Should You Worry? Petrol in a Diesel Car in Water
Unstarted? Then less anxious than you likely feel. Till your ignition primes your pump, the starter turns, or your vehicle is driven, petrol in a diesel tank just sits there and does no harm. Which makes the honest reply to that first Water question — "have I ruined it?" — usually no. To leave the vehicle like that, phone Petrol in Diesel and leave the engine alone. The remainder of this page covers what petrol really does to a diesel, how to judge how far it has got, and how to make sure it does not happen to you a second time.
What petrol in a diesel does to the motor
On its way through a motor, diesel does two jobs. Oiling comes before burning; it does both. Very fine tolerances are built into the injectors and the high-pressure fuel pump, and only your diesel running through stops those surfaces grinding together.
The second job petrol does not do at all, and the first it does poorly. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, so a pump on that mixture wearing itself. It's equally made to resist igniting under compression — the reverse of what a diesel needs — which is why you hear the rattling.
The shape of the issue is clear once you put those together. Not contact but movement is what causes the damage. Where the petrol is only in that tank, it's a fault of fuel, nothing more. Whatever a worn pump sheds goes on, carried by the fuel, into the injectors further along, which is why a pump that has been working on the petrol is where a mechanical issue starts.
Four scenarios we see around Water: how serious is petrol in a diesel?
Fuelled up, not once started. The best case there is. The petrol is in your tank and just the tank, and the job is a drain and a flush where the car stands. This is the one situation that can only really happen at a forecourt, because anywhere else the car has been driven to get there.
A moment's running, or merely the ignition on. Petrol has left that tank and got to your filter and your lines, since your system has been primed. Still usually straightforward: drain, flush, and the fuel filter sorted.
A couple of miles driven, and your pump has spent every one of them working on diluted fuel. The work is that tank, the lines, your filter and clean fuel through the whole circuit, and how hard the vehicle was driven matters as much as how far. Driving the kids to Water Primary School is one sort of trip. Getting as far as Manchester, under 25 miles away, makes a very different task — as does any mileage on the M65, under 5 miles from Water, with the engine working hard all the way.
Driven on till it protested — knocking, smoke, a lumpy idle, a soft throttle. That's your engine telling you its fuel has stopped acting like diesel. Pull up where you are — on the verge on Dean Lane, at the kerb, down a side road — and do not move it. Long-term damage is very unusual when a car is stopped early, and the fuel drain and flush-through that still come first take care of it.
Water motorists and that 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 won't. Nothing is removed by topping up — you are left with a fuller tank, still the same mix. Percentage isn't how a diesel fuel system tolerates petrol, whatever that advice assumes.
If anything, the opposite is true. Myth: "A current diesel can cope with a bit of petrol." Protection counts more on modern diesels, not less, because their fuel runs through more precise components at higher pressure.
One myth that catches people out: if it starts and drives, it must be unharmed. Diesel in a petrol motor normally leaves a motor that won't run: the driver stops, and so does the damage. Whilst your pump wears, a diesel fed petrol normally starts, idles and drives away as though nothing has happened. Running isn't the same as fine.
An old fix for a separate fault is behind this one. Myth: "Add some two-stroke oil and drive the car home." That petrol is still in the tank after that, and what it has weakened isn't put back.
If the motor has been run, part of the petrol sits in your filter and your lines, not that tank — and your next start sends it right back through the pump. So the myth "drain the tank yourself and you're sorted" doesn't stand up. And, a can of petrol drained by the kerbside is genuinely hazardous.
How does petrol in a diesel occur?
On purpose? Never. Through carelessness? Seldom, if ever. The forecourt makes it simple: the petrol nozzle is the slimmer of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle mostly won't go into a petrol motor at all. So the mistake runs one way.
It occurs when habit and the vehicle stop matching. Courtesy car, hire car, or a motor that is new. Two cars on one driveway, one petrol, one diesel. The pumps in a different order on a well-known forecourt. Fuelling up in a hurry en route to Burnley Manchester Road, with a train to catch. Years of petrol vehicles behind you, a diesel Peugeot 308 in front of you at the forecourt for its first tank — that's when. Throw in a back seat full of children, a phone call or rain, and habit wins.
Next time you fill up in Water: avoiding petrol in a diesel
- The label is what counts, and so check the pump instead of the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt.
- In a vehicle you don't know, look inside the flap over your filler or at the cap before your first fill: plenty of vehicles print the fuel there.
- Good intentions count for less than a sticker or a fob in a bright colour on the diesel's key if a home has one of each. So mark it.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the pump. It seems daft and it does the trick.
- Mistakes like this are straightforward to make while your mind is on something else, and so your phone goes away.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler designed to block a petrol nozzle, and add-on devices are available for the remainder. Count it as a backstop, then keep reading the petrol pump.
- Less petrol means a weaker blend, and so stop the moment you realise — while remembering that the next step is unchanged. It's still not to start it.
Put petrol in a diesel around Water already?
Short and simple, then, is the order of things. Starting it is out, and so is switching on the ignition. If you are still at the forecourt — Shell or anywhere else — ask the attendants to help you roll the vehicle clear of the petrol pump. Ring 0333 366 0103 next, with three answers — your fuel, the rough amount, and if it has run.
If it was AdBlue instead of petrol, say so. That is a different issue — corrosion and deposits and not lost protection — and it has its own page for Water.
One petrol in a diesel task around Water costs more than another. Why?
Four separate tasks lie behind the four scenarios above — which is why there's no fair single quote. Chiefly, the cost shifts with which one you're in. Beyond that it's the ratio — how much petrol was put in against how much the tank holds — and then where the vehicle is and whether a van can reach it safely.
What got in, how much, and whether it has run — three questions we ask before quoting, not after, for precisely that reason. A range turns into a straight figure once those replies are in.
About Water and where it is
Water is a small village in Lancashire, situated on the riverside in the North West of England. Water sits at an elevation of 266 metres, with nearby settlements including Forest Holme, Bank Top, and Lumb. Water has a population of around 633 people, predominantly living in terraced housing. Water is located 17.2 miles from Manchester and 177.2 miles from London.
Fuel drain cover in Water and across Lancashire
Forest Holme, Bank Top and Lumb are among the places near Water that the same vans work, answering petrol in diesel call-outs across Water's BB postcode area. You need not bring your vehicle to us. Forecourts, supermarket car parks, lay-bys and your own drive are all places we drain.
Water: still at the petrol pump?
Then, you could not be in a better spot. Keep it off. Call.