How Worried Should You Be? Petrol in a Diesel Car in Undy
Probably less than you are now — as long as nobody has started the car. Until your ignition primes the pump, your starter turns, or your vehicle is driven, petrol in a diesel tank just waits there and does nothing. Which makes the honest reply to the first Undy query — "have I ruined it?" — normally no. Petrol in Diesel is who to call, with the motor left off, and so it remains that way. What petrol actually does to a diesel, how to judge how far it's travelled, and how to stop it from happening again: that is the remainder of this page.
The motor and petrol in a diesel: what goes on
Two tasks fall to diesel on its journey through a motor. It lubricates first, and after that does it burn. Built to very fine gaps, the fuel injectors and the pump depend on the diesel moving through them to keep their surfaces from wearing against one another.
Of these two tasks, petrol manages the first poorly and the second not at all. A pump running on a petrol mixture is wearing itself out, since petrol is thinner than diesel and takes away the lubrication the fuel system relies on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that's where any knocking starts.
Put those together and the shape of the issue is clear. The damage is done by circulation, not by contact. Petrol in the tank is a fuel problem. After your pump has been working on that petrol, a mechanical issue has begun: whatever is shed by a pump that's grinding is carried downstream to your injectors with the fuel.
Four situations we see in Undy: how serious is petrol in a diesel?
Fuelled up, not once started. The best case there can be. Being on a forecourt is what makes this possible: elsewhere, the vehicle has been driven there to begin with. With the petrol kept in your tank alone, it is drained and flushed right where it stands, and nothing more is needed.
Ignition on, or started for a second. Once primed, the system has drawn petrol from your tank as far as the fuel filter and your lines. Drain, flush, deal with your filter: still normally simple.
Your pump has spent a couple of miles on diluted fuel — that is what driving the vehicle meant. How hard the car was driven counts as much as how far, and this work covers that tank, your lines, your filter and clean fuel through the whole system. A school run to the local primary school is one thing. A run as far as Newport, under 10 miles away, is a very different task. So is any mileage on the M4, under a mile from Undy, where your engine has been working hard throughout.
It protested, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone lumpy. The motor is telling you your fuel is no longer acting like diesel. Pull up where you are — on the verge on Main Road, at the kerb, down a side road — and don't move it again. What comes first is still the fuel drain and flush, and that takes care of it, with lasting damage very rare when a vehicle is pulled over soon.
What Undy motorists get told about petrol in a diesel — and the stories in it
Myth: topping up to full with diesel makes it fine. It doesn't. Topping up removes nothing; it gives you a fuller tank of the same mix. A diesel fuel system doesn't accept petrol by percentage in the way that advice assumes.
Not so: a current diesel copes with a bit of petrol. Rather, the reverse. At higher pressure, through finer components: that is how a current diesel moves its fuel, and so the lubrication matters more, not less.
"It starts, it drives, and so no harm done" — the myth that trips up more drivers than any other. Diesel in a petrol motor normally leaves a motor that will not run: the driver stops, and so does the harm. While the pump grinds, a diesel fed petrol normally starts, ticks over 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, borrowed from a fix from years ago, for a distinct issue. The petrol is still in your tank afterwards, and whatever it has thinned isn't put back.
"Drain it yourself and you're sorted" — a myth, because after it's been running some petrol sits in your filter and lines, ready to go right back through the pump at your next start. Also, a can of petrol filled at the roadside is truly hazardous.
Petrol in a diesel: how does it happen?
Carelessness is rarely the cause, and no one means to do it. The petrol nozzle is the narrower of the two and slips into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol motor at all. The forecourt makes it simple, and the mistake runs one way.
Habit and your car falling out of step is how it occurs. Hire cars, courtesy cars, and cars that are new to you. Households running one of each, petrol and diesel. The pumps in a different order on a well-known forecourt. A rushed fill en route to Severn Tunnel Junction with a train to catch. A new-to-you diesel Volkswagen Passat, its first fuelling, and a motorist used to petrol: precisely when it occurs. With rain, a call coming in, or children to deal with, the hand simply does what it has always done.
How to prevent petrol in a diesel at your next fill-up in Undy
- The label is what counts, and so check the pump instead of the colour: in the UK unleaded handles are normally green and diesel black, yet not on each forecourt.
- Many motors state the fuel type inside the filler flap or on the cap, and so check there on the first fill in any vehicle you do not know.
- One of each in the household? Label your key to your diesel — a bright fob, a sticker — since meaning to remember isn't enough.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump. It seems daft and it does the trick.
- Put the phone away. This is an easy mistake to make while you're thinking about something else.
- Some diesels come with a filler built to reject a petrol nozzle, and devices you can add exist for motors without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the pump.
- The moment you realise, stop: less petrol inside the tank makes a weaker mixture. What to do next doesn't change, though — still do not fire it up.
Already put petrol in a diesel in Undy?
Short and simple, then, is the order of things. Don't fire it up, and do not turn the ignition on. The attendants on the forecourt — whether at BP itself or wherever you filled up — will usually help push it away from the pump if you ask. Next, 0333 366 0103. We'll ask what was put in, roughly how much, and if it's been run.
If it was AdBlue instead of petrol, say so. That is a different issue — corrosion and deposits and not lost lubrication — and it has its own page for Undy.
One petrol in a diesel task around Undy costs more than another. Why?
There is no honest single quote for this, since the four scenarios above are four different tasks. The situation itself does most of the work of moving the cost. Where the car is matters too, and whether a van can safely get to it, after the proportion of petrol to what the tank holds.
Ahead of any quote, not after, we ask three queries: the fuel that went in, its amount, and whether it's run. That's why. Their replies are what change a range into one firm number.
About Undy, briefly
Undy is a coastal village in Monmouthshire, situated near the mouth of the Severn Estuary at an elevation of around 12 metres. Undy lies close to the cities of Newport and Cardiff, and is surrounded by nearby places such as Vinegar Hill and Whitewall Common. Undy has a population of approximately 1996 people, living in predominantly detached housing. Undy is located about 7.7 miles from Newport and 115.7 miles from London.
Fuel drain cover across Monmouthshire, Undy included
The teams answering petrol in diesel jobs around Undy, in the NP postcode area, equally work the locations near it, Vinegar Hill, Whitewall Common and Magor among them. A forecourt, a supermarket car park, a lay-by or your own drive are all spots we work, and your vehicle doesn't need to come to us.
In Undy and still at the petrol pump?
The best position there is, then — that's where you are. Switched off it stays; then ring.