How Worried Should You Be? Petrol in a Diesel Car in Tir-y-berth
Less than you probably are, if it hasn't been started. Until your ignition primes your pump, your starter cranks, or the car is driven, petrol in a diesel tank simply rests there and does no harm. Which means the truthful reply to that first Tir-y-berth question — "have I ruined it?" — normally no. Keep it that way: leave your motor off then phone Petrol in Diesel. Keep reading for three things: the effect petrol has inside a diesel engine, the clues of how far it has got, and the way to make sure you never repeat it.
What petrol in a diesel does to the engine
Diesel has two tasks on its way through a motor. Before it ignites, it protects — then it combusts. Your high-pressure pump and the injectors are made to very fine gaps, and your diesel passing through them is what stops those surfaces from wearing down against one another.
The second task petrol does not do at all, and the first it does badly. The clattering comes from petrol being made not to ignite when compressed, which is precisely the reverse of what a diesel needs. On top of that it is thinner than diesel, it strips away the lubrication your system hinges on, and any pump working on that mix is wearing itself.
Combined, those leave the shape of the problem plain. It's movement that does the damage, not contact. Where the petrol is only in your tank, it's a fault of fuel, nothing more. Whatever a worn pump sheds goes on, carried by your fuel, into the fuel injectors further along, which is why a pump that has worked on that petrol is where a mechanical issue starts.
How bad is petrol in a diesel? Four situations our technicians see around Tir-y-berth
Filled up, and not started: no case is better. At a forecourt, and genuinely only there, that petrol is still limited to your tank — because everywhere else the car was driven to get to it. The job is emptying and purging on the spot.
A moment's running, or just the ignition on. Petrol has left your tank and reached the fuel filter and the fuel lines, since the fuel system has been bled. Drain, flush, deal with the fuel filter: still normally simple.
Some miles driven, and your pump has spent each of them labouring on diluted fuel. Miles is only half of that; how hard it was driven counts equally. Either way this work runs to that tank, the lines, the filter and fresh fuel through the whole system. On the school run to the local primary school, the distance is short. Driving as far as Newport, under 15 miles away, makes a very different job — as does any miles on the M4, under 10 miles from Tir-y-berth, with the engine working hard all the way.
It protested, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone lumpy. What you are hearing is your engine reporting fuel that no longer behaves like diesel. Pull up where you are — on the verge on New Road, at the kerb, down a side road — and do not move it again. The fuel drain and flush still come first, and they take care of it: if a car is stopped soon, lasting damage is very uncommon.
What Tir-y-berth drivers get told about petrol in a diesel — and the myths in it
Myth: topping up to full with diesel makes it fine. It doesn't. Nothing is removed by topping up — you're left with a fuller tank, still the same mixture. A diesel fuel system doesn't tolerate petrol by percentage in the way that guidance supposes.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the opposite. Protection counts more on modern diesels, not less, since their fuel runs through finer components at higher pressure.
The myth that catches drivers off guard: if it starts and drives, it must be unharmed. Diesel in a petrol motor generally leaves a motor that won't run: the driver stops, and so does the damage. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually will; meanwhile the pump grinds. Fine and running are not the same thing.
Myth: a two-stroke additive makes it safe to drive home. It was an old workaround, supposed for another fault. It doesn't put back what petrol has diluted, and the petrol is still inside that tank afterwards.
If the motor has run, part of the petrol sits in the fuel filter and your lines, not your tank — and the next start sends it right back through your pump. So the myth "drain the tank yourself and you're sorted" doesn't hold. Besides, petrol emptied into a can by the road is genuinely risky.
How it happens: petrol in a diesel
Nobody does it on purpose, and it is seldom carelessness. A diesel nozzle mostly won't go into a petrol vehicle, but the slimmer petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one mistake straightforward, and just in that direction.
It happens when routine and the vehicle stop matching. A vehicle that's new to you — hired, on loan as a courtesy car, or just bought. Households running one of each, petrol and diesel. A familiar forecourt with the pumps in a different order. A train to catch, and a rushed fill en route to Pengam. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist accustomed to petrol: precisely when it happens. Throw in a back seat full of kids, a phone call or rain, and the hand wins.
How to prevent petrol in a diesel on your next fill-up in Tir-y-berth
- Check the pump, not the colour. In the UK unleaded handles are generally green and diesel black, yet not on each forecourt. The label is what counts.
- In a vehicle you don't know, look inside the flap over your filler or at the cap before the first fill: many motors state the fuel type there.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of meaning to remember, for a home with one of each.
- It seems 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 petrol pump.
- Put the phone away. This is an easy mistake to make whilst you're thinking about something else.
- Some diesels have a filler designed to block a petrol nozzle, and devices you can add are available for cars without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the petrol pump.
- Less petrol makes a thinner mixture, so stop as soon as you realise — though remembering that your next step is unchanged. It's still not to start the car.
Put petrol in a diesel around Tir-y-berth already?
Then the order of things is short. Starting it is out, and so is turning on your ignition. Ask the staff to help you push it away from the petrol pump if you're still on the forecourt, whether that is the nearest petrol station or somewhere else. Next, 0333 366 0103. We will ask what was put in, roughly how much, and if it has been run.
Say so if it was AdBlue instead of petrol: it is a different problem, with its own page for Tir-y-berth, because AdBlue brings corrosion and deposits instead of lost protection.
Tir-y-berth petrol in a diesel jobs: why one costs more than another
There's no honest single quote for this, since the four situations above are four separate tasks. Mostly, your cost shifts with which situation you're in. After that it is the ratio — how much petrol was put in against how much that tank takes — and after that where the vehicle is and whether a technician can reach it safely.
Ahead of any quote, not after, we ask three questions: the fuel that went in, the volume, and whether it's run. That's why. A range becomes a straight figure once those replies are in.
About Tir-y-berth and its setting
Tir-y-berth is a small village in Caerphilly, situated on the banks of a river at an elevation of 147 metres. Tir-y-berth has a mix of housing types, but is predominantly characterised by terraced homes. Tir-y-berth is located near other villages such as Pengam, Fleur-de-lis, and Glan-y-nant, and is approximately 11 miles from Newport. Tir-y-berth has a population of around 1622 residents.
Tir-y-berth and Caerphilly: where our fuel drain cover runs
Petrol in diesel call-outs in Tir-y-berth — part of the CF postcode area — go to teams that likewise cover the spots about it, Pengam, Fleur-de-lis and Glan-y-nant among them. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations our technicians work, and the vehicle doesn't need to move to us.
Tir-y-berth: still at the pump?
Then you are in the best position there can be. Phone, and keep it turned off.