Dyffryn Dowlats: Petrol in a Diesel Car? How Worried to Be
Probably less than you are now — provided nobody has started the vehicle. "Have I ruined it?" is the first question anyone in Dyffryn Dowlats asks, and the truthful answer is generally no, because petrol resting in a diesel tank hurts nothing till it's drawn through the fuel system — by ignition priming, by your starter, or by being driven. Leave the engine off and call Petrol in Diesel — that is how you keep it like that. Read on for three things: the effect petrol has inside a diesel engine, the signs of how far it has spread, and the way to make sure you don't repeat it.
Your engine and petrol in a diesel: what goes on
Diesel does two tasks on its way through an engine. It combusts, and before it ignites it lubricates. What stops the surfaces inside the high-pressure pump and the fuel injectors from wearing against one another is the diesel flowing through them — they're built to very fine gaps.
Badly at the first, not at all at the second: that's petrol. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, so a pump on that mixture wearing itself. It's equally made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the clattering.
The shape of the trouble is plain when you put those together. The damage is done by circulation, not by contact. All a tank with petrol in it amounts to is a fuel fault. Whatever a worn pump sheds goes on, carried by your fuel, into your injectors downstream, which is why a pump that has worked on that petrol is where a mechanical fault starts.
Four situations our technicians see in Dyffryn Dowlats: how bad is petrol in a diesel?
Filled but never started — as good as it gets. On a forecourt, and really only there, the petrol is still limited to your tank — because everywhere else the vehicle was driven to get to it. The job is emptying and rinsing on the spot.
The ignition turned on, or a brief start. With the system primed, the lines and filter already contain petrol that has come from your tank. That's normally still a straightforward job — a drain, a flush, and the fuel filter dealt with.
Those few miles driven meant the pump running on fuel weakened by petrol the whole way. Tank, lines, filter, then clean fuel run through the entire system: that is this work, and the way your car was driven counts as much as the miles. A school run to the local primary school is one thing. Very different again: a run to Cardiff, under 10 miles away, or any mileage on the M4, under 5 miles from Dyffryn Dowlats, where the engine never stopped working hard.
It complained, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone lumpy. The motor is telling you the fuel is no longer acting like diesel. Whether it's the verge on Coed y Broch, a lay-by or a side road, stop there and leave it. The drain and flush still go first, and they deal with it: when a car is pulled over soon, long-term damage is very rare.
Dyffryn Dowlats drivers and the petrol in a diesel stories they hear
Myth: topping up to full with diesel makes it fine. It doesn't. Nothing is removed when you top up — your tank just holds more of the same blend. That advice assumes a diesel fuel system handles petrol by percentage. It does not.
"Current diesels can handle a little petrol" — a myth, and closer to the reverse. Smaller components and higher pressure are how a newer diesel runs its fuel, and that makes the lubrication matter more, not less.
One myth that catches motorists off guard: if it starts and drives, it must be unharmed. The motorist of a petrol engine fed diesel usually stops, since it will not run, and the harm stops there. While the pump grinds, a diesel fed petrol normally starts, ticks over and drives away as if nothing has happened. Running does not mean fine.
An old fix for a separate problem lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol thinned gets put back by it — and afterwards, your tank still contains that petrol.
The next start sends petrol back round your pump from the fuel lines and your filter, where some of that ends up once the motor has run. That's why draining the tank yourself does not sort it — a myth. Clearing petrol into a can by the roadside is also genuinely risky.
Petrol in a diesel: how does it occur?
A careless moment is rarely the cause, and no one means to do it. One way only, since of the nozzles: the smaller petrol one slips inside a diesel filler with almost no resistance, while the diesel one mostly won't fit a petrol car. That is how the forecourt makes it easy.
It happens when habit and the car stop matching. A new vehicle, a hire car or a courtesy car. A household with one petrol and one diesel on the driveway. A forecourt you know, but with its pumps arranged differently. A rushed fill on the way to Trefforest Estate with a train to catch. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is precisely the moment it occurs. Add a back seat full of children, a phone call or rain, and the hand takes over.
Next time you fill up in Dyffryn Dowlats: preventing petrol in a diesel
- The label is what matters, so read the pump rather than the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt.
- In a motor you don't know, look inside the flap over the filler or at the cap before your first fill: many cars state the fuel type there.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of intending to remember, in a house with one of each.
- Before the nozzle comes off the pump the first time you fill a hired or new vehicle, say "diesel" out loud. Daft, yes, but it works.
- Mistakes like this are simple to make while 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 built to refuse a petrol nozzle, and add-on devices are available for vehicles without one. They are a backstop, not a reason to stop checking the pump.
- Less petrol means a weaker mixture, so stop as soon as you notice — while remembering that your next step is unchanged. It is still not to crank it.
Dyffryn Dowlats: already put petrol in a diesel?
Short and simple, then, is the order of things. Don't start the car, and do not turn your ignition on. The attendants at the forecourt — whether at Texaco itself or wherever you filled up — will usually help roll it away from the petrol pump if you ask. Ring 0333 366 0103 next, with three facts — your fuel, the approximate quantity, and if it has run.
If it was AdBlue instead of petrol, say so. That's a separate issue — corrosion and deposits rather than lost protection — and it has its own page for Dyffryn Dowlats.
Dyffryn Dowlats petrol in a diesel tasks: why one costs more than another
There's no honest single price for this, since the four situations above are four different tasks. What shifts the cost is mostly which of them you're in. The ratio matters next, meaning how much of the tank is petrol, followed by the position of the car and whether getting to it is safe for a van.
Three questions come first, before quoting, instead of after — what got in, how much, has it run — and this is the reason. Given the replies, there is a straight figure instead of a range.
About Dyffryn Dowlats and where it is
Dyffryn Dowlats is a suburban area in Rhondda Cynon Taf, situated near the River Taff and close to the nearby communities of Church Village and Ton-Teg. Dyffryn Dowlats has a mix of housing types, but is predominantly characterised by detached homes. Dyffryn Dowlats is located near Cardiff, the capital city of Wales, and is within commuting distance of the city centre. Dyffryn Dowlats sits at an elevation of around 86 metres above sea level, in a riverside setting that offers scenic views of the surrounding countryside.
Fuel drain cover across Rhondda Cynon Taf, Dyffryn Dowlats included
Church Village, Ton-Teg and Upper Church Village are among the places around Dyffryn Dowlats that the same teams work, answering petrol in diesel calls across Dyffryn Dowlats's CF postcode area. We drain where the vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
Still at the petrol pump around Dyffryn Dowlats?
The best spot there is, then — that is where you are. Keep it off. Call.