Woodend: Petrol in a Diesel Car? How Worried to Be
Likely less than you already are — as long as nobody has started the car. Everyone in Woodend begins with "have I wrecked it?", and the honest answer is generally no: petrol left in the tank of a diesel stays harmless until priming, cranking or driving draws it into your fuel system. Leave your engine off then phone Petrol in Diesel — that keeps it like that. The remainder of this page explains what petrol really does to a diesel, how to tell how far it has got, and how to make sure it does not happen to you again.
Inside the engine: what petrol in a diesel does
Passing through an engine, diesel does two things at once. It burns, and before it ignites it protects. Very fine clearances go into the fuel injectors and the high-pressure fuel pump, and only the diesel flowing through keeps their surfaces from grinding together.
The second job petrol doesn't do at all, and the first it does badly. A pump working on a petrol mixture is wearing itself out, because petrol is thinner than diesel and strips out the lubrication your fuel system depends on. Petrol is also designed to resist igniting under compression — the reverse of what a diesel wants from its fuel — and that is where any rattling comes.
The shape of the problem is plain once you put those together. The damage is done by circulation, not by contact. A tank with petrol in it is a fuel issue. The start of a mechanical one is a pump that has been working on that petrol — and whatever a worn pump sheds moves on with the fuel to your injectors downstream.
Four scenarios our engineers see around Woodend: how serious is petrol in a diesel?
Fuelled up, never started. The best case there is. Only your tank has petrol in it, and so the task is emptying your tank and flushing the fuel system where the car stands. This situation can only really occur on a forecourt: anywhere else, the car got there by being driven.
Ignition on, or started for a moment. Petrol has come out of the tank and reached the fuel filter and the fuel lines, since the system has been primed. Drain, flush, see to your filter: still usually easy.
Driven a few miles. Now your pump has spent those miles working on thinned fuel. Distance is only half of it; how hard it was driven counts equally. Either way the work includes your tank, the fuel lines, the fuel filter and fresh fuel through the entire system. Short trips, such as the school run to the local primary school, are one matter. A run as far as Dunfermline, under 10 miles away, is a very different task. So is any distance on the M90, under 5 miles from Woodend, where your engine has been running hard throughout.
Driven until it protested. Rattling, a lumpy idle, smoke, a throttle that has gone soft. What you are hearing is your motor signalling fuel that no longer runs like diesel. Stop wherever you are — the verge on Woodend Road, a lay-by, a side street — and leave the vehicle there. What goes first is still the drain and flush-through, and that sorts it out, with lasting damage very rare if a vehicle is stopped soon.
What Woodend drivers get told about petrol in a diesel — and the myths in it
"Top it up the rest of the way with diesel and it will be fine" — a myth. It will not. Nothing is removed by topping up — you are left with a fuller tank, still the same mixture. The assumption behind the advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Modern diesels can handle a little petrol" — a myth, and nearer the reverse. A modern diesel sends its fuel through more precise parts at higher pressure, which makes the protection count more, not less.
This is the one that fools motorists. Myth: "If it starts and drives, there is no harm done." Any petrol motor fed diesel generally won't run, so the motorist stops and the harm stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually does; meanwhile the pump grinds. A running engine doesn't mean fine.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an old workaround for a distinct issue. It doesn't put back what petrol has diluted, and that petrol is still in your tank after that.
Once the engine has been run, part of that petrol is in the fuel filter and the lines, not that tank — and your next start pulls it right back through your pump. So the myth "drain that tank yourself and you're sorted" doesn't stand up. It is also really dangerous to drain petrol into a can by the kerbside.
Why petrol in a diesel happens so easily
It's seldom carelessness, and no one does it on purpose. A diesel nozzle mostly will not go into a petrol car, yet the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake simple, and just in that direction.
The moment routine stops matching the vehicle is the moment it occurs. Hire cars, courtesy cars, and cars that are new to you. Households running one of each, petrol and diesel. A forecourt you know, but with its pumps arranged differently. A hurried fill on the way to Cardenden with a train to catch. Years of petrol cars behind you, a diesel Volkswagen Golf in front of you at the forecourt for its first tank — that's when. With rain, a call coming in, or children to deal with, the hand just does what it always has.
Preventing petrol in a diesel next time you fill up around Woodend
- Read the petrol pump, not the colour. In the UK unleaded handles are generally green and diesel black, but not on every forecourt. The label is what counts.
- Check your filler flap. Plenty of motors state the fuel type inside the flap or on the cap. Look at it on the first fill in a motor you don't know.
- A coloured fob or a sticker on your diesel's key achieves more than any amount of intending to remember, in a house with one of each.
- Before the nozzle comes off the petrol pump the first time you fuel a hired or new car, say "diesel" aloud. Daft, perhaps, but it does the trick.
- Thinking about something else is when this becomes an easy mistake to make, so put the phone away then keep your mind on the petrol pump.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler built to block a petrol nozzle, and add-on devices are available for the rest. Treat it as a safety net, then keep checking the petrol pump.
- Stop as soon as you notice. Less petrol in your tank makes a thinner blend. It does not change what to do next, which is still not to crank it.
Already put petrol in a diesel around Woodend?
In that case, there's only a short order of things. Do not start the vehicle, and do not turn your ignition on. Yet at the forecourt, at the nearest petrol station or anywhere else? Ask the staff to help you roll the car clear of the petrol pump. Phone 0333 366 0103 next, with three answers — your fuel, the rough quantity, and if it's run.
If it was AdBlue instead of petrol, say so. That is a separate issue — corrosion and deposits rather than lost lubrication — and it has its own page for Woodend.
One petrol in a diesel task in Woodend costs more than another. Why?
The four scenarios above are four separate jobs, so no single quote for this would be honest. Mostly, the cost shifts with which situation you're in. Two things follow that: the petrol that got in as a share of what your tank takes, then the place the vehicle is in and whether a van can reach it safely.
Before any quote, not after, come three queries: the fuel that went in, the volume, and whether it has run. That is why. Those replies turn a range into a straight figure.
About Woodend itself
Woodend is a suburban area situated on the riverside in Fife, with a mix of detached housing and a relatively small population of around 827 residents. Woodend sits at an elevation of 96 metres, close to the nearby settlements of Auchterderran, Bowhill, and Jamphlars. Woodend is located near the city of Dunfermline, which is approximately 9.3 miles away, and is part of the wider Fife region. Woodend offers a tranquil setting, being some distance from major cities, with London over 345 miles to the south.
Woodend and Fife: where our fuel drain cover runs
Auchterderran, Bowhill and Jamphlars are among the places near Woodend that the same teams work, answering petrol in diesel jobs across Woodend's KY postcode area. The car does not need to come to us: our technicians drain on a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Still at the pump in Woodend?
Then you are in the best place there can be. Ring, and leave it turned off.