How Worried Should You Be? Petrol in a Diesel Car in Little Heath
Less than you likely are, if it hasn't been started. Petrol resting in a diesel tank does nothing to your motor until something pulls it through the fuel system — your ignition priming the pump, the starter, or the drive on its own. So the truthful answer to the first question anyone around Little Heath asks, "have I ruined it?", is normally no. Keep it like that: leave your engine off and ring Petrol in Diesel. Keep reading for three things: the effect petrol has inside a diesel engine, the signs of how far it has spread, and the way to make sure you never do it again.
What petrol in a diesel does to the engine
On its way through an engine, diesel has two jobs. It ignites, and before it combusts it lubricates. What stops the surfaces inside your high-pressure pump and the fuel injectors from wearing against one another is your diesel flowing through them — they are designed to very fine clearances.
Poorly at the first, not at all at the second: that's petrol. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump on the 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 clattering.
Put these together and the shape of the trouble is clear. It's movement that does the damage, not contact. Where that petrol is only in the tank, it's a problem of fuel, nothing more. Whatever a worn pump sheds goes on, carried by the fuel, into the injectors downstream, which is why a pump that has worked on that petrol is where a mechanical fault starts.
Four situations our engineers see around Little Heath: how bad is petrol in a diesel?
Fuelled, and not started: no case is better. On a forecourt, and truly only there, the petrol is still limited to that tank — because everywhere else your car was driven to get to it. The job is emptying and flushing on the spot.
A brief spell of running, or merely your ignition on. With your system primed, the lines and filter now contain petrol that has come from the tank. Drain, flush, see to your filter: still usually straightforward.
A few miles driven, and the pump has spent every one of them labouring on weakened fuel. Distance is only half of that; how hard it was driven counts just as much. Either way the work includes your tank, the lines, the filter and clean fuel through the whole circuit. Driving the kids to St Paul's Catholic Primary School is one kind of trip. Any mileage on the M4, under 3 miles from Little Heath, means the motor has worked hard throughout, and a run to Oxford, under 25 miles away, is a very different task too.
Knocking, an uneven idle, smoke, a throttle gone soft: driven until it complained. That's your motor telling you its fuel no longer is behaving like diesel. Pull up wherever you are — the verge on Hildens Drive, a lay-by, a side street — and leave the car where it is. A vehicle stopped quickly very rarely has lasting damage, since the fuel drain and the flush, which still come first, take care of it.
Petrol in a diesel stories Little Heath people hear
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." A fuller tank of the same mixture is all it gives, because topping up takes out nothing. The assumption behind that advice — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: "A current diesel can cope with a bit of petrol." If anything, the opposite. Protection counts more on current diesels, not less, because their fuel runs through smaller components at higher pressure.
The myth that catches drivers off guard: if it starts and drives, it must be unharmed. Diesel in a petrol motor normally means a motor that will not run: the driver stops, and so does the damage. Whilst the pump grinds, a diesel fed petrol normally starts, idles and drives away as if nothing has happened. Being able to run is not the same as being fine.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an outdated workaround for a different problem. The petrol is still in your tank after that, and whatever it has diluted is not put back.
If the engine has been run, part of the petrol sits in the fuel filter and the fuel lines, not the tank — and your next start pulls it straight back through your pump. So the myth "drain the tank yourself and you are sorted" does not stand up. Also, a can of petrol drained by the roadside is genuinely dangerous.
How it happens: petrol in a diesel
It's rarely carelessness, and no one does it on purpose. The forecourt makes it easy: the petrol nozzle is the narrower 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 vehicle at all. So the error runs one way.
The moment habit stops matching your car is the moment it takes place. Hire cars, courtesy cars, and vehicles that are new to you. A household with one petrol and one diesel on the driveway. A familiar forecourt with the pumps in a different order. A train to catch, and a rushed fill en route to Tilehurst. Years of petrol vehicles behind you, a diesel Volkswagen Golf in front of you on the forecourt for its first tank — that is when. Throw in rain, a phone call or a back seat full of kids, and the hand does what it has always done.
Next time you fill up around Little Heath: preventing petrol in a diesel
- The label is what matters, so check the petrol pump instead of the colour: in the UK unleaded handles are normally green and diesel black, but not on every forecourt.
- Many cars state the fuel type inside the filler flap or on the cap, so check it on your first fill in any car you do not know.
- One of each in the home? Label your key to your diesel — a coloured fob, a sticker — since intending to remember is not enough.
- Before the nozzle leaves the pump the first time you fuel a hired or new motor, say "diesel" out loud. Silly, yes, but it does the trick.
- Put the phone away. This is an easy mistake to make while you are thinking about something else.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to block a petrol nozzle, and add-on devices exist for motors without one. They are a safety net, not a reason to stop checking the pump.
- Stop as soon as you realise. Less petrol in the tank means a thinner mix. It doesn't change what to do next, which is still not to start the car.
Petrol already in a diesel around Little Heath? Begin here
Then the order of things is short. Leave it unstarted, with the ignition off too. Still at the forecourt, at Asda or anywhere else? Ask the attendants to help you push the vehicle away from the pump. Next, 0333 366 0103. We will ask what went in, about how much, and if it's been run.
Say so if it was AdBlue rather than petrol: it's a different fault, with its own page for Little Heath, because AdBlue brings corrosion and deposits rather than lost protection.
What makes one Little Heath petrol in a diesel job cost more than the next
There's no honest single price for this, since the four scenarios above are four different jobs. The scenario itself does most of the work of moving your cost. Two things come after that: the petrol that went in as a proportion of what the tank holds, then the place your car is in and whether a technician can get to it safely.
What got in, how much, and if it has run — three queries we ask before costing, not after, for precisely that reason. A range turns into a straight figure once those answers are in.
About Little Heath and its setting
Little Heath is a suburban area in Berkshire, situated inland at an elevation of 92 metres, and forms part of the larger Reading urban area. Little Heath lies near the villages of Tilehurst and Calcot Row, and is connected to nearby Churchend. Little Heath has a population of approximately 8042 residents, predominantly living in semi-detached housing.
Little Heath and Berkshire: where our fuel drain cover runs
Our vans answering petrol in diesel call-outs in Little Heath, in the RG postcode area, also work the locations near it, Tilehurst, Calcot Row and Churchend among them. The car doesn't need to come to us: we drain on a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Little Heath: still at the petrol pump?
Then you are in the best spot there can be. Turned off it remains; then ring.