Culnady: Petrol in a Diesel Car? How Worried to Be
Less than you likely are, provided it hasn't been started. Till your ignition primes the pump, the starter turns, or your car is driven, petrol in a diesel tank simply waits there and does no harm. Which means the honest reply to the first Culnady question — "have I ruined it?" — normally no. To leave the car like that, ring Petrol in Diesel then leave the motor alone. The rest of this page covers what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
Your engine and petrol in a diesel: what happens
Diesel has two jobs on its way through an engine. Before it burns, it lubricates — and then it ignites. The high-pressure pump and the injectors are made to very fine gaps, and your diesel passing through them is what keeps those surfaces from wearing down against each other.
The second job petrol doesn't do at all, and the first it does poorly. The clattering comes from petrol being designed not to ignite when compressed, which is exactly the opposite of what a diesel needs. On top of that it is thinner than diesel, it strips out the lubrication the system rests on, and any pump running on that blend is wearing itself.
Taken together, they show the shape the issue takes. It's movement that does the damage, not contact. All a tank with petrol in it amounts to is a fuel fault. The beginning of a mechanical problem is a pump that has been running on that petrol — and whatever a worn pump sheds travels on with your fuel to your injectors beyond it.
Culnady, petrol in a diesel: four cases, from mild to serious
Fuelled but not once started — the best it gets. That petrol is inside the tank and just that tank, and the task is a drain and a flush where your car sits. This is the one scenario that can only truly occur on a forecourt, since anywhere else your car has been driven to get there.
Started for a moment, or only your ignition on. Once primed, the fuel system has drawn petrol from your tank up to your filter and the lines. Usually little more than clearing, purging and seeing to the filter, so still simple.
Your pump now spent a few miles on diluted fuel — that's what driving the car does. Tank, lines, filter, then clean fuel run through the entire system: that is this work, and the way the vehicle was driven matters as much as the distance. Driving the children to the local primary school is one kind of trip. Getting as far as Derry, under 50 miles away, makes a very different task — as does any distance on the M77, over 50 miles from Culnady, with the engine working hard all the way.
Clattering, a lumpy idle, smoke, a throttle gone soft: driven until it complained. The engine is telling you the fuel is no longer acting like diesel. Pull up on the spot — on the verge on Wallace Cottages, at the kerb, down a side road — and don't move it. Permanent damage is very unusual if a vehicle is stopped early, and the drain and flush that still come first deal with it.
What Culnady drivers get told about petrol in a diesel — and the stories in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Topping up removes nothing; it gives you a bigger tank of the same mix. The assumption behind the advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Newer diesels can handle a little petrol" — a myth, and closer to the opposite. Protection matters more on modern diesels, not less, since their fuel passes through finer parts at higher pressure.
Myth: "If it starts and drives, there's no damage done." This is the one that fools people. Feed diesel to a petrol motor and it usually won't run, so the driver stops — and the harm stops with them. Feed petrol to a diesel and it usually fires up, ticks over and pulls away as if nothing happened — all the while its pump wears. 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 different fault. It doesn't put back what petrol has diluted, and that petrol is still inside your tank afterwards.
If the engine has been run, part of that petrol is in the filter and the lines, not the tank — and the next start sends it straight back through the pump. So the myth "drain the tank yourself and you are sorted" does not stand up. It is also genuinely hazardous to drain petrol into a can by the roadside.
Petrol in a diesel: how does it happen?
Nobody does it on purpose, and it's seldom carelessness. The forecourt makes it simple: the petrol nozzle is the slimmer of the two, and it slides into a diesel filler with almost no resistance, while a diesel nozzle generally will not go into a petrol car at all. So the mistake runs one way.
When habit and the car stop matching, it occurs. A new motor, a hire car or a courtesy car. Two vehicles on one driveway, one petrol, one diesel. Your usual forecourt, its pumps now in a different order. A rushed fill en route to the nearest station with a train to catch. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is precisely the moment it takes place. Throw in a back seat full of children, a phone call or rain, and habit wins.
Next time you fill up around Culnady: preventing petrol in a diesel
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most usually do. Check the pump's label; the colour is just a clue.
- Inspect your filler flap. Many motors state the fuel inside the flap or on the cap. Look at it on your first fill in any motor you do not know.
- Label your key. In a home with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember.
- It sounds daft and it works: on the first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the pump.
- While you're thinking about something else, this is an easy mistake to make — so tuck the phone away.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to block a petrol nozzle, and add-on devices exist for motors without one. They are a backstop, not a reason to stop checking the pump.
- Spotting it halfway? Stop there and then. A weaker blend follows from less petrol in your tank, but your next step stays the same: do not fire it up.
Culnady: already put petrol in a diesel?
Short and simple, then, is the order of things. Starting it is out, and so is turning on the ignition. Ask the attendants to help you roll it clear of the petrol pump if you are still on the forecourt, whether that is the nearest petrol station or anywhere else. Phone 0333 366 0103 next, with three answers — your fuel, the approximate volume, and if it has run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a separate fault — Culnady has a page just for it.
What makes one Culnady petrol in a diesel task cost more than the next
Four different tasks sit behind the four situations above — which is why there's no honest single price. The situation itself does most of the work of moving the cost. Where the car is counts too, and whether a van can safely get to it, after the proportion of petrol to what the tank holds.
What got in, how much, and whether it's run — three questions we ask before costing, not after, for precisely that reason. Given those replies, you get a straight figure rather than a range.
About Culnady and where it is
Culnady is a small locality in County Londonderry, situated inland at an elevation of around 50 metres. Culnady lies near the villages of Upperlands and Maghera, and is approximately 28 miles from the city of Derry. Culnady is characterised by its predominantly detached housing stock, reflecting its rural setting. Culnady is a relatively small community, with a population of around 658 people.
Fuel drain cover in Culnady and across County Londonderry
Culnady waits in the BT postcode area, and the vans that answer petrol in diesel jobs there work the locations around it as well — Upperlands, Gulladuff and Maghera among them. The car doesn't need to come to us: our engineers drain on a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
In Culnady and still at the petrol pump?
Nothing beats it: that is where you now are. Keep it off. Call.