Should You Worry? Petrol in a Diesel Car in Trevithal
Unstarted? Then less anxious than you probably feel. Until the ignition primes the pump, the starter turns, or the vehicle is driven, petrol in a diesel tank just waits there and does no harm. Which means the honest reply to the first Trevithal query — "have I wrecked it?" — usually no. Petrol in Diesel is who to call, with your motor left off, so it stays that way. Further down, you will find what petrol actually does inside a diesel, how far it may have gone, and how to stop it happening to you again.
Inside your engine: what petrol in a diesel does
Diesel does two jobs on its way through a motor. It ignites, and before it ignites it protects. Extremely fine clearances go into the fuel injectors and your high-pressure pump, and just your diesel flowing through stops those surfaces grinding together.
The second task petrol doesn't do at all, and the first it does badly. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump running on the mixture wearing itself. It is also made to resist igniting under compression — the reverse of what a diesel needs — which is why you hear the knocking.
Put these together and the shape of the problem is clear. The damage is done by circulation, not by contact. Where that petrol is only inside your tank, it is an issue of fuel, nothing more. A pump that has been labouring on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the fuel injectors further on.
How bad is petrol in a diesel? Four scenarios our technicians see around Trevithal
Fuelled up, not once started. The best case there is. On a forecourt, and truly only there, the petrol is still limited to the tank — since everywhere else the vehicle was driven to get to it. The job is draining and rinsing on the spot.
The ignition turned on, or a short start. Petrol has come out of the tank and got to the filter and your lines, since the system has been bled. Usually little more than emptying, purging and seeing to the filter, so still easy.
Those few miles driven meant your pump running on fuel thinned by petrol the whole way. Tank, lines, filter, then clean fuel run through the whole circuit: that's the work, and the way the vehicle was driven matters as much as the miles. Driving the children to Mousehole School is one sort of trip. Any mileage on the M5, over 50 miles from Trevithal, means the motor has worked hard throughout, and a run to Truro, under 50 miles away, makes a very different job too.
Driven on till it protested — rattling, smoke, a ragged idle, a dead throttle. What you are hearing is the motor reporting fuel that no longer behaves like diesel. Stop wherever you are — the verge on Parc An Gate, a lay-by, a side street — and leave it where it is. A vehicle pulled over soon very seldom has permanent damage, since the drain and the flush-through, which still go first, deal with it.
Trevithal drivers and the petrol in a diesel stories they hear
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. Nothing is removed by topping up — you're left with a fuller tank, still the same mix. Percentage isn't how a diesel fuel system copes with petrol, whatever that advice presumes.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the reverse. A current diesel runs its fuel through more precise components at higher pressure, which makes the lubrication matter more, not less.
Myth: "If it starts and drives, there's no damage done." This is the one that fools drivers. Feed diesel to a petrol motor and it usually won't run, so the driver stops — and the damage stops with them. Whilst the pump wears, a diesel fed petrol usually starts, idles and drives away as if nothing has happened. Being able to run isn't the same as being fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a distinct fault. None of what petrol thinned gets put back by it — and later, that tank still holds the petrol.
Myth: "Drain your tank yourself and you are sorted." Once the engine has been run, some of that petrol is no longer inside the tank: it is in your filter and the fuel lines, and it goes right back through your pump at the next start. It's also really risky to drain petrol into a can by the roadside.
Petrol in a diesel: how does it occur?
On purpose? Never. Through carelessness? Rarely, if ever. The forecourt makes it easy: the petrol nozzle is the slimmer of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle mostly won't go into a petrol car at all. So the mistake runs one way.
Habit and your car getting out of step is when it happens. A new motor, a hire car or a courtesy car. Two cars on one drive, one petrol, one diesel. The pumps in a different order on a familiar forecourt. Racing for a train at Penzance and fuelling up en route. Years of petrol motors behind you, a diesel Renault Megane in front of you on the forecourt for its first tank — that is when. Add rain, a phone call or a back seat full of children, and your hand does what it has always done.
Trevithal motorists: how to prevent petrol in a diesel next time
- Green for unleaded and black for diesel is usual in the UK — but not on each forecourt. Trust the label on the pump, not the colour.
- The first fill in a new motor is the time to check the filler flap — inside it, or on the cap, plenty of vehicles state which fuel they take.
- Mark your key. In a house with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of intending to remember.
- Before the nozzle comes off the pump the first time you fuel a hired or new vehicle, say "diesel" out loud. Silly, perhaps, yet it does the trick.
- Tuck your phone away. This is an easy mistake to make while you are thinking about something else.
- Some diesels have a filler built to refuse a petrol nozzle, and devices you can add are available for vehicles without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop reading the petrol pump.
- Noticing it halfway? Stop there and then. A weaker mix results from less petrol in the tank, yet the next stage stays the same: don't crank it.
Trevithal: already put petrol in a diesel?
The order of things is brief, then. Leave it unstarted, with the ignition off as well. The attendants at the forecourt — whether at Texaco itself or wherever you filled up — will normally help push it away from the pump if you ask. Next, 0333 366 0103. We'll ask what went in, about how much, and if it's been run.
If it was AdBlue and not petrol, say so. That's a separate fault — corrosion and deposits and not lost protection — and it has its own page for Trevithal.
What makes one Trevithal petrol in a diesel job cost more than the next
An honest single price doesn't exist here: four situations, four separate tasks. Which of them you are in is mostly what moves the cost. Two things follow that: the petrol that got in as a share of what your tank takes, then the spot the car is in and whether a van can reach it safely.
Before any quote, not after, we ask three queries: the fuel that was put in, the volume, and whether it's run. That is why. A range becomes a straight figure when the replies are in.
About Trevithal
Trevithal is a coastal locality in Cornwall, situated approximately 25 miles from Truro and 256 miles from London, with a population of around 555 people. Trevithal sits at an elevation of 80 metres, overlooking the surrounding coastline. Trevithal is characterised by its predominantly detached housing stock, reflecting its residential nature. Trevithal is close to nearby places such as Mousehole and Paul, and is part of the wider Cornwall landscape.
Fuel drain cover across Cornwall, Trevithal included
Petrol in diesel calls in Trevithal — part of the TR postcode area — go to vans that likewise cover the places about it, Mousehole, Paul and Sheffield among them. The car does not need to move to us: our technicians drain on a forecourt, in a supermarket car park, in a lay-by or on your own drive.
At the petrol pump in Trevithal, still?
Then you are in the best position there can be. Ring, and leave it turned off.