Hempnall: Petrol in a Diesel Car? How Worried to Be
Provided it hasn't been started, you can worry far less than you likely are. Until the ignition primes the pump, your starter turns, or your car is driven, petrol in a diesel tank just waits there and does no harm. Which means the honest reply to that first Hempnall question — "have I ruined it?" — usually no. Leave the motor off and phone Petrol in Diesel — that is how you keep it like that. Below, you will find what petrol really does inside a diesel, how far it may have got, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to the motor?
Diesel has two jobs on its way through a motor. Oiling comes before burning; it does both. Extremely fine gaps are built into the injectors and the high-pressure pump, and just your diesel running through keeps those surfaces from grinding together.
Badly at the first, not at all at the second: that is petrol. It is runnier than diesel and removes the protection the fuel system depends 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 trouble is plain when you put those together. It is circulation that causes the harm, not contact. All a tank with petrol in it amounts to is a fuel fault. Whatever a worn pump sheds goes on, carried by your fuel, into your injectors further along, which is why a pump that has been working on that petrol is where a mechanical issue starts.
Four situations our technicians see around Hempnall: how bad is petrol in a diesel?
Filled up, and never started: nothing beats it. That petrol is inside your tank and only the tank, and the task is a drain and a flush where the vehicle stands. This is the one situation that can only truly occur on a forecourt, because anywhere else your car has been driven to get there.
Your ignition turned on, or a brief start. The fuel system has been bled, so petrol has left that tank and got to the filter and the fuel lines. Drain, flush, deal with the fuel filter: still usually straightforward.
Driven a few miles. Now your pump has spent these miles labouring on thinned fuel. Mileage is only half of it; how hard it was driven matters equally. Either way this work runs to the tank, the lines, the fuel filter and clean fuel through the entire system. The school run to Hempnall Primary School is one thing. A run as far as Norwich, under 10 miles away, is a very different job. So is any mileage on the M11, over 50 miles from Hempnall, where your engine has been labouring hard the whole time.
It protested, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone ragged. The fuel is not acting like diesel any more, and the motor is telling you. Whether it is the verge on Bussey's Loke, a lay-by or a side road, stop there and leave it. A car stopped quickly very rarely has permanent damage, because the fuel drain and the flush-through, which still come first, deal with it.
Myths Hempnall motorists hear about petrol in a diesel
False: topping up to full with diesel makes it fine. It does not. Nothing is removed by topping up — you're left with a fuller tank, still the same mixture. A diesel fuel system does not tolerate petrol by percentage in the way that guidance assumes.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the opposite. Lubrication counts more on newer diesels, not less, because their fuel passes through smaller components at higher pressure.
This is the one that fools people. Myth: "If it starts and drives, there's no damage done." Diesel in a petrol motor generally means a motor that will not run: the driver stops, and so does the damage. Whilst the pump grinds, a diesel fed petrol usually starts, ticks over and drives away as though nothing has happened. A running engine does not mean fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a distinct issue. What petrol has diluted stays diluted, and the petrol stays in the tank anyway.
"Drain it yourself and you're sorted" — a myth, because after it's been running some petrol lies in the fuel filter and lines, ready to go straight back through your pump on your next start. It's also really hazardous to drain petrol into a can by the roadside.
Why petrol in a diesel takes place at all
Nobody does it on purpose, and it's rarely carelessness. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle generally will not go into a petrol car at all. So the slip runs one way.
When habit and the car stop matching, it happens. A new vehicle, a hire car or a courtesy car. One petrol and one diesel on the driveway of the same household. A forecourt you know, only with its pumps arranged differently. A train to catch, and a hurried fill en route to Norwich. Years of petrol cars behind you, a diesel Renault Clio in front of you on the forecourt for its first tank — that's when. Throw in rain, a phone call or a back seat full of children, and the hand repeats what it has always done.
Avoiding petrol in a diesel next time you fill up in Hempnall
- Green for unleaded and black for diesel is normal in the UK — yet not on every forecourt. Trust the label on the pump, not the colour.
- The first fill in a strange motor is the time to check your filler flap — inside it, or on the cap, plenty of motors state the fuel to use.
- Mark 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 intending to remember.
- It sounds silly and it does the trick: on your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the pump.
- Mistakes like this are straightforward to make whilst your mind is on something else, so the phone goes away.
- Some diesels have a filler designed to block a petrol nozzle, and devices you can add exist for vehicles without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop reading the petrol pump.
- As soon as you realise, stop: less petrol inside that tank makes a thinner mix. What to do next doesn't change, though — still do not start the vehicle.
Put petrol in a diesel around Hempnall already?
Then the order of things is short. Starting it is out, and so is turning on the ignition. Ask the staff to help you push it away from the petrol pump if you are still at the forecourt, whether that's the nearest petrol station or somewhere else. Next, 0333 366 0103. We'll ask what went in, roughly how much, and if it's been run.
If it was AdBlue rather than petrol, say so. That is a different issue — corrosion and deposits rather than lost protection — and it has its own page for Hempnall.
Hempnall petrol in a diesel tasks: why one costs more than another
An honest single price does not exist here: four situations, four separate jobs. Which of them you are in is mostly what shifts the cost. The proportion matters next, meaning how much of that tank is petrol, and then the location of the car and whether getting to it is safe for a technician.
What got in, how much, and whether it's run — three queries our technicians ask before costing, not after, for precisely that reason. A range turns into a straight figure once the answers are in.
About Hempnall, for a moment
Hempnall is a small village in south Norfolk, situated approximately 8.7 miles south of Norwich and 91.7 miles northeast of London. Hempnall sits in a low-lying area at an elevation of around 32 metres, surrounded by other small settlements such as Hempnall Green and Saxlingham Green. Hempnall has a population of around 633 people, predominantly living in semi-detached houses.
Fuel drain cover in Hempnall and across Norfolk
Petrol in diesel jobs around Hempnall — part of the NR postcode area — go to teams that likewise cover the locations around it, Hempnall Green, Saxlingham Green and Lundy Green among them. A forecourt, a supermarket car park, a lay-by or your own drive are all spots our engineers work, and your vehicle doesn't need to move to us.
Hempnall: still at the petrol pump?
Then, you could not be in a better spot. Keep it off. Ring.