Petrol in a Diesel Car in The Ham: How Worried Should You Be?
Far less than you likely are, provided it has not been started. "Have I wrecked it?" is the first question everyone around The Ham asks, and the truthful answer is usually no, since petrol resting in a diesel tank harms nothing until it's drawn through the system — by ignition priming, by the starter, or by driving. Leave the motor off and phone Petrol in Diesel — that is how you keep it like that. The rest of this page explains 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 a second time.
What petrol in a diesel does to your engine
Passing through a motor, diesel is doing two jobs at the same time. It protects to begin with, and after that does it burn. Extremely fine tolerances go into the injectors and the high-pressure fuel pump, and only the diesel running through keeps their surfaces from grinding together.
Petrol does the first task badly and the second not at all. It's runnier than diesel and takes away the protection the system rests on, 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 is where the knocking comes from.
Put these together and the shape of the problem is plain. Contact doesn't do the harm — circulation does. Petrol in a tank is a fuel issue. Whatever a worn pump sheds goes on, borne 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.
Petrol in a diesel around The Ham: how bad is it? Four cases
Fuelled but not once started — as good as it gets. Just the tank has petrol in it, and so the task is clearing the tank and rinsing the system where the car stands. This situation can only truly take place at a forecourt: anywhere else, the vehicle got there by being driven.
The ignition turned on, or a brief start. Your system has been primed, so petrol has left your tank and reached the fuel filter and the fuel lines. Drain, flush, see to the fuel filter: still usually straightforward.
The pump now spent a few miles on thinned fuel — that is what driving the vehicle does. Tank, lines, filter, then clean fuel run through the entire system: that's the work, and the way the car was driven counts as much as the mileage. Short trips, like the school run to Westbury Church of England Junior School, are one thing. A run as far as Bath, under 15 miles away, is a very different task. So is any mileage on the M4, under 25 miles from The Ham, where the motor has been working hard throughout.
Driven until it complained. Knocking, an uneven idle, smoke, a throttle that has gone soft. The fuel isn't acting like diesel any more, and the engine is telling you. Stop wherever you are — the verge on Station Road, a lay-by, a side street — and leave the vehicle where it is. A vehicle pulled over soon very seldom has lasting damage, since the drain and the flush-through, which still go first, sort it out.
Stories The Ham motorists hear about petrol in a diesel
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing is removed by topping up — you are left with a bigger tank, still the same mixture. The assumption behind the guidance — that diesel fuel systems accept petrol by percentage — is wrong.
If anything, the reverse holds. Myth: "A newer diesel can cope with a bit of petrol." Lubrication matters more on newer diesels, not less, since their fuel passes through smaller components at higher pressure.
This is the one that fools drivers. Myth: "If it starts and drives, there is no harm done." Feed diesel to a petrol engine and it generally will not run, so the driver stops — and the damage stops with them. Feed petrol to a diesel and it normally starts, idles and pulls away as if nothing happened — all the while its pump wears. Running isn't the same as fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a separate issue. The petrol is still inside the tank after that, and what it has weakened is not put back.
"Drain it yourself and you're sorted" — a myth, since after it's been running some petrol sits in the fuel filter and lines, waiting to go right back through your pump on your next start. Draining petrol into a can at the roadside is also truly dangerous.
Why petrol in a diesel happens at all
On purpose? Never. Through carelessness? Rarely, if ever. The petrol nozzle is the smaller of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol motor at all. The forecourt makes it simple, and the slip runs one way.
The moment routine stops matching your car is the moment it happens. Hire cars, courtesy cars, and vehicles that are new to you. One petrol and one diesel on the drive of the same household. A forecourt you know, but with its pumps laid out differently. A rushed fill en route to Westbury 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. Throw in a back seat full of kids, a phone call or rain, and habit wins.
The Ham drivers: how to avoid petrol in a diesel next time
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, but not on every forecourt. The label is what counts.
- In a car you do not know, look inside the flap over the filler or at the cap before the first fill: plenty of vehicles state the fuel there.
- A coloured fob or a sticker on the diesel's key achieves more than any amount of intending to remember, in a household with one of each.
- Before the nozzle comes off the pump the first time you fill a hired or new motor, say "diesel" aloud. Daft, perhaps, but it works.
- Thinking about something else is when this becomes an easy mistake to make, and so put your phone away and keep your mind on the pump.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler designed to refuse a petrol nozzle, and add-on devices exist for the remainder. Treat it as a backstop, then keep checking the pump.
- Spotting it mid-fill? Stop there and then. A weaker blend results from less petrol inside that tank, but your next stage remains the same: do not crank it.
Petrol already in a diesel in The Ham? Start here
Then, there's only a short order of things. Do not turn the ignition on, and do not crank it. If you are still at the forecourt — Esso or anywhere else — ask the attendants to help you push the car clear of the pump. What got in, about how much, and if it has run: tell us that when you phone 0333 366 0103.
Say so if it was AdBlue rather than petrol: it is a different issue, with its own page for The Ham, because AdBlue brings corrosion and deposits rather than lost protection.
Why one petrol in a diesel task around The Ham costs more than another
A fair single price doesn't exist here: four situations, four separate tasks. Chiefly, the cost shifts with which situation you're in. Next it's the share — how much petrol got in against how much that tank holds — and after that where the vehicle is and whether our van can reach it safely.
Ahead of any quote, not after, come three questions: your fuel that got in, the amount, and whether it's run. That's why. With the answers, you get a straight figure rather than a range.
About The Ham, briefly
The Ham is a suburban area in Wiltshire, situated on the riverside at an elevation of 71 metres, with semi-detached housing being the predominant type of accommodation. The Ham lies near the city of Bath, approximately 10 miles away, and is also close to nearby places such as Hawkeridge, Westbury, and Penleigh. The Ham has a population of around 2030 residents, making it a relatively small community. The Ham is located in the South West region of England, about 91 miles from London.
Fuel drain cover across Wiltshire, The Ham included
Petrol in diesel calls in The Ham — part of the BA postcode area — go to teams that likewise cover the locations around it, Hawkeridge, Westbury and Penleigh among them. Our technicians 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.
The Ham: still at the pump?
No position is better: that is where you are. Turned off it remains; then phone.