Miskin: Petrol in a Diesel Car? How Worried to Be
Not started? Then less worried than you probably feel. Everyone around Miskin begins with "have I ruined it?", and the honest answer is normally no: petrol left inside the tank of any diesel stays harmless until priming, cranking or driving pulls it into the fuel system. Petrol in Diesel is who to ring, with the engine left off, so it stays that way. Further down, this page sets out what petrol really does inside a diesel, how far it might have got, and how to stop it happening to you a second time.
The motor and petrol in a diesel: what goes on
On its way through an engine, diesel has two tasks. It protects to begin with, and only then does it burn. Designed to extremely fine tolerances, the injectors and your pump depend on your diesel flowing through them to stop their surfaces wearing against one another.
Of these two jobs, petrol manages the first badly and the second not at all. A pump running on a petrol blend is wearing itself out, because petrol is thinner than diesel and takes away the lubrication the fuel system relies on. Petrol is also made to resist igniting under compression — the reverse of what a diesel needs from its fuel — and that's where the knocking comes.
Taken together, they show the shape the problem has. Not contact but circulation is what does the harm. Where that petrol is only inside your tank, it is a problem of fuel, nothing more. The start of a mechanical one is a pump that has been labouring on that petrol — and whatever a worn pump sheds moves on with your fuel to the injectors beyond it.
Four situations our engineers see in Miskin: how serious is petrol in a diesel?
Fuelled up, never started. The best case there can be. On a forecourt, and genuinely only there, that petrol is still confined to the tank — since everywhere else the vehicle was driven to get to it. The task is draining and flushing on the spot.
Ignition on, or started for a moment. With the system primed, the fuel lines and filter already contain petrol that has come from your tank. Normally nothing more than clearing, rinsing and sorting the filter, and so still straightforward.
Some miles driven, and the pump has spent every one of them labouring on weakened fuel. The work is that tank, the fuel lines, the fuel filter and clean fuel through the whole system, and how hard the vehicle was driven matters as much as how far. The school run to the local primary school is one matter. A run as far as Cardiff, under 10 miles away, is a very different task. So is any distance on the M4, under a mile from Miskin, where the motor has been running hard throughout.
It protested, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone ragged. The fuel is not behaving like diesel any more, and your motor is saying so. Pull up wherever you are — the verge on New Mill Corner, a lay-by, a side street — and leave it where it is. What comes first is still the drain and flush-through, and that deals with it, with long-term damage very uncommon when a car is pulled over early.
What Miskin drivers get told about petrol in a diesel — and the myths in it
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. Nothing is removed when you top up — that tank just holds more of the same blend. A diesel fuel system doesn't tolerate petrol by percentage in the way that advice supposes.
Myth: "A current diesel can cope with a bit of petrol." If anything, the reverse. A modern diesel sends its fuel through smaller parts at higher pressure, which makes the protection matter more, not less.
Myth: "If it starts and drives, there is no harm done." This is the one that catches motorists. The driver of a petrol engine fed diesel normally has no choice but to stop, because it will not run, and the damage stops there. A diesel fed petrol usually starts, idles and drives away as if nothing has happened, while the pump grinds. Running isn't the same as fine.
An old fix for a different problem is behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol diluted is put back by it — and later, your tank still contains that petrol.
Once the motor has been run, part of that petrol is in your filter and your lines, not the tank — and the next start sends it straight back through your pump. So the myth "drain the tank yourself and you're sorted" doesn't hold. And, a can of petrol filled by the roadside is genuinely dangerous.
How does petrol in a diesel happen?
A careless moment is rarely the cause, and nobody means to do it. 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 mostly will not go into a petrol vehicle at all. So the slip runs one way.
When routine and the car stop matching, it happens. A new motor, a hire car or a courtesy car. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a familiar forecourt. A rushed fill en route to Pontyclun with a train to catch. Years of petrol motors behind you, a diesel Renault Clio in front of you on the forecourt for its first tank — that is when. Throw in a back seat full of children, a phone call or rain, and habit takes over.
Avoiding petrol in a diesel next time you fill up in Miskin
- Not every forecourt in the UK follows green for unleaded and black for diesel, even if most generally do. Check the petrol pump's label; the colour is just a hint.
- The first fill in a strange vehicle is the time to check the filler flap — inside it, or on the cap, many vehicles state which fuel to use.
- Good intentions count for less than a sticker or a fob in a bright colour on your diesel's key if a house has one of each. So mark it.
- Before the nozzle leaves the petrol pump the first time you fuel a hired or new vehicle, say "diesel" aloud. Silly, yes, yet it works.
- Whilst you are thinking about something else, this is an easy mistake to make — so tuck the phone away.
- Add-on devices are available for vehicles without one, and some diesels are built with a filler that won't take a petrol nozzle. Useful — but a safety net only, never a reason to stop checking the label.
- Spotting it mid-fill? Stop at once. A weaker mix follows from less petrol inside the tank, but your next stage stays the same: don't fire it up.
Already put petrol in a diesel in Miskin?
Then the order of things is short. Leave it unstarted, with your ignition switched off too. If you are still on the forecourt — Texaco or anywhere else — ask the staff to help you push the vehicle clear of the pump. What got in, roughly how much, and whether it's run: tell us those when you ring 0333 366 0103.
Corrosion and deposits form the trouble with AdBlue, where petrol means lost protection. So if it was AdBlue, say so — and see its own Miskin page.
One petrol in a diesel task in Miskin costs more than another. Why?
A fair single quote doesn't exist here: four situations, four separate jobs. Which of them you're in is chiefly what moves the cost. The proportion counts next, meaning how much of your tank is petrol, followed by the position of the car and whether reaching it is safe for a van.
Three queries come first, before any quote, rather than after — what got in, how much, has it run — and this is the reason. Their replies are what change a range into one firm number.
About Miskin and where it is
Miskin is a village situated on the banks of the River Ely in Rhondda Cynon Taf, with a mix of rural and suburban characteristics. Miskin has a relatively low elevation of 47 metres above sea level and is located near several other small villages, including Mwyndy and Pontyclun. Miskin is also close to the city of Cardiff, which is approximately 9 miles away. Miskin is predominantly composed of detached housing, reflecting its suburban edge character.
Fuel drain cover in Miskin and across Rhondda Cynon Taf
Miskin waits in the CF postcode area, and the vans that answer petrol in diesel call-outs there work the places around it as well — Mwyndy, Pontyclun and Brynsadler among them. Our engineers drain wherever your car is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
Miskin: still at the pump?
The best spot there is, then — that's where you are. Ring, and leave it turned off.