Johnstown: Petrol in a Diesel Car? How Worried to Be
Not started? Then less worried than you likely are. Everyone around Johnstown starts with "have I wrecked it?", and the fair answer is generally no: petrol resting in your tank of any diesel stays harmless until priming, cranking or driving pulls it into the system. Keep it that way: leave the motor off then phone Petrol in Diesel. What petrol actually does to a diesel, how to judge how far it has travelled, and how to keep it from happening a second time: that is the remainder of this page.
Inside the motor: what petrol in a diesel does
Diesel has two jobs on its way through a motor. Oiling comes before burning; it does both. What keeps the surfaces inside the high-pressure fuel pump and your injectors from wearing down against one another is the diesel passing through them — they're made to extremely fine gaps.
Petrol handles the first job badly and the second not at all. Being less viscous than diesel, petrol strips away the protection a fuel system needs, so a pump running on that mixture wearing itself. It's also made to resist igniting under compression — the opposite of what a diesel needs — which is why you hear the clattering.
Put those together and the shape of the trouble is clear. The harm is done by movement, not by contact. All a tank with petrol in it amounts to is a fuel problem. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the fuel injectors downstream.
How serious is petrol in a diesel? Four scenarios our technicians see around Johnstown
Filled but not once started — the best it gets. On a forecourt, and really only there, the petrol is still confined to the tank — because everywhere else the car was driven to get to it. The task is draining and purging on the spot.
The ignition turned on, or a short start. With the fuel system primed, the fuel lines and filter now contain petrol that has come from that tank. Still normally simple: drain, flush, and your filter sorted.
Those few miles driven meant your pump labouring on fuel diluted by petrol throughout. The work is the tank, the lines, the fuel filter and clean fuel through the whole system, and how hard your car was driven matters as much as how far. On the school run to the local primary school, the miles is short. A run as far as Swansea, under 25 miles away, is a very different job. So is any distance on the M4, under 15 miles from Johnstown, where your engine has been labouring hard the whole time.
It protested, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone lumpy. What you are hearing is your engine reporting fuel that no longer runs like diesel. Leave it where it has stopped: a lay-by, a quiet street, the verge on Old Llansteffan Road. A vehicle stopped quickly very seldom has permanent damage, as the drain and the flush, which still go first, sort it out.
What Johnstown 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." Nothing is removed by topping up — you are left with a bigger tank, still the same mixture. Percentage isn't how a diesel fuel system tolerates petrol, however much that advice supposes.
If anything, the reverse holds. Myth: "A modern diesel can cope with a bit of petrol." A modern diesel runs its fuel through smaller parts at higher pressure, which makes the lubrication matter more, not less.
This is the one that fools people. Myth: "If it starts and drives, there is no damage done." Feed diesel to a petrol engine and it usually won't run, and so the motorist stops — and the damage stops with them. While your pump grinds, a diesel fed petrol normally starts, idles and drives away as if nothing has happened. Running is not the same as fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a distinct issue. What petrol has thinned stays diluted, and the petrol remains in that tank regardless.
Myth: "Drain that tank yourself and you're sorted." Once your engine has run, some of that petrol is no longer inside the tank: it is in the filter and the fuel lines, and it goes right back through your pump on your next start. It's also truly dangerous to drain petrol into a can at the roadside.
Petrol in a diesel: how does it happen?
Nobody does it on purpose, and it is seldom carelessness. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slips into a diesel filler with almost no resistance, whilst a diesel nozzle mostly won't go into a petrol vehicle at all. So the slip runs one way.
It happens when routine and the vehicle stop matching. A vehicle that's new to you — hired, on loan as a courtesy car, or brand new. Households running one of each, petrol and diesel. Your normal forecourt, its pumps suddenly in a different order. A rushed fill en route to Carmarthen with a train to catch. A new-to-you diesel Renault Megane, its first fuelling, and a driver used to petrol: precisely when it takes place. The hand does what it has always done when you add rain, a phone call or a back seat full of kids.
Avoiding petrol in a diesel next time you fill up around Johnstown
- 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 just a hint.
- Inspect the filler flap. Many vehicles state the fuel inside the flap or on the cap. Look at it on the first fill in any motor you do not know.
- One of each in the house? Mark the key to the diesel — a coloured fob, a sticker — since meaning to remember is not enough.
- "Diesel", aloud, before you pick up the nozzle — each time a new or hired car needs its first tank. It seems daft. It does the trick.
- Tuck your phone away. This is an easy mistake to make whilst you are thinking about something else.
- Add-on devices are available for vehicles without one, and some diesels come with a filler that will not take a petrol nozzle. Useful — but a backstop only, never a reason to stop checking the label.
- Less petrol makes a thinner mixture, and so stop the moment you notice — while remembering that the next stage is unchanged. It's still not to crank it.
Johnstown: already put petrol in a diesel?
Then the order of things is short. Leave it unstarted, with the ignition switched off as well. Yet on the forecourt, at Johnstown Filling Station or anywhere else? Ask the attendants to help you roll it clear of the pump. Then ring 0333 366 0103 and tell us what went in, about how much, and if it's run.
Say so if it was AdBlue rather than petrol: it's a different issue, with its own page for Johnstown, because AdBlue brings corrosion and deposits rather than lost protection.
Why one petrol in a diesel job around Johnstown costs more than another
Four different jobs lie behind the four scenarios above — which is why there is no fair single price. What moves the cost is mostly which of them you're in. Beyond that it's the share — how much petrol got in against how much the tank holds — and then where the vehicle is and whether a technician can reach it safely.
Three queries come first, before any quote, instead of after — what got in, how much, has it run — and that is the reason. Given those replies, you get a straight figure rather than a range.
About Johnstown, for a moment
Johnstown is a suburban area in Carmarthenshire, situated on the riverside at a low elevation of around 12 metres. Johnstown lies near several small communities, including Pibwrlwyd, Pen-sarn, and Llanllwch, and is within commuting distance of Swansea, which is approximately 23 miles away. Johnstown has a population of around 1505 people and is characterised by predominantly detached housing.
Johnstown and Carmarthenshire: where our fuel drain cover reaches
The vans answering petrol in diesel calls in Johnstown, in the SA postcode area, also work the spots near it, Pibwrlwyd, Pen-sarn and Llanllwch included. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations we work, and your vehicle does not need to move to us.
In Johnstown and still at the pump?
No position is better: that is where you are. Turned off it remains; then phone.