How Worried Should You Be? Petrol in a Diesel Car in Gauldry
Not started? Then less anxious than you likely are. "Have I wrecked it?" is the first thing everyone in Gauldry asks, and the honest answer is normally no, since petrol resting in a diesel tank harms nothing until it is drawn through the fuel system — by ignition priming, by your starter, or by being driven. Petrol in Diesel is who to call, with the motor kept off, so it remains that way. Below, this page sets out what petrol really does inside a diesel, how far it might have gone, and how to stop it happening to you again.
Petrol in a diesel: what does it do to the motor?
On its way through a motor, diesel has two jobs. Before it burns, it protects — and then it ignites. Designed to extremely fine gaps, the fuel injectors and the pump rely on the diesel moving through them to stop their surfaces wearing against one another.
Poorly at the first, not at all at the second: that is petrol. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump running on the mixture wearing itself. It's also made to resist igniting under compression — the opposite of what a diesel needs — which is why you get the knocking.
Seen together, they show what shape the problem takes. Not contact but movement is what causes the damage. All a tank with petrol in it amounts to is a fuel issue. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with the fuel to your injectors further on.
Four scenarios we see in Gauldry: how bad is petrol in a diesel?
Filled up, not once started. The best case there can be. On a forecourt, and genuinely only there, that petrol is still confined to that tank — since anywhere else the car was driven to get to it. The job is emptying and purging on the spot.
Ignition on, or started for a moment. Once primed, your system has drawn petrol out of your tank as far as your filter and the lines. Still normally easy: drain, flush, and the fuel filter seen to.
Some miles driven, and your pump has spent each of them running on diluted fuel. The work is your tank, the lines, the filter and fresh fuel through the whole system, and how hard your car was driven counts as much as how far. Short trips, like the school run to the local primary school, are one matter. Very different again: a run to Dundee, under 5 miles away, or any distance on the M90, under 15 miles from Gauldry, where your engine kept labouring hard.
Driven until it protested. Clattering, a ragged idle, smoke, a throttle that has gone soft. What you are hearing is your motor signalling fuel that no longer runs like diesel. Leave it where it stops: a lay-by, a side street, the verge on Quality Street. A vehicle pulled over quickly very seldom has permanent damage, because the fuel drain and the flush, which still go first, take care of it.
Gauldry motorists and the petrol in a diesel myths they hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. Nothing comes out when you top up — that tank just holds more of the same blend. Percentage is not how a diesel fuel system tolerates petrol, whatever that advice supposes.
"Current diesels can handle a little petrol" — a myth, and closer to the opposite. A modern diesel sends its fuel through smaller parts at higher pressure, which makes the lubrication count more, not less.
This is the one that catches people. Myth: "If it starts and drives, there's no harm done." Diesel in a petrol motor normally means a motor that will not run: the driver stops, and so does the harm. A diesel fed petrol normally starts, idles and drives away as if nothing has happened, while the pump wears. Fine and running are not the same thing.
Myth: "Add some two-stroke oil and drive it home." It's an old fix for a distinct issue. What petrol has weakened remains thinned, and that petrol stays inside your tank regardless.
Myth: "Drain your tank yourself and you are sorted." After your engine has run, some of the petrol is no longer in that tank: it's in the fuel filter and your lines, and it goes right back through your pump on your next start. And, a can of petrol filled by the roadside is genuinely dangerous.
Why petrol in a diesel occurs at all
It is rarely carelessness, and nobody does it on purpose. The petrol nozzle is the slimmer of the two and slides into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol motor at all. The forecourt makes it easy, and the error runs one way.
It occurs when habit and your car stop matching. Courtesy car, hire car, or a vehicle that's new. One petrol and one diesel on the driveway of the same household. A well-known forecourt with the pumps in a different order. A train to catch, and a rushed fill on the way to Dundee. Exactly the moment it happens: after years of driving petrol, a driver fills a diesel Volkswagen Golf for the first time. Your hand does what it has always done once you add rain, a phone call or a back seat full of children.
Next time you fill up in Gauldry: preventing petrol in a diesel
- A green handle for unleaded and black for diesel is normal in the UK — but not on every forecourt. Trust the label on the pump, not the colour.
- The first fill in an unfamiliar vehicle is the time to check your filler flap — on it, or on the cap, plenty of cars state the fuel to use.
- A coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember, for a household with one of each.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the petrol pump. It seems daft and it does the trick.
- Thinking about something else is when this becomes an easy mistake to make, and so tuck the phone away and keep your mind on the petrol pump.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to refuse a petrol nozzle, and aftermarket devices exist for the rest. Count it as a safety net, then keep reading the petrol pump.
- Spotting it mid-fill? Stop at once. A thinner mixture results from less petrol inside your tank, but your next stage stays the same: don't crank it.
Petrol already in a diesel in Gauldry? Begin here
In that case, there is only a short order of things. Starting it is out, and so is switching on the ignition. The attendants on the forecourt — whether at Shell itself or wherever you filled up — will normally help roll it away from the pump if you ask. Phone 0333 366 0103 next, with three facts — your fuel, the approximate amount, and whether it's run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost lubrication, make it a separate issue — Gauldry has a page just for it.
Gauldry petrol in a diesel jobs: why one costs more than another
The four situations above are four different tasks, so no single price for this would be honest. What moves your cost is chiefly which of them you're in. Where the car is matters too, and whether a technician can safely reach it, after the share of petrol to what that tank takes.
That is why we ask three questions before pricing rather than after: what was put in, how much, and if it's run. Given the answers, there is a straight figure instead of a range.
About Gauldry itself
Gauldry is a small village in Fife, situated on the coast near Dundee, with a mix of detached housing and scenic views. Gauldry sits at an elevation of 106 metres, looking out over the surrounding countryside and the sea. Gauldry is close to other nearby places such as Bottomcraig, Fincraigs, and Kirkton, and is within commuting distance of Dundee. Gauldry has a population of around 640 people, living in predominantly detached homes.
Fuel drain cover across Fife, Gauldry included
Bottomcraig, Fincraigs and Kirkton are among the locations around Gauldry that the same teams work, answering petrol in diesel calls across Gauldry's DD postcode area. A forecourt, a supermarket car park, a lay-by or your own drive are all spots we drain, and your vehicle doesn't need to move to us.
At the pump around Gauldry, right now?
Nothing beats it: that's where you now are. Turned off it stays; then call.