Derrynoose: Petrol in a Diesel Car? How Worried to Be
Not started? Then less worried than you likely are. "Have I ruined it?" is the first thing anyone in Derrynoose asks, and the honest answer is normally no, because petrol left in a diesel tank hurts nothing until it's drawn through your fuel system — by ignition priming, by your starter, or by driving. To keep it that way, phone Petrol in Diesel and leave your engine alone. What petrol really does to a diesel, how to judge how far it's gone, and how to keep it from happening again: that's the remainder of this page.
What petrol in a diesel does to the engine
Passing through a motor, diesel is doing two things at once. It combusts, and before it ignites it lubricates. Built to extremely fine tolerances, the fuel injectors and the pump rely on the diesel flowing through them to stop their surfaces wearing against one another.
The second job petrol does not do at all, and the first it does badly. It's runnier than diesel and removes the protection your fuel system depends 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 reverse of what a diesel needs from its fuel. That is where the rattling comes from.
Put those together and the shape of the problem is clear. The damage is done by circulation, not by contact. All a tank with petrol in it amounts to is a fuel issue. After the pump has been working on that petrol, a mechanical fault has started: whatever is shed by a pump that's wearing is carried onward to the fuel injectors with the fuel.
How bad is petrol in a diesel? Four scenarios we see in Derrynoose
Filled up, not once started. The best case there is. At a forecourt, and truly only there, the petrol is still limited to the tank — since everywhere else the vehicle was driven to get to it. The task is draining and purging on the spot.
Ignition on, or started for a moment. With the system primed, your lines and filter now hold petrol that has come from the tank. Drain, flush, see to the fuel filter: still usually simple.
Those few miles driven were the pump working on fuel weakened by petrol throughout. Tank, lines, filter, then fresh fuel run through the entire circuit: that's the work, and the way your car was driven matters as much as the mileage. Driving the children to the local primary school is one sort of trip. Very different once more: a run to Armagh, under 10 miles away, or some mileage on the M77, over 50 miles from Derrynoose, where the engine kept running hard.
Driven until it complained. Rattling, a lumpy idle, smoke, a throttle that has gone soft. The engine is telling you the fuel is no longer acting like diesel. Whether it's the verge on Heugh Road, a lay-by or a side road, stop where you are then leave it. A car stopped soon very seldom has permanent damage, since the drain and the flush, which still come first, take care of it.
What Derrynoose motorists get told about petrol in a diesel — and the myths in it
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. A bigger tank of the same mixture is all you get, because topping up takes out nothing. A diesel fuel system doesn't tolerate petrol by percentage in the way that advice assumes.
If anything, the opposite holds. Myth: "A newer diesel can cope with a bit of petrol." Lubrication counts more on newer diesels, not less, because their fuel passes through smaller components at higher pressure.
This is the one that fools motorists. Myth: "If it starts and drives, there's no harm done." The motorist of a petrol motor fed diesel normally has no choice but to stop, because it will not run, and the damage stops there. Whilst your pump grinds, a diesel fed petrol normally starts, ticks over and drives away as if nothing has happened. Being able to run is not proof of being fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a separate issue. The petrol is still inside that tank afterwards, and whatever it has diluted isn't put back.
The next start draws petrol back round your pump out of your lines and the filter, where some of that ends up after your engine has been run. That's why a DIY tank drain doesn't leave you sorted — a myth. Also, a can of petrol drained at the kerbside is truly hazardous.
Petrol in a diesel: how does it take place?
Nobody does it on purpose, and it's seldom carelessness. One way only, because of the nozzles: the narrower petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one generally won't fit a petrol motor. That's how the forecourt makes it simple.
When routine and the car stop matching, it takes place. Hire cars, courtesy cars, and motors that are new to you. Two vehicles on one driveway, one petrol, one diesel. A familiar forecourt with the pumps in a different order. Filling up in a hurry on the way to the nearest station, with a train to catch. A new-to-you diesel Volkswagen Passat, its first fuelling, and a driver used to petrol: precisely when it takes place. Throw in rain, a phone call or a back seat full of kids, and your hand repeats what it has always done.
Derrynoose people: how to prevent petrol in a diesel next time
- The label is what counts, so read the petrol pump rather than the colour: in the UK unleaded handles are usually green and diesel black, but not on every forecourt.
- Inspect your filler flap. Plenty of cars state the fuel inside the flap or on the cap. Look at it on your first fill in any car you do not know.
- A coloured fob or a sticker on the diesel's key does more than any amount of intending to remember, in a household with one of each.
- "Diesel", aloud, before you pick up the nozzle — each time a new or hired car gets its first tank. It sounds silly. It does the trick.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck your phone away.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to refuse a petrol nozzle, and add-on devices exist for the rest. Count it as a safety net, then keep reading the petrol pump.
- The moment you notice, stop: less petrol inside your tank makes a thinner mix. What to do next does not change, though — still do not start the car.
Put petrol in a diesel in Derrynoose already?
In that case, there is just a short order of things. Do not crank it, and do not turn the ignition on. Ask the staff to help you push it away from the pump if you're still on the forecourt, whether that is the nearest petrol station or anywhere else. Call 0333 366 0103 next, with three facts — the fuel, the approximate volume, and if it has run.
Say so if it was AdBlue instead of petrol: it's a separate issue, with its own page for Derrynoose, since AdBlue brings corrosion and deposits rather than lost lubrication.
What makes one Derrynoose petrol in a diesel job cost more than the next
Four separate tasks lie behind the four situations above — which is why there's no honest single price. Which of them you're in is chiefly what moves the cost. The proportion matters next, meaning how much of the tank is petrol, followed by the location of the car and whether reaching it is safe for a van.
What was put in, how much, and if it has run — three queries our engineers ask before pricing, not after, for exactly that reason. The answers change a range into a straight figure.
About Derrynoose itself
Derrynoose is a small locality in County Armagh, situated inland at an elevation of around 155 metres. Derrynoose lies approximately 9 miles from the city of Armagh and is close to nearby places such as Keady, Madden, and Darkley. Derrynoose has a population of around 527 people and is characterised by predominantly detached housing.
Derrynoose and County Armagh: where our fuel drain cover runs
Our teams answering petrol in diesel call-outs around Derrynoose, in the BT postcode area, also work the locations around it, Keady, Madden and Darkley included. We drain where the vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
Derrynoose: still at the pump?
Then, you couldn't be in a better spot. Keep it off. Call.