Petrol in a Diesel Car in Oban: How Worried Should You Be?
Unstarted? Then less anxious than you likely feel. Until the ignition primes your pump, your starter cranks, or your vehicle is driven, petrol in a diesel tank simply waits there and does nothing. Which means the honest reply to that first Oban query — "have I ruined it?" — normally no. Petrol in Diesel is who to call, with your engine kept off, and so it remains 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 doesn't happen to you again.
Petrol in a diesel: what does it do to the engine?
Diesel does two jobs on its way through an engine. It burns, and before it ignites it protects. Built to extremely fine tolerances, your injectors and your pump depend on your diesel flowing through them to keep their surfaces from wearing against one another.
Of those two jobs, petrol handles the first badly and the second not at all. The knocking comes from petrol being designed not to ignite when compressed, which is precisely the opposite of what a diesel needs. On top of that it is thinner than diesel, it strips away the protection the system depends on, and any pump working on that blend is wearing itself.
Combined, those make the shape of the issue clear. Not contact but circulation is what does the harm. Where the petrol is only in the tank, it's a fault of fuel, nothing more. Whatever a worn pump sheds goes on, carried by your fuel, into the injectors downstream, which is why a pump that has been working on the petrol is where a mechanical issue begins.
Oban, petrol in a diesel: four situations, from mild to significant
Filled but not once started — as good as it gets. That petrol is inside that tank and just that tank, and the task is a drain and a flush where your car stands. This is the one scenario that can only truly occur on a forecourt, since anywhere else the vehicle has been driven to get there.
Started for a second, or only your ignition on. Petrol has come out of that tank and reached your filter and the fuel lines, because your system has been primed. Drain, flush, deal with the fuel filter: still normally easy.
Your pump now worked a few miles on diluted fuel — that's what driving the vehicle meant. Distance is only half of that; how hard it was driven counts equally. Either way this work runs to the tank, the fuel lines, the fuel filter and clean fuel through the entire system. Driving the kids to the local primary school is one kind of trip. Very different again: a run to Glasgow, over 50 miles away, or some miles on the M8, under 50 miles from Oban, where the motor never stopped working hard.
Driven till it complained. Knocking, an uneven idle, smoke, a throttle that has gone soft. That's your engine telling you its fuel no longer is acting like diesel. Leave it where it stops: a lay-by, a quiet street, the verge on Argyll Square. A vehicle pulled over early very rarely has long-term damage, because the drain and the flush, which still go first, take care of it.
What Oban motorists get told about petrol in a diesel — and the stories in it
False: topping up to full with diesel makes it fine. It does not. Nothing is removed when you top up — your tank just holds more of the same mixture. That advice presumes a diesel fuel system handles petrol by percentage. It doesn't.
"Current diesels can handle a little petrol" — a myth, and closer to the opposite. Finer components and higher pressure are how a newer diesel runs its fuel, and that makes the protection count more, not less.
Myth: "If it starts and drives, there's no harm done." This is the one that catches motorists. A petrol motor fed diesel generally won't run, and so the driver stops and the harm stops with them. Feed petrol to a diesel and it usually starts, idles and pulls away like nothing has happened — all the while its pump is wearing. Fine and running are not the same thing.
An old fix for a distinct issue is behind this one. Myth: "Add some two-stroke oil and drive the car home." What petrol has diluted remains diluted, and that petrol remains inside the tank anyway.
"Drain it yourself and you're sorted" — a myth, because after it has been running some petrol sits in the fuel filter and lines, waiting to go straight back through the pump on the next start. Emptying petrol into a can by the kerbside is also really hazardous.
How it happens: petrol in a diesel
Carelessness is seldom the cause, and nobody means to do it. One way only, since of the nozzles: the slimmer petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one mostly will not fit a petrol vehicle. That is how the forecourt makes it straightforward.
It happens when routine and the car stop matching. A new motor, a hire car or a courtesy car. One petrol and one diesel on the driveway of the same household. A well-known forecourt with the pumps in a different order. A rushed fill en route to the nearest station with a train to catch. A new-to-you diesel Renault Megane, its first fuelling, and a driver accustomed to petrol: exactly when it occurs. With rain, a call coming in, or children to deal with, your hand simply does what it always has.
Next time you fill up in Oban: avoiding petrol in a diesel
- The label is what matters, and so check the pump rather than the colour: in the UK unleaded handles are normally green and diesel black, but not on every forecourt.
- The first fill in a new car is the time to check the filler flap — on it, or on the cap, many vehicles state the fuel they take.
- Good intentions count for less than a sticker or a fob in a vivid colour on the diesel's key if a house has one of each. So mark it.
- Before the nozzle comes off the petrol pump the first time you fuel a hired or new car, say "diesel" out loud. Silly, perhaps, yet it works.
- Thinking about something else is when this becomes an easy mistake to make, and so put the phone away then keep your mind on the pump.
- Some diesels have a filler designed to refuse a petrol nozzle, and devices you can add exist for motors without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the pump.
- Stop the moment you realise. Less petrol inside the tank makes a weaker mixture. It doesn't change what to do next, which is still not to fire it up.
Petrol already in a diesel around Oban? Begin here
Then the order of things is brief. Do not fire it up, and do not turn your ignition on. If you are still on the forecourt — Tesco or anywhere else — ask the staff to help you roll the vehicle away from the petrol pump. Ring 0333 366 0103 next, with three answers — the fuel, the approximate quantity, and whether it has run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a different issue — Oban has a page just for it.
What makes one Oban petrol in a diesel task cost more than the next
A fair single price doesn't exist here: four scenarios, four separate jobs. The situation itself does most of the work of moving the cost. Two things follow that: the petrol that went in as a proportion of what the tank holds, then the spot the car is in and whether our van can reach it safely.
Ahead of any quote, not after, we ask three questions: your fuel that went in, the quantity, and if it has run. That's why. Their answers are what turn a range into one firm number.
About Oban itself
Oban is a coastal town in Argyll and Bute, situated on the western coast of Scotland, with Pulpit Hill and Dalintart nearby. Oban sits at an elevation of around 30 metres, looking out over the sea towards the islands. Oban is a significant residential centre, with a population of approximately 7309 people, predominantly living in flats. Oban is located about 60 miles from Glasgow and 402 miles from London, making it a key hub in the region.
Fuel drain cover around Oban and across Argyll and Bute
Pulpit Hill, Dalintart and Soroba are among the places around Oban that the same teams work, answering petrol in diesel jobs across Oban's PA postcode area. The car doesn't need to come to us: our technicians drain at a forecourt, in a supermarket car park, in a lay-by or on your own drive.
Oban: still at the pump?
The best spot there is, then — that's where you are. Switched off it stays; then ring.