Kingsdown: Petrol in a Diesel Car? How Worried to Be
Far less than you likely are, if it hasn't been started. Everyone around Kingsdown starts with "have I ruined it?", and the fair answer is usually no: petrol resting inside your tank of a diesel remains harmless till priming, cranking or driving pulls it into the system. Keep it like that: leave your engine off then ring Petrol in Diesel. Read on for three things: the effect petrol has inside a diesel engine, the clues of how far it has got, and the way to make sure you never repeat it.
Inside the motor: what petrol in a diesel does
On its way through a motor, diesel has two tasks. Before it combusts, it lubricates — then it ignites. Designed to very fine tolerances, your injectors and your pump depend on the diesel flowing through them to keep their surfaces from wearing against one another.
Petrol handles the first task poorly and the second not at all. A pump running on a petrol mix is wearing itself out, because petrol is runnier than diesel and takes away the lubrication your fuel system relies on. Petrol is also made to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that is where the knocking starts.
The shape of the trouble is plain once you put those together. The damage is done by movement, not by contact. Petrol in the tank is a fuel fault. Whatever a worn pump sheds goes on, carried by your fuel, into your injectors further along, which is why a pump that has been working on the petrol is where a mechanical fault begins.
Kingsdown, petrol in a diesel: four cases, from mild to major
Filled up, and not started: nothing beats it. At a forecourt, and really only there, the petrol is still confined to the tank — since anywhere else the car was driven to reach it. The task is draining and cleaning on the spot.
A moment's running, or merely the ignition on. With your system primed, your lines and filter now hold petrol that has come from that tank. Still generally simple: drain, flush, and your filter dealt with.
A couple of miles driven, and the pump has spent every one of them labouring on thinned fuel. Mileage is only half of it; how hard it was driven matters just as much. Either way the work includes your tank, your lines, the filter and clean fuel through the whole circuit. A school run to Cotham Gardens Primary School is one thing. A run as far as Bristol, under a mile away, is a very different job. So is any mileage on the M32, under a mile from Kingsdown, where the motor has been labouring hard throughout.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone lumpy. The engine is telling you the fuel is no longer behaving like diesel. Stop where you are — on the verge on Montague Place, at the kerb, down a side road — and don't move it. What comes first is still the fuel drain and flush, and that takes care of it, with lasting damage very uncommon when a vehicle is stopped quickly.
Petrol in a diesel stories Kingsdown people hear
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. A fuller tank of the same mix is all you get, since topping up takes out nothing. The idea behind the guidance — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the reverse. At higher pressure, through smaller components: that is how a modern diesel handles its fuel, so the lubrication matters for more, not less.
This is the one that catches drivers. Myth: "If it starts and drives, there's no harm done." The driver of a petrol motor fed diesel normally has no choice but to stop, since it will not run, and the harm stops there. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile the pump grinds. Running isn't the same as fine.
An old workaround for a different problem is behind this one. Myth: "Add some two-stroke oil and drive it home." It does not put back what petrol has weakened, and the petrol is still inside that tank after that.
Once the motor has been run, part of the petrol sits in the fuel filter and your lines, not your tank — and your next start sends it straight back through your pump. So the myth "drain the tank yourself and you're sorted" doesn't stand up. Draining petrol into a can at the roadside is also really hazardous.
How petrol ends up: petrol in a diesel
Nobody does it on purpose, and it is seldom carelessness. One way only, because of the nozzles: the smaller petrol one slips inside a diesel filler with almost no resistance, whereas the diesel one mostly will not fit a petrol motor. That is how the forecourt makes it easy.
When routine and the vehicle stop matching, it happens. Hire cars, courtesy cars, and cars that are new to you. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a well-known forecourt. Rushing for a train outside Redland and fuelling up en route. A new-to-you diesel Skoda Octavia, its first fuelling, and a driver accustomed to petrol: precisely when it occurs. Your hand repeats what it has always done once you add rain, a phone call or a back seat full of kids.
Next time you fill up in Kingsdown: avoiding petrol in a diesel
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most generally do. Check the petrol pump's label; the colour is just a hint.
- Many cars state the fuel inside the filler flap or on the cap, and so check there on your first fill in a vehicle you do not know.
- One of each in the house? Label the key to your diesel — a coloured fob, a sticker — since intending to remember is not enough.
- "Diesel", out loud, before you pick up the nozzle — every time a new or hired car needs its first tank. It sounds silly. It works.
- Mistakes like this are easy to make whilst your mind is on something else, and so the phone goes away.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler designed to refuse a petrol nozzle, and add-on devices exist for motors without one. They are a backstop, not a reason to stop reading the petrol pump.
- Stop as soon as you notice. Less petrol inside that tank means a thinner mix. It doesn't change what to do next, which is still not to start the car.
Kingsdown: already put petrol in a diesel?
The order of things is brief, then. Leave it unstarted, with the ignition switched off as well. If you are still on the forecourt — Esso or anywhere else — ask the staff to help you push the car clear of the petrol pump. Call 0333 366 0103 next, with three answers — your fuel, the approximate amount, and if it's run.
Corrosion and deposits form the trouble with AdBlue, where petrol means lost protection. So if it was AdBlue, say so — and see its own Kingsdown page.
Why one petrol in a diesel task in Kingsdown costs more than another
There's no honest single price for this, because the four scenarios above are four separate tasks. Which of them you are in is mostly what shifts the cost. Where the vehicle is matters too, and whether a van can safely reach it, after the proportion of petrol to what that tank takes.
Three questions come first, before any quote, rather than after — what was put in, how much, has it run — and this is the reason. With the answers, you get a straight figure rather than a range.
About Kingsdown and where it is
Kingsdown is a suburban area located just north of Bristol city centre, at an elevation of around 72 metres. Kingsdown sits in a densely populated part of the city, with nearby areas including Cotham and Tyndalls Park. Kingsdown is characterized by its predominantly flat-based housing stock, reflecting its urban setting. Kingsdown is close to the amenities and services of Bristol, being only 0.6 miles from the city centre.
Fuel drain cover across Bristol, Kingsdown included
Kingsdown sits in the BS postcode area, and the teams that answer petrol in diesel call-outs there work the locations near it as well — Cotham, Tyndalls Park and Bristol among them. The vehicle does not need to come to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Still at the pump around Kingsdown?
Then, you could not be in a better position. Ring, and keep it switched off.