How Worried Should You Be? Petrol in a Diesel Car in Two Locks
Far less than you probably are, provided it has not been started. Till your ignition primes the pump, your starter turns, or your car is driven, petrol in a diesel tank just sits there and does no harm. Which means the truthful reply to the first Two Locks question — "have I wrecked it?" — normally no. Petrol in Diesel is who to ring, with the engine kept off, and so it stays that way. Keep reading for three things: the effect petrol has inside a diesel engine, the signs of how far it has spread, and ways to make sure you never do it again.
Inside your engine: what petrol in a diesel really does
Passing through an engine, diesel does two things at the same time. It combusts, and before it combusts it lubricates. The high-pressure pump and the fuel injectors are designed to very fine gaps, and your diesel passing through them is what keeps those surfaces from wearing down against each other.
Of these two jobs, petrol handles the first badly and the second not at all. It is thinner than diesel and removes the protection the system rests on, and so a pump running on a petrol mixture is a pump wearing itself. And petrol is made to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That's where the knocking comes from.
Seen together, they make clear what shape the issue takes. Not contact but movement is what causes the harm. Where the petrol is only inside that tank, it's a problem of fuel, nothing more. Whatever a worn pump sheds travels on, carried by the fuel, into the fuel injectors further along, which is why a pump that has been working on the petrol is where a mechanical issue starts.
Petrol in a diesel in Two Locks: how bad is it? Four cases
Fuelled, and not started: no case is better. That petrol is in that tank and only your tank, and the job is a drain and a flush where the vehicle stands. This is the one situation that can only really take place at a forecourt, as anywhere else the car has been driven to get there.
Ignition on, or started for a moment. With the fuel system primed, the fuel lines and filter now contain petrol that has come from that tank. Usually little more than draining, cleaning and sorting the fuel filter, and so still easy.
Those few miles on the road meant your pump working on fuel diluted by petrol throughout. Tank, lines, filter, then clean fuel run through the entire circuit: that's the work, and the way the car was driven matters as much as the mileage. Short trips, like the school run to the local primary school, are one thing. Getting as far as Newport, under 5 miles away, makes a very different task — as does any miles on the M4, under 3 miles from Two Locks, with the motor running hard the whole time.
Driven on until it complained — knocking, smoke, an uneven idle, a soft throttle. What you are hearing is the motor signalling fuel that no longer runs like diesel. Pull up where you are — on the verge on Llwyn Celyn, at the kerb, down a side road — and don't move it again. A car stopped soon very rarely has long-term damage, because the drain and the flush-through, which still come first, deal with it.
Stories Two Locks people hear about petrol in a diesel
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Nothing is removed by topping up — you're left with a fuller tank, still the same mix. Percentage isn't how a diesel fuel system copes with petrol, however much that advice assumes.
"Modern diesels can handle a little petrol" — a myth, and closer to the opposite. A newer diesel runs its fuel through smaller parts at higher pressure, which makes the lubrication count more, not less.
This is the one that fools motorists. Myth: "If it starts and drives, there's no damage done." Diesel in a petrol motor usually means a motor that will not run: the driver stops, and so does the harm. While your pump wears, a diesel fed petrol normally starts, idles and drives away as though nothing has happened. Fine and running aren't the same at all.
Not so: a two-stroke additive makes it safe to drive home. It is an old fix, meant for another fault. None of what petrol weakened is put back by it — and later, the tank still holds that petrol.
If the engine has been run, part of the petrol is in your filter and the fuel lines, not that tank — and your next start sends it right back through your pump. So the myth "drain your tank yourself and you are sorted" doesn't hold. Draining petrol into a can by the kerbside is also truly dangerous.
Petrol in a diesel: how does it occur?
No one does it on purpose, and it is rarely carelessness. A diesel nozzle mostly won't go into a petrol vehicle, yet the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one error easy, and just in one direction.
The moment routine stops matching the vehicle is the moment it takes place. Hire cars, courtesy cars, and motors that are new to you. One petrol and one diesel on the drive of the same household. The pumps in a different order on a well-known forecourt. A rushed fill on the way to Cwmbran with a train to catch. Years of petrol cars behind you, a diesel Renault Megane in front of you on the forecourt for its first tank — that's when. Throw in a back seat full of kids, a phone call or rain, and habit takes over.
Two Locks drivers: how to avoid petrol in a diesel next time
- The label is what matters, and so read the pump rather than the colour: in the UK unleaded handles are normally green and diesel black, yet not on every forecourt.
- In a car you do not know, look inside the flap over your filler or at the cap before your first fill: plenty of cars state the fuel type there.
- One of each in the house? Label the key to the diesel — a coloured fob, a sticker — since meaning to remember is not enough.
- It sounds silly and it works: on the first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the pump.
- Mistakes like this are simple to make while your mind is on something else, so your phone goes away.
- Add-on devices are available for cars without one, and some diesels come with a filler that will not take a petrol nozzle. Useful — but a backstop only, never a reason to stop checking the label.
- As soon as you notice, stop: less petrol inside your tank makes a weaker blend. What to do next does not change, though — still don't crank it.
Petrol already in a diesel around Two Locks? Start here
The order of things is brief, then. Don't turn your ignition on, and do not crank it. The attendants on the forecourt — whether at Shell itself or wherever you filled up — will normally help push it clear of the pump if you ask. Then phone 0333 366 0103 and tell us what was put in, about how much, and if it has run.
Corrosion and deposits are the problem with AdBlue, where petrol brings lost lubrication. So if it was AdBlue, say so — and read its own Two Locks page.
What makes one Two Locks petrol in a diesel job cost more than the next
Four separate tasks sit behind the four scenarios above — which is why there's no honest single price. What moves your cost is mostly which of them you're in. Where the car is counts too, and whether a technician can safely get to it, after the ratio of petrol to what the tank takes.
What was put in, how much, and if it has run — three questions our engineers ask before costing, not after, for precisely that reason. With the answers, there is a straight figure instead of a range.
About Two Locks, for a moment
Two Locks is a suburban area in Torfaen, situated on the riverside at an elevation of 64 metres, with terraced housing being the predominant type of accommodation. Two Locks is located near the city of Newport, approximately 4 miles away, and is close to nearby places such as Ty Coch, St Dials, and Hollybush. Two Locks has a population of around 5665 people and is part of the wider urban area surrounding Newport.
Fuel drain cover around Two Locks and across Torfaen
Two Locks sits in the NP postcode area, and the teams that answer petrol in diesel call-outs there work the places near it as well — Ty Coch, St Dials and Hollybush among them. A forecourt, a supermarket car park, a lay-by or your own drive are all places our engineers drain, and your vehicle doesn't need to move to us.
In Two Locks and still at the petrol pump?
In that case, you couldn't be in a better position. Call, and leave it turned off.