguard & Goodwick and fuelling up en route. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is precisely the moment it happens. Throw in rain, a phone call or a back seat full of kids, and your hand repeats what it has always done.
Preventing petrol in a diesel next time you fill up around Lower Town
- A green handle for unleaded and black for diesel is usual in the UK — but not on every forecourt. Trust the label on the petrol pump, not the colour.
- Inspect your 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.
- A coloured fob or a sticker on your diesel's key does more than any amount of intending to remember, in a home with one of each.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the petrol pump. It sounds daft and it does the trick.
- Put the phone away. This is an easy mistake to make whilst you are thinking about something else.
- Some diesels come with a filler designed to reject a petrol nozzle, and devices you can add exist for cars without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the petrol pump.
- Less petrol means a thinner mix, so stop the moment you notice — though remembering that your next step is unchanged. It is still not to start the vehicle.
Already put petrol in a diesel in Lower Town?
In that case, there's just a short order of things. Starting it is out, and so is turning on your ignition. Yet at the forecourt, at the nearest petrol station or anywhere else? Ask the attendants to help you push it away from the pump. Next, 0333 366 0103. We'll ask what went 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 — Lower Town has a page all for it.
What makes one Lower Town petrol in a diesel job cost more than the next
There's no fair single quote for this, because the four situations above are four separate tasks. Which of them you are in is chiefly what moves the cost. Where your car is matters too, and whether a technician can safely get to it, after the share of petrol to what that tank takes.
Before any quote, not after, we ask three questions: your fuel that went in, its amount, and whether it has run. That is why. Those answers are what turn a range into one firm number.
About Lower Town and its setting
Lower Town is a small suburban area situated on the coast of Pembrokeshire, with a low elevation of around 6 metres above sea level. Lower Town lies near the larger town of Fishguard and the village of Goodwick, and is within a short drive of the historic city of St Davids. Lower Town is characterised by its predominantly semi-detached housing stock, reflecting the area's development as a residential community. Lower Town is also close to the small village of Penyraber, and is around 210 miles west of London.
Lower Town and Pembrokeshire: where our fuel drain cover reaches
Lower Town rests in the SA postcode area, and the teams that answer petrol in diesel jobs there work the locations around it as well — Fishguard, Penyraber and Goodwick among them. Our technicians drain wherever the vehicle is — your own drive, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
At the petrol pump in Lower Town, right now?
Nothing beats it: that's where you now are. Keep the vehicle switched off, and ring.