How Worried Should You Be? Petrol in a Diesel Car in St Dympnas
Not started? Then less worried than you probably are. Till your ignition primes your pump, the starter turns, or your car is driven, petrol in a diesel tank simply rests there and does nothing. Which means the truthful reply to that first St Dympnas query — "have I ruined it?" — usually no. Petrol in Diesel is who to ring, with the motor kept off, so it remains that way. The remainder of this page covers 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.
The engine and petrol in a diesel: what happens
Two jobs fall to diesel on its route through a motor. It combusts, and before it burns it protects. The high-pressure fuel pump and your injectors are designed to very fine gaps, and the diesel passing through them is what keeps those surfaces from wearing against one another.
The second task petrol does not do at all, and the first it does poorly. It's thinner than diesel and takes away the protection the system rests on, so a pump running on a petrol blend is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That's where the clattering comes from.
Put these together and the shape of the problem is plain. Not contact but circulation is what does the damage. All a tank with petrol in it amounts to is a fuel fault. After the pump has been labouring on that petrol, a mechanical problem has begun: anything shed by a pump that is wearing down travels onward to the fuel injectors with the fuel.
Four situations we see in St Dympnas: how serious is petrol in a diesel?
The best case there can be: filled up, not once started. The petrol is inside your tank and just the tank, and the task is a drain and a flush where the car sits. This is the one scenario that can only really occur at a forecourt, since anywhere else the vehicle has been driven to get there.
The ignition switched on, or a brief start. The fuel system has been bled, and so petrol has left your tank and reached the fuel filter and your lines. That's normally still an easy task — a drain, a flush, and your filter seen to.
Driven a couple of miles. Now your pump has spent these miles labouring on diluted fuel. The work is your tank, the lines, your filter and clean fuel through the entire system, and how hard the vehicle was driven matters as much as how far. Driving the children to Seaton Primary School is one sort of trip. A run as far as Exeter, under 25 miles away, is a very different task. So is any mileage on the M5, under 25 miles from St Dympnas, where the motor has been working hard throughout.
Driven till it complained. Clattering, a lumpy idle, smoke, a throttle that has gone soft. The fuel is not behaving like diesel any more, and the motor is saying so. Pull up on the spot — on the verge on Boundary Park, at the kerb, down a side road — and don't move it again. What goes first is still the fuel drain and flush, and that sorts it out, with lasting damage very rare if a vehicle is stopped quickly.
St Dympnas people and the petrol in a diesel stories they hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. Nothing is removed by topping up — you're left with a bigger tank, still the same mixture. The idea behind that advice — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: a current diesel copes with a bit of petrol. Rather, the reverse. More precise parts and higher pressure are the way a current diesel runs its fuel, and that makes the protection matter more, not less.
"It starts, it drives, and so there is no harm" — the myth that catches most people than any other. Diesel in a petrol motor generally means a motor that will not run: the driver stops, and so does the damage. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile your pump grinds. Fine and running aren't the same thing.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a distinct fault. The petrol is still inside that tank after that, and whatever it has diluted isn't put back.
"Drain it yourself and you're sorted" — a myth, since after it's been running some petrol lies in the fuel filter and lines, waiting to go straight back through your pump at the next start. And, a can of petrol drained at the roadside is truly hazardous.
How it happens: petrol in a diesel
No one does it on purpose, and it is rarely carelessness. The petrol nozzle is the slimmer of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol car at all. The forecourt makes it easy, and the error runs one way.
It takes place when habit and your car stop matching. A new vehicle, a hire car or a courtesy car. Households running one of each, petrol and diesel. Your usual forecourt, its pumps suddenly in a different order. A train to catch, and a hurried fill on the way to Axminster. Years of petrol vehicles behind you, a diesel BMW 3 Series in front of you on the forecourt for its first tank — that is when. With rain, a call coming in, or children to deal with, the hand simply does what it always has.
Preventing petrol in a diesel next time you fill up around St Dympnas
- Not every forecourt in the UK follows green for unleaded and black for diesel, even if most generally do. Read the pump's label; the colour is just a clue.
- In a car you don't know, look inside the flap over the filler or at the cap before the first fill: plenty of cars state the fuel type there.
- Good intentions count for less than a sticker or a fob in a vivid colour on the diesel's key if a household has one of each. So label it.
- It seems daft and it works: on your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the petrol pump.
- Thinking about something else is when this becomes an easy mistake to make, so put your phone away and keep your mind on the petrol pump.
- Some diesels come with a filler built to refuse a petrol nozzle, and devices you can add exist for vehicles without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop reading the pump.
- The moment you notice, stop: less petrol in your tank makes a weaker mixture. What to do next doesn't change, though — still do not fire it up.
Petrol already in a diesel around St Dympnas? Begin here
Short and simple, then, is the order of things. Don't crank it, and do not switch the ignition on. If you are still at the forecourt — Tower Services or anywhere else — ask the staff to help you roll it clear of the petrol pump. Then phone 0333 366 0103 and tell us what went in, about how much, and if it has run.
If it was AdBlue rather than petrol, say so. That's a separate problem — corrosion and deposits and not lost lubrication — and it has its own page for St Dympnas.
What makes one St Dympnas petrol in a diesel task cost more than the next
There's no fair single price for this, because the four situations above are four separate jobs. Mostly, your cost moves with which situation you are in. Where the car is counts too, and whether our van can safely get to it, after the ratio of petrol to what the tank takes.
What went in, how much, and if it's run — three questions we ask before costing, not after, for precisely that reason. With the answers, there is a straight figure instead of a range.
About St Dympnas
St Dympnas is a coastal locality in Devon, situated near the towns of Seaton and Colyford, with a mix of detached housing and scenic views. St Dympnas sits at a low elevation of 19 metres, close to the sea and within a short drive of the city of Exeter. St Dympnas has a population of around 2038 people, living in a predominantly detached housing stock. St Dympnas is part of the wider South West region, with London approximately 139 miles to the east.
Fuel drain cover across Devon, St Dympnas included
Petrol in diesel calls in St Dympnas — part of the EX postcode area — go to teams that also cover the places around it, Colyford, Seaton and Holyford among them. A forecourt, a supermarket car park, a lay-by or your own drive are all places our engineers work, and your car does not need to move to us.
In St Dympnas and still at the petrol pump?
No position is better: that's where you now are. Switched off it remains; then call.