How Worried Should You Be? Petrol in a Diesel Car in Cwmgwrach
Far less than you likely are, if it hasn't been started. Petrol sitting in a diesel tank does nothing to your engine till something draws it through the fuel system — the ignition priming the pump, your starter, or the drive on its own. So the truthful answer to the first question anyone around Cwmgwrach asks, "have I wrecked it?", is normally no. Keep it that way: leave your motor off and phone Petrol in Diesel. Read on for three things: the effect petrol has inside a diesel motor, the clues of how far it has spread, and the way to make sure you never do it again.
The motor and petrol in a diesel: what happens
Passing through a motor, diesel does two things at the same time. Lubricating comes before burning; it does both. Your high-pressure pump and your injectors are made to very fine clearances, and your diesel passing through them is what keeps those surfaces from wearing down against one another.
The second task petrol does not do at all, and the first it does badly. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump running on the blend wearing itself. It's equally made to resist igniting under compression — the reverse of what a diesel needs — which is why you hear the rattling.
Seen together, they show what shape the issue takes. It is movement that causes the damage, not contact. Where that petrol is only inside that tank, it's a problem of fuel, nothing more. A pump that has been working on that petrol is the start of a mechanical one, and whatever a worn pump sheds travels on with the fuel to the fuel injectors downstream.
Petrol in a diesel in Cwmgwrach: how serious is it? Four situations
Filled but never started — the best it gets. Being at a forecourt is what makes this possible: elsewhere, the vehicle has been driven there to begin with. With that petrol kept inside your tank alone, it is emptied and rinsed on the spot, and nothing more is needed.
A moment's running, or just the ignition on. The system has been bled, and so petrol has left the tank and reached the fuel filter and the fuel lines. Drain, flush, deal with the filter: still usually easy.
Those few miles on the road meant your pump working on fuel weakened by petrol throughout. Miles is only half of that; how hard it was driven counts just as much. Either way the work runs to your tank, your lines, your filter and fresh fuel through the entire circuit. Driving the children to the local primary school is one kind of trip. A run as far as Swansea, under 25 miles away, is a very different task. So is any distance on the M4, under 15 miles from Cwmgwrach, where the motor has been running hard throughout.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone uneven. The engine is telling you your fuel is no longer acting like diesel. Stop wherever you are — the verge on Heol-Wenallt, a lay-by, a side street — then leave it where it is. A vehicle stopped quickly very seldom has lasting damage, because the fuel drain and the flush-through, which still go first, sort it out.
Cwmgwrach drivers and that petrol in a diesel myths they hear
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. A bigger tank of the same mix is all it gives, because topping up removes nothing. Percentage isn't how a diesel fuel system tolerates petrol, whatever that guidance supposes.
Not so: a modern diesel copes with a bit of petrol. Rather, the opposite. Protection counts more on current diesels, not less, since their fuel runs through more precise components at higher pressure.
This is the one that catches drivers. Myth: "If it starts and drives, there's no damage done." Diesel in a petrol motor generally means a motor that won't run: the driver stops, and so does the harm. A diesel fed petrol usually starts, idles and drives away as if nothing has happened, whilst your pump grinds. 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 fault. None of what petrol thinned gets put back by it — and afterwards, your tank still contains the petrol.
Myth: "Drain your tank yourself and you are sorted." After the motor has been run, some of that petrol is no longer in your tank: it's in the filter and your lines, and it goes right back through your pump at your next start. It is also genuinely risky to drain petrol into a can by the kerbside.
Petrol in a diesel: how does it happen?
Carelessness is rarely the cause, and no one means to do it. A diesel nozzle mostly will not fit a petrol car, but 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.
It occurs when habit and your car stop matching. Hire cars, courtesy cars, and vehicles that are new to you. One petrol and one diesel on the driveway of the same household. A forecourt you know, but with its pumps laid out differently. A hurried fill en route to Treherbert with a train to catch. The first fill-up in a diesel Renault Megane after years of driving petrol is exactly 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.
Cwmgwrach drivers: how to prevent petrol in a diesel next time
- The label is what matters, so read the petrol pump instead of the colour: in the UK unleaded handles are usually green and diesel black, but not on each forecourt.
- Plenty of cars state the fuel type inside your filler flap or on the cap, so check it on your first fill in any car you don't know.
- Good intentions do less than a sticker or a fob in a bright colour on your diesel's key when a household has one of each. So label it.
- Before the nozzle comes off the petrol pump the first time you fill a hired or new car, say "diesel" out loud. Silly, perhaps, yet it works.
- Put your phone away. This is an easy mistake to make while you're thinking about something else.
- Add-on devices exist for motors without one, and some diesels are built with a filler that will not accept a petrol nozzle. Useful — but a safety net at best, never a reason to stop checking the label.
- Stop as soon as you notice. Less petrol in your tank means a weaker mix. It doesn't change what to do next, which is still not to start the car.
Petrol already in a diesel in Cwmgwrach? Start here
The order of things is short, then. Leave it unstarted, with the ignition off too. Yet on the forecourt, at Texaco or anywhere else? Ask the attendants to help you roll the vehicle clear of the pump. Then phone 0333 366 0103 and tell us what was put in, roughly how much, and whether it has run.
If it was AdBlue instead of petrol, say so. That is a different issue — corrosion and deposits rather than lost protection — and it has its own page for Cwmgwrach.
Cwmgwrach petrol in a diesel jobs: why one costs more than another
Four separate jobs lie behind the four scenarios above — which is why there is no fair single price. Which of them you're in is mostly what shifts the cost. Where your car is counts too, and whether a van can safely reach it, after the proportion of petrol to what the tank holds.
What went in, how much, and if it's run — three queries our technicians ask before pricing, not after, for exactly that reason. With the replies, there is a straight figure instead of a range.
About Cwmgwrach
Cwmgwrach is a small village in Neath Port Talbot, situated on the riverside at an elevation of 58 metres. Cwmgwrach lies near the communities of Blaengwrach, Morfa Glas, and Pentreclwydau, and is approximately 15 miles from Swansea. Cwmgwrach has a population of around 737 people, predominantly living in semi-detached housing. Cwmgwrach is located in a scenic area, with the village surrounded by Welsh countryside.
Fuel drain cover across Neath Port Talbot, Cwmgwrach included
Cwmgwrach sits in the SA postcode area, and the vans that answer petrol in diesel calls there work the spots around it as well — Blaengwrach, Morfa Glas and Pentreclwydau among them. The car doesn't need to move to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own drive.
Cwmgwrach: still at the pump?
Then you are in the best place there is. Leave the vehicle turned off, then ring.