How Worried Should You Be? Petrol in a Diesel Car in Caer-went
Likely less than you already are — as long as nobody has started it. "Have I ruined it?" is the first thing everyone around Caer-went asks, and the honest answer is usually no, since petrol resting in a diesel tank harms nothing till it's dragged through the system — by ignition priming, by the starter, or by driving. Petrol in Diesel is who to ring, with the engine kept off, and so it stays that way. The remainder of this page covers what petrol actually does to a diesel, how to tell how far it has got, and how to make sure it doesn't happen to you again.
Petrol in a diesel: what does it do to your engine?
Passing through an engine, diesel does two jobs at once. It lubricates to begin with, and after that does it burn. Made to extremely fine tolerances, your injectors and your pump depend on your diesel moving through them to stop their surfaces wearing against one another.
The second task petrol doesn't do at all, and the first it does poorly. It is thinner than diesel and takes away the protection your fuel system hinges on, so a pump running on a petrol mix is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That's where the clattering comes from.
Seen together, they show the shape the problem has. The damage is done by circulation, not by contact. Where that petrol is only inside your tank, it's a fault of fuel, nothing more. After your pump has been running on that petrol, a mechanical fault has begun: anything shed by a pump that's wearing down travels onward to your injectors with your fuel.
How serious is petrol in a diesel? Four scenarios our technicians see around Caer-went
The best case there can be: filled up, never started. Being on a forecourt is what makes this the case: elsewhere, your car has been driven there to begin with. With that petrol kept inside the tank alone, it is emptied and flushed right where it stands, and nothing more is needed.
The ignition turned on, or a short start. Petrol has come out of your tank and got to the fuel filter and your lines, because the system has been bled. That is usually still a straightforward task — a drain, a flush, and the filter seen to.
A few miles driven, and the pump has spent every one of them labouring on weakened fuel. Tank, lines, filter, then clean fuel run through the entire system: that is the work, and the way the vehicle was driven counts as much as the miles. A school run to Lift Offa's Mead is one matter. Very different once more: a run to Newport, under 15 miles away, or any miles on the M48, under a mile from Caer-went, where the engine kept running hard.
Driven till it protested. Knocking, an uneven idle, smoke, a throttle that has gone soft. The fuel is not behaving like diesel any more, and your engine is saying so. Stop on the spot — on the verge on School Lane, at the kerb, down a side road — and don't move it again. A car stopped quickly very seldom has lasting damage, because the fuel drain and the flush-through, which still go first, take care of it.
What Caer-went people get told about petrol in a diesel — and the myths in it
False: topping up to full with diesel makes it fine. It does not. A bigger tank of the same mixture is all you get, since topping up removes nothing. Percentage is not how a diesel fuel system copes with petrol, however much that advice assumes.
If anything, the reverse holds. Myth: "A newer diesel can cope with a bit of petrol." A modern diesel runs its fuel through finer components at higher pressure, which makes the protection matter more, not less.
The myth that catches people off guard: if it starts and drives, it must be unharmed. The driver of a petrol engine fed diesel normally has no choice but to stop, since it will not run, and the harm stops with them. Whilst your pump wears, a diesel fed petrol normally starts, ticks over and drives away as though nothing has happened. Fine and running are not the same thing.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a distinct issue. That petrol is still inside that tank afterwards, and whatever it has diluted is not put back.
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 that tank yourself and you are sorted" does not hold. It's also really risky to drain petrol into a can at the kerbside.
Petrol in a diesel: how does it happen?
A careless moment is seldom the cause, and no one means to do it. One way only, since of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, whereas the diesel one generally will not fit a petrol motor. That is how the forecourt makes it straightforward.
Routine and your car getting out of step is how it takes place. A vehicle that's new to you — a hire car, on loan as a courtesy car, or brand new. Households running one of each, petrol and diesel. The pumps in a different order on a familiar forecourt. Rushing for a train at Caldicot and filling up en route. Precisely the moment it happens: after years of driving petrol, someone fills a diesel Renault Clio for the first time. Add a back seat full of kids, a phone call or rain, and the hand takes over.
Caer-went motorists: how to prevent petrol in a diesel next time
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most usually do. Read the petrol pump's label; the colour is only a hint.
- In a car you do not know, look inside the flap over the filler or at the cap before your first fill: plenty of cars print the fuel type there.
- One of each in the household? Mark your key to the diesel — a coloured fob, a sticker — because meaning to remember isn't enough.
- "Diesel", aloud, before you pick up the nozzle — every time a new or hired car needs its first tank. It seems silly. It does the trick.
- Thinking about something else is when this becomes an easy mistake to make, so put your phone away and keep your mind on the pump.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler designed to block a petrol nozzle, and add-on devices exist for motors without one. They are a safety net, not a reason to stop checking the pump.
- Spotting it halfway? Stop there and then. A weaker blend follows from less petrol inside your tank, yet your next step remains the same: don't crank it.
Caer-went: already put petrol in a diesel?
The order of things is short, then. Don't switch the ignition on, and don't fire it up. Ask the staff to help you roll it clear of the pump if you're still at the forecourt, whether that's BP or anywhere else. Ring 0333 366 0103 next, with three facts — your fuel, the approximate amount, and whether it's run.
Corrosion and deposits are the trouble with AdBlue, whereas petrol means lost lubrication. So if it was AdBlue, say so — and see its own Caer-went page.
What makes one Caer-went petrol in a diesel task cost more than the next
There is no honest single quote for this, because the four scenarios above are four separate tasks. Chiefly, the cost moves with which one you're in. Where the vehicle is matters too, and whether a technician can safely reach it, after the proportion of petrol to what the tank takes.
Before any quote, not after, come three queries: the fuel that was put in, the quantity, and whether it has run. That is why. Those replies are what turn a range into one firm number.
About Caer-went
Caer-went is a coastal village in Monmouthshire, situated near the mouth of the Caerwent Brook and close to the city of Newport. Caer-went has a population of around 1114 people and is characterised by detached housing. Caer-went sits at a low elevation of approximately 30 metres above sea level, looking out towards the Bristol Channel. Caer-went is located near several notable landmarks, including Brockwells and Highmoor Hill.
Across Monmouthshire and in Caer-went: fuel drain cover
Caerwent Brook, Brockwells and Highmoor Hill are among the locations near Caer-went that the same teams work, answering petrol in diesel calls across Caer-went's NP postcode area. You need not bring your car to us. Forecourts, supermarket car parks, lay-bys and your own drive are all places we drain.
At the pump in Caer-went, still?
In that case, you could not be in a better place. Keep it switched off, and ring.