Gwills: Petrol in a Diesel Car? How Worried to Be
Not started? Then less anxious than you likely are. Everyone in Gwills begins with "have I ruined it?", and the fair answer is usually no: petrol left in your tank of a diesel remains harmless till priming, cranking or driving draws it into your fuel system. Petrol in Diesel is who to phone, with your engine left off, and so it remains that way. Further down, this page sets out what petrol actually does inside a diesel, how far it might have got, and how to stop it happening to you a second time.
Your engine and petrol in a diesel: what goes on
Passing through a motor, diesel does two things at once. It burns, and before it ignites it lubricates. What stops the surfaces inside the high-pressure pump and the fuel injectors from wearing against each other is the diesel flowing through them — they're designed to extremely fine tolerances.
Badly at the first, not at all at the second: that is petrol. A pump working on a petrol blend is wearing itself out, since petrol is thinner than diesel and strips out the protection your fuel system depends on. Petrol is also designed to resist igniting under compression — the reverse of what a diesel needs from its fuel — and that's where the clattering comes.
The shape of the trouble is plain when you put those together. Not contact but circulation is what causes the damage. Any tank with petrol in it is a fuel fault. A pump that has been working on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with your fuel to the injectors further on.
How bad is petrol in a diesel? Four situations our technicians see in Gwills
Filled up, and never started: nothing beats it. Only that tank has petrol in it, so the task is clearing the tank and purging the system where the vehicle sits. This scenario can only truly happen on a forecourt: anywhere else, the vehicle got there by being driven.
Ignition on, or started for a moment. The system has been bled, so petrol has left the tank and reached the filter and your lines. That's usually still an easy job — a drain, a flush, and your filter seen to.
Those few miles on the road were your pump working on fuel diluted by petrol the whole way. How hard the vehicle was driven counts as much as how far, and this work covers that tank, the fuel lines, the fuel filter and clean fuel through the whole circuit. On the school run to The Bishops CofE Learning Academy, the miles is short. A run as far as Truro, under 10 miles away, is a very different job. So is any mileage on the M5, over 50 miles from Gwills, where the engine has been running hard throughout.
Clattering, an uneven idle, smoke, a throttle gone soft: driven until it complained. That is the motor telling you its fuel has stopped acting like diesel. Stop where you are — on the verge on Stret Avalennek, at the kerb, down a side road — and do not move it again. A car stopped soon very seldom has lasting damage, since the fuel drain and the flush-through, which still go first, sort it out.
Gwills people and the petrol in a diesel myths they hear
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." A bigger tank of the same mixture is all it gives, because topping up removes nothing. The idea behind that guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: a current diesel copes with a bit of petrol. Rather, the reverse. Finer parts and higher pressure are how a newer diesel runs its fuel, and that makes the protection count more, not less.
"It starts, it drives, and so no harm done" — the myth that trips up most people than any other. Feed diesel to a petrol motor and it generally won't run, and so the driver stops — and the damage stops with them. A diesel fed petrol generally starts, ticks over and drives away as if nothing has happened, while the pump grinds. Running doesn't mean fine.
An old fix for a distinct problem is behind this one. Myth: "Add some two-stroke oil and drive the car home." The petrol is still in the tank after that, and what it has diluted isn't put back.
"Drain it yourself and you are sorted" — a myth, because after it's been running some petrol lies in the fuel filter and lines, ready to go right back through the pump on your next start. It's also truly risky to drain petrol into a can by the kerbside.
Petrol in a diesel: how does it happen?
Nobody does it on purpose, and it's rarely carelessness. The forecourt makes it simple: the petrol nozzle is the narrower of the two, and it slips into a diesel filler with almost no resistance, whilst a diesel nozzle generally will not go into a petrol vehicle at all. So the slip runs one way.
Routine and the vehicle falling out of step is how it occurs. Any vehicle that is new to you — a hire car, on loan as a courtesy car, or just bought. Two motors on one driveway, one petrol, one diesel. Your normal forecourt, its pumps now in a different order. A train to catch, and a rushed fill on the way to Quintrell Downs. Precisely the moment it happens: after years of driving petrol, a driver fills a diesel Volkswagen Passat for the first time. Your hand does what it has always done when you add rain, a phone call or a back seat full of children.
Gwills people: how to prevent petrol in a diesel next time
- The label is what counts, so read the pump instead of the colour: in the UK unleaded handles are usually green and diesel black, but not on each forecourt.
- The first fill in an unfamiliar car is the time to check the filler flap — inside it, or on the cap, plenty of cars state the fuel to use.
- Good intentions do less than a sticker or a fob in a vivid colour on your diesel's key if a house has one of each. So label it.
- "Diesel", aloud, before you pick up the nozzle — each time a new or hired car needs its first tank. It seems silly. It works.
- Mistakes like this are simple to make whilst your mind is on something else, so the phone goes away.
- Some diesels have a filler designed to reject 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 pump.
- Spotting it halfway? Stop at once. A thinner mixture follows from less petrol inside that tank, yet the next step stays the same: do not fire it up.
Put petrol in a diesel around Gwills already?
Short and simple, then, is the order of things. Leave it unstarted, with your ignition switched off too. Yet on the forecourt, at Morrisons or anywhere else? Ask the attendants to help you push it clear of the petrol pump. Next, 0333 366 0103. We'll ask what was put in, about how much, and if it's been run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost protection, make it a different issue — Gwills has a page just for it.
One petrol in a diesel job around Gwills costs more than another. Why?
There's no honest single price for this, because the four situations above are four different tasks. What moves your cost is mostly which of them you are in. Two things follow that: the petrol that was put in as a share of what that tank holds, then the place the car is in and whether a van can get to it safely.
What went in, how much, and whether it has run — three queries we ask before costing, not after, for precisely that reason. The answers change a range into a straight figure.
About Gwills itself
Gwills is a small coastal locality in Cornwall, situated near the city of Truro and close to the nearby places of Lane, Trencreek, and Trevemper. Gwills has a population of around 606 people and is characterized by predominantly terraced housing. Gwills is located at a low elevation of 7 metres above sea level, reflecting its coastal setting.
Fuel drain cover around Gwills and across Cornwall
Petrol in diesel calls around Gwills — part of the TR postcode area — go to teams that also cover the locations about it, Lane, Trencreek and Trevemper included. Our technicians drain wherever the vehicle 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 petrol pump in Gwills?
Then you are in the best spot there is. Ring, and keep it switched off.