Whetstone: Petrol in a Diesel Car? How Worried to Be
If it hasn't been started, worry far less than you likely are. Petrol resting in a diesel tank does nothing to your motor until something draws it through your fuel system — the ignition priming the pump, your starter, or driving on its own. So the fair answer to the first query everyone around Whetstone asks, "have I wrecked it?", is usually no. To leave the vehicle that way, ring Petrol in Diesel and leave the engine switched off. Below, you will find what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to your engine?
Two jobs fall to diesel on its journey through a motor. Before it burns, it lubricates — then it combusts. The high-pressure fuel pump and the injectors are designed to very fine clearances, and the 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 badly. It's thinner than diesel and takes away the protection your fuel system hinges on, and so a pump running on a petrol blend 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 rattling comes from.
The shape of the problem is clear when you put those together. It's movement that does the harm, not contact. A tank with petrol in it is a fuel fault. Whatever a worn pump sheds goes on, carried by your fuel, into the injectors downstream, which is why a pump that has been working on the petrol is where a mechanical problem begins.
Four situations our engineers see in Whetstone: how serious is petrol in a diesel?
Fuelled but never started — the best it gets. The petrol is in your tank and only your tank, and the job is a drain and a flush where the car sits. This is the one scenario that can only really take place on a forecourt, as anywhere else your car has been driven to get there.
Your ignition switched on, or a short start. Petrol has left that tank and reached the fuel filter and the fuel lines, because the system has been bled. That's usually still an easy job — a drain, a flush, and the filter seen to.
Those few miles on the road meant the pump working on fuel diluted by petrol the whole way. The work is your tank, the fuel lines, your filter and fresh fuel through the entire circuit, and how hard the vehicle was driven counts as much as how far. Driving the kids to St Peter's Church of England Primary School Whetstone is one sort of trip. Very different once more: a run to Leicester, under 5 miles away, or any mileage on the M1, under a mile from Whetstone, where the engine kept labouring hard.
Driven on until it complained — rattling, smoke, a ragged idle, a dead throttle. The engine is telling you your fuel is no longer behaving like diesel. Pull up wherever you are — the verge on Wale Road, a lay-by, a side street — then leave the vehicle there. The drain and flush still go first, and they deal with it: when a vehicle is stopped quickly, long-term damage is very unusual.
What Whetstone motorists get told about petrol in a diesel — and the myths in it
False: topping up to full with diesel makes it fine. It doesn't. Nothing is removed when you top up — the tank simply carries more of the same blend. Percentage is not how a diesel fuel system copes with petrol, whatever that advice presumes.
If anything, the opposite holds. Myth: "A newer diesel can cope with a bit of petrol." A current diesel sends its fuel through more precise components at higher pressure, which makes the lubrication count more, not less.
"It starts, it drives, and so there is no harm" — the myth that catches most motorists than any other. A petrol motor fed diesel usually will not run, and so the driver stops and the damage stops with them. Feed petrol to a diesel and it usually starts, idles and pulls away as if nothing has happened — all while its pump wears. Running doesn't mean fine.
An outdated fix for a different problem is behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." That petrol is still inside your tank afterwards, and what it has weakened is not put back.
"Drain it yourself and you're sorted" — a myth, since after it has been running some petrol sits in the filter and lines, waiting to go straight back through your pump at the next start. Besides, petrol emptied into a can by the road is truly hazardous.
How does petrol in a diesel occur?
Nobody does it on purpose, and it's rarely 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 won't go into a petrol vehicle at all. So the slip runs one way.
When routine and the vehicle stop matching, it occurs. A new motor, a hire car or a courtesy car. One petrol and one diesel on the drive of the same household. A well-known forecourt with the pumps in a different order. A hurried fill on the way to Narborough with a train to catch. Years of petrol motors behind you, a diesel Renault Megane in front of you at the forecourt for its first tank — that is when. Add a back seat full of children, a phone call or rain, and the hand wins.
Next time you fill up in Whetstone: avoiding petrol in a diesel
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most usually do. Check the petrol pump's label; the colour is only a hint.
- Plenty of vehicles state the fuel type inside your filler flap or on the cap, and so check there on your first fill in a car you don't know.
- Label your key. In a household with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember.
- "Diesel", out loud, before you lift the nozzle — each time a new or hired car needs its first tank. It seems daft. It does the trick.
- Tuck your phone away. This is an easy mistake to make while you are thinking about something else.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler designed to reject a petrol nozzle, and add-on devices are available for motors without one. They are a safety net, not a reason to stop checking the pump.
- As soon as you notice, stop: less petrol inside your tank makes a weaker blend. What to do next does not change, though — still do not start the car.
Petrol already in a diesel in Whetstone? Start here
The order of things is brief, then. Leave it unstarted, with your ignition off as well. The staff on the forecourt — whether at Texaco itself or wherever you filled up — will usually help push it clear of the petrol pump if you ask. What was put in, about how much, and if it's run: tell us those when you call 0333 366 0103.
Corrosion and deposits form the issue with AdBlue, where petrol brings lost protection. So if it was AdBlue, say so — and see its own Whetstone page.
What makes one Whetstone petrol in a diesel job cost more than the next
The four scenarios above are four different tasks, so no single quote for this would be fair. Which of them you're in is mostly what shifts your cost. The ratio matters next, meaning how much of your tank is petrol, and then the location of the vehicle and whether getting to it is safe for a van.
That is why we ask three queries before costing rather than after: what went in, how much, and whether it has run. Given those replies, you get a straight figure rather than a range.
About Whetstone itself
Whetstone is a village in Leicestershire, situated on the banks of the River Soar, with an elevation of around 71 metres. Whetstone lies close to the city of Leicester, approximately 4.7 miles to the south, and is near other villages such as Blaby and Narborough. Whetstone has a population of around 2357 people, predominantly living in semi-detached housing. Whetstone is located in the East Midlands region, about 86 miles north of London.
Whetstone and Leicestershire: where our fuel drain cover runs
Petrol in diesel jobs around Whetstone — part of the LE postcode area — go to vans that also cover the places about it, Blaby, Littlethorpe and Narborough among them. We drain wherever your car is — your own drive, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
At the pump in Whetstone, still?
The best position there is, then — that is where you are. Phone, and keep it turned off.