How Worried Should You Be? Petrol in a Diesel Car in Threshfield
Likely less than you are now — as long as nobody has started the vehicle. Petrol resting in a diesel tank does nothing to the motor till something draws it through the fuel system — the ignition priming the pump, the starter, or the drive on its own. So the truthful answer to the first question everyone in Threshfield asks, "have I wrecked it?", is usually no. Keep it like that: leave the engine off and call Petrol in Diesel. What petrol actually does to a diesel, how to judge how far it has travelled, and how to keep it from happening again: that is the remainder of this page.
Inside the motor: what petrol in a diesel really does
Passing through a motor, diesel is doing two jobs at the same time. Oiling comes before burning; it does both. What stops the surfaces inside the high-pressure fuel pump and the injectors from grinding against each other is the diesel passing through them — they're designed to extremely fine gaps.
Badly at the first, not at all at the second: that's petrol. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump on that mixture wearing itself. It's also made to resist igniting under compression — the reverse of what a diesel needs — which is where you hear the knocking.
Seen together, they show what shape the issue has. It's movement that causes the harm, not contact. Petrol in a tank is a fuel issue. The beginning of a mechanical problem is a pump that has been working on that petrol — and whatever a worn pump sheds moves on with your fuel to the fuel injectors downstream.
Four scenarios our engineers see in Threshfield: how bad is petrol in a diesel?
Filled but not once started — the best it gets. The petrol is in that tank and only that tank, and the job is a drain and a flush where your car sits. This is the one scenario that can only really happen on a forecourt, since anywhere else the car has been driven to get there.
A moment's running, or just your ignition on. The fuel system has been bled, so petrol has left the tank and got to the filter and your lines. Still generally simple: drain, flush, and the filter seen to.
Your pump has spent a few miles on weakened fuel — that is what driving the car does. The work is that tank, the lines, the fuel filter and clean fuel through the whole circuit, and how hard the car was driven counts as much as how far. The school run to Threshfield Primary School is one matter. Very different once more: a run to Ripon, under 25 miles away, or some mileage on the M65, under 25 miles from Threshfield, where the motor kept labouring hard.
It protested, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone uneven. That's the engine telling you its fuel has stopped acting like diesel. Whether it's the verge on Station Road, a lay-by or a side street, stop where you are then leave it. A car pulled over soon very rarely has permanent damage, since the fuel drain and the flush-through, which still come first, sort it out.
What Threshfield people get told about petrol in a diesel — and the myths in it
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. A bigger tank of the same mixture is all you get, because topping up takes out nothing. A diesel fuel system doesn't accept petrol by percentage in the way that guidance assumes.
"Modern diesels can handle a little petrol" — a myth, and closer to the opposite. A modern diesel runs its fuel through smaller parts at higher pressure, which makes the lubrication count more, not less.
This is the one that catches motorists. Myth: "If it starts and drives, there is no damage done." A petrol engine fed diesel usually will not run, so the driver stops and the harm stops with them. A diesel fed petrol usually starts, idles and drives away as if nothing has happened, whilst the pump wears. 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 different issue. What petrol has weakened stays thinned, and that petrol stays in the tank anyway.
Myth: "Drain that tank yourself and you're sorted." After the motor has run, some of the petrol is no longer in your tank: it is in your filter and the lines, and it goes right back through your pump on the next start. Also, a can of petrol filled at the kerbside is genuinely dangerous.
How it happens: petrol in a diesel
On purpose? Never. Through carelessness? Seldom, if ever. One way only, since of the nozzles: the smaller petrol one slides inside a diesel filler with almost no resistance, whereas the diesel one mostly will not fit a petrol motor. That is how the forecourt makes it easy.
The moment routine stops matching your car is the moment it happens. A motor that is new to you — hired, on loan as a courtesy car, or brand new. A household with one petrol and one diesel on the driveway. A well-known forecourt with the pumps in a different order. Racing for a train at Gargrave and fuelling up en route. A new-to-you diesel Renault Clio, its first fuelling, and a driver accustomed to petrol: exactly when it occurs. Add a back seat full of kids, a phone call or rain, and habit wins.
Threshfield motorists: how to avoid petrol in a diesel next time
- The label is what matters, and so read the petrol pump instead of the colour: in the UK unleaded handles are normally green and diesel black, but not on each forecourt.
- Many vehicles state the fuel inside the filler flap or on the cap, so check there on your first fill in a motor you do not know.
- Label the key. In a house with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of intending to remember.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump. It seems daft and it does the trick.
- Whilst you're thinking about something else, this is an easy mistake to make — so put your phone away.
- Some diesels have a filler designed to block a petrol nozzle, and devices you can add are available for cars without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop checking the pump.
- Noticing it mid-fill? Stop there and then. A thinner mixture results from less petrol inside the tank, yet your next stage remains the same: do not fire it up.
Put petrol in a diesel in Threshfield already?
In that case, there's only a short order of things. Leave it unstarted, with your ignition off as well. Ask the attendants to help you push it clear of the pump if you are still at the forecourt, whether that is Shell or anywhere else. Call 0333 366 0103 next, with three answers — the fuel, the rough amount, and whether it's run.
If it was AdBlue instead of petrol, say so. That's a separate problem — corrosion and deposits and not lost protection — and it has its own page for Threshfield.
Threshfield petrol in a diesel jobs: why one costs more than another
There's no fair single price for this, since the four scenarios above are four separate jobs. Chiefly, your cost moves with which one you are in. Two things follow that: the petrol that went in as a proportion of what the tank takes, then the spot the car is in and whether a van can reach it safely.
That's why we ask three queries before quoting rather than after: what went in, how much, and if it's run. With those replies, you get a straight figure rather than a range.
About Threshfield, for a moment
Threshfield is a village situated in North Yorkshire, on the banks of a river at an elevation of 194 metres. Threshfield lies approximately 20 miles from Ripon and 193 miles from London, with nearby villages including Linton and Skirethorns. Threshfield has a population of around 631 people, predominantly living in terraced housing. Threshfield is surrounded by scenic countryside, with Thorpe Fell View nearby.
Threshfield and North Yorkshire: where our fuel drain cover runs
Linton, Skirethorns and Thorpe Fell View are among the spots around Threshfield that the same teams work, answering petrol in diesel calls across Threshfield's BD postcode area. We drain where your car is — your own drive, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
Still at the pump around Threshfield?
The best place there is, then — that is where you are. Ring, and keep it switched off.