How Worried Should You Be? Petrol in a Diesel Car in Tresillian
Probably less than you are now — as long as no one has started the car. Everyone around Tresillian starts with "have I wrecked it?", and the honest answer is usually no: petrol left inside the tank of any diesel remains harmless until priming, cranking or driving draws it into the system. Leave your motor off then ring Petrol in Diesel — that keeps it that way. The rest of this page sets out what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it does not happen to you again.
What petrol in a diesel does to your engine
On its way through an engine, diesel has two tasks. It lubricates first, and after that does it burn. Your high-pressure pump and your injectors are made to very fine clearances, and your diesel passing through them is what stops those surfaces from wearing against one another.
Poorly at the first, not at all at the second: that's petrol. Being less viscous than diesel, petrol strips out the protection a fuel system needs, leaving a pump on that mixture to wear itself. It's also made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the rattling.
Together, those make the shape of the issue clear. It is circulation that does the damage, not contact. Petrol in a tank is a fuel problem. A pump that has been running on that petrol is the start of a mechanical one, and whatever a worn pump sheds travels on with the fuel to your injectors downstream.
Tresillian, petrol in a diesel: four situations, from mild to major
Filled up, not once started. The best case there is. That petrol is inside the tank and just the tank, and the job is a drain and a flush where your car stands. This is the one scenario that can only really happen on a forecourt, because anywhere else the car has been driven to get there.
Ignition on, or started for a second. With your system primed, the lines and filter already contain petrol that came from your tank. Still usually simple: drain, flush, and the filter sorted.
The pump now worked a few miles on thinned fuel — that's what driving the car does. The work is the tank, your lines, your filter and fresh fuel through the entire circuit, and how hard the car was driven counts as much as how far. The school run to Tregolls Academy is one thing. Any mileage on the M5, over 50 miles from Tresillian, means your engine working hard throughout, and a run to Truro, under 3 miles away, makes a very different job too.
Driven until it protested. Clattering, an uneven idle, smoke, a throttle that has gone soft. The motor is telling you the fuel is no longer behaving like diesel. Pull up on the spot — on the verge on Polsue Way, at the kerb, down a side road — and don't move it. Long-term damage is very rare when a vehicle is stopped early, and the fuel drain and flush-through that still go first deal with it.
What Tresillian people get told about petrol in a diesel — and the myths in it
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing comes out when you top up — the tank just carries more of the same mixture. That guidance assumes a diesel fuel system tolerates petrol by percentage. It does not.
"Current diesels can handle a little petrol" — a myth, and closer to the reverse. Lubrication matters more on current diesels, not less, because their fuel passes through more precise components at higher pressure.
The myth that catches motorists off guard: if it starts and drives, it must be unharmed. A petrol engine fed diesel normally will not run, and so the driver stops and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually will; meanwhile the pump wears. Fine and running aren't the same at all.
Myth: "Add some two-stroke oil and drive the car home." It's an outdated fix for a separate problem. It does not put back what petrol has diluted, and the petrol is still inside your tank later.
"Drain it yourself and you are sorted" — a myth, since after it has been running some petrol lies in your filter and lines, ready to go right back through the pump on your next start. Draining petrol into a can at the kerbside is also really risky.
Petrol in a diesel: how does it happen?
It's seldom carelessness, and nobody does it on purpose. 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.
When habit and your car stop matching, it happens. A new vehicle, a hire car or a courtesy car. Households running one of each, petrol and diesel. Your normal forecourt, its pumps suddenly in a different order. A hurried fill on the way to Truro with a train to catch. 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 children to deal with, your hand simply does what it always has.
How to prevent petrol in a diesel at your next fill-up in Tresillian
- The label is what counts, and so check the petrol pump rather than the colour: in the UK unleaded handles are normally green and diesel black, yet not on each forecourt.
- The first fill in a new car is the time to check the filler flap — inside it, or on the cap, many vehicles state which fuel to use.
- One of each in the house? Label your key to the diesel — a coloured fob, a sticker — because meaning to remember isn't enough.
- "Diesel", aloud, before you pick up the nozzle — each time a new or hired car needs its first tank. It seems daft. It works.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck your phone away.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to reject a petrol nozzle, and add-on devices are available for the rest. Treat it as a backstop, and keep checking the petrol pump.
- As soon as you notice, stop: less petrol in that tank means a weaker mix. What to do next doesn't change, though — still don't crank it.
Put petrol in a diesel around Tresillian already?
Short and simple, then, is the order of things. Never start it, and don't switch your ignition on. Ask the staff to help you push it clear of the pump if you are still on the forecourt, whether that's Texaco or anywhere else. Then phone 0333 366 0103 and tell us what got in, roughly how much, and if it's run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a separate problem — Tresillian has a page all for it.
Tresillian petrol in a diesel tasks: why one costs more than another
There's no honest single quote for this, since the four situations above are four different tasks. The situation itself does most of the work of moving the cost. Two things follow that: the petrol that went in as a share of what the tank holds, then the place the vehicle is in and whether a van can reach it safely.
Ahead of any quote, not after, we ask three questions: the fuel that was put in, the amount, and whether it's run. That's why. Given those replies, there is a straight figure instead of a range.
About Tresillian, for a moment
Tresillian is a small village in Cornwall, situated on the banks of the River Fal, near the city of Truro. Tresillian has a low elevation of around 7 metres above sea level and is surrounded by nearby places such as Merther, St Clement, and Tresawle. Tresillian is characterised by its predominantly detached housing stock, reflecting its rural setting. Tresillian is located approximately 228.6 miles west of London, in the South West region of England.
Fuel drain cover in Tresillian and across Cornwall
Tresillian waits in the TR postcode area, and the vans that answer petrol in diesel jobs there work the places around it as well — Merther, St Clement and Tresawle among them. We drain wherever your car is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
Still at the pump in Tresillian?
No position is better: that's where you are. Switched off it stays; then call.