Petrol in a Diesel Car in Tranch: How Worried Should You Be?
If it has not been started, worry far less than you likely are. Till your ignition primes the pump, your starter turns, or your car is driven, petrol in a diesel tank just sits there and does nothing. Which means the honest reply to the first Tranch question — "have I wrecked it?" — normally no. Keep it like that: leave your engine off then phone Petrol in Diesel. The remainder of this page sets out what petrol really does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
Petrol in a diesel: what does it do to your engine?
Passing through a motor, diesel is doing two things at once. It protects first, and after that does it burn. The high-pressure fuel pump and the fuel injectors are made to extremely fine gaps, and your diesel passing through them is what keeps those surfaces from wearing down against one another.
Petrol handles the first job poorly and the second not at all. A pump running on a petrol mix is wearing itself out, since petrol is thinner than diesel and strips out the lubrication the fuel system depends on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that is where any clattering comes.
Together, those make the shape of the issue plain. Not contact but circulation is what does the damage. All a tank with petrol in it amounts to is a fuel problem. A pump that has been running on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with the fuel to your injectors further on.
Four scenarios we see in Tranch: how bad is petrol in a diesel?
Filled up, not once started. The best case there can be. Only the tank has petrol in it, so the task is draining the tank and cleaning the fuel system where your car stands. This scenario can only really happen on a forecourt: anywhere else, the car got there by being driven.
Ignition on, or started for a moment. Petrol has come out of that tank and reached your filter and your lines, since the system has been bled. Drain, flush, see to your filter: still normally easy.
Some miles driven, and the pump has spent every one of them labouring on thinned fuel. Miles is only half of it; how hard it was driven matters just as much. Either way this work runs to the tank, the fuel lines, the fuel filter and fresh fuel through the entire circuit. On the school run to the local primary school, the distance is small. A run as far as Newport, under 10 miles away, is a very different task. So is any mileage on the M4, under 10 miles from Tranch, where your engine has been labouring hard the whole time.
Driven till it complained. Clattering, a ragged idle, smoke, a throttle that has gone soft. The fuel isn't acting like diesel any more, and the engine is saying so. Leave it wherever it stops: a lay-by, a quiet street, the verge on Twissell's Road. The fuel drain and flush still go first, and they deal with it: when a vehicle is stopped soon, long-term damage is very uncommon.
Stories Tranch drivers hear about petrol in a diesel
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. 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.
Not so: a newer diesel copes with a bit of petrol. If anything, the opposite. Lubrication matters more on current diesels, not less, since their fuel runs through smaller parts at higher pressure.
This is the one that fools motorists. Myth: "If it starts and drives, there's no damage done." The motorist of a petrol engine fed diesel usually has no choice but to stop, since it will not run, and the harm stops with them. While your pump grinds, a diesel fed petrol normally 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, taken from a fix from years ago, for a different fault. That petrol is still in the tank afterwards, and whatever it has weakened isn't put back.
Once the motor has run, part of the petrol sits in the fuel filter and your lines, not that tank — and the next start pulls it right back through the pump. So the myth "drain your tank yourself and you are sorted" doesn't stand up. It's also genuinely hazardous to drain petrol into a can by the kerbside.
Why petrol in a diesel takes place at all
A careless moment is seldom the cause, and nobody means to do it. One way only, because of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, while the diesel one generally won't fit a petrol motor. That is how the forecourt makes it easy.
The moment habit stops matching your car is the moment it takes place. Courtesy car, hire car, or a vehicle that's new. Two vehicles on one drive, one petrol, one diesel. A forecourt you know, only with its pumps arranged differently. Racing for a train outside Pontypool and New Inn and filling up en route. Precisely the moment it happens: after years of driving petrol, a driver fills a diesel Volkswagen Golf for the first time. With rain, a call arriving, or a car full of children to deal with, your hand just does what it has always done.
Tranch drivers: how to prevent petrol in a diesel next time
- Green for unleaded and black for diesel is usual in the UK — yet not on every forecourt. Trust the label on the petrol pump, not the colour.
- In a motor you don't know, look inside the flap over your filler or at the cap before your first fill: many cars state the fuel there.
- A coloured fob or a sticker on your diesel's key does more than any amount of intending to remember, for a household with one of each.
- "Diesel", aloud, before you pick up the nozzle — every time a new or hired car needs its first tank. It sounds silly. It works.
- Put your phone away. This is an easy mistake to make whilst you're thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to block a petrol nozzle, and add-on devices are available for the remainder. Treat it as a backstop, then keep reading the pump.
- As soon as you notice, stop: less petrol in your tank means a weaker blend. What to do next does not change, though — still don't crank it.
Put petrol in a diesel in Tranch already?
Short and simple, then, is the order of things. Starting it is out, and so is turning on your ignition. Yet at the forecourt, at the nearest petrol station or anywhere else? Ask the attendants to help you roll the vehicle away from the pump. Next, 0333 366 0103. We will ask what got in, about how much, and if it's been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a different fault — Tranch has a page just for it.
What makes one Tranch petrol in a diesel task cost more than the next
Four separate tasks sit behind the four situations above — which is why there's no fair single price. Mostly, the cost shifts with which situation you are in. Where the vehicle is counts too, and whether a technician can safely get to it, after the ratio of petrol to what your tank takes.
That's why our engineers ask three questions before costing instead of after: what was put in, how much, and whether it's run. With those answers, there is a straight figure instead of a range.
About Tranch itself
Tranch is a suburban area in Torfaen, situated inland at an elevation of 235 metres, with semi-detached housing being the predominant type of accommodation. Tranch is located near several nearby places, including Lower Race, Sowhill, and Wainfelin, and is approximately 8.2 miles away from Newport. Tranch has a population of around 1841 residents, and its setting provides a relatively quiet environment. Tranch is also within commuting distance to major cities, with London being around 126.4 miles away.
Fuel drain cover across Torfaen, Tranch included
Lower Race, Sowhill and Wainfelin are among the spots around Tranch that the same teams work, answering petrol in diesel call-outs across Tranch's NP postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all places we drain, and your vehicle does not need to come to us.
Tranch: still at the petrol pump?
The best spot there is, then — that's where you are. Keep it off. Ring.