Should You Worry? Petrol in a Diesel Car in Tredomen
If it has not been started, worry far less than you probably are. Till the ignition primes the pump, your starter turns, or the vehicle is driven, petrol in a diesel tank just rests there and does nothing. Which means the truthful reply to that first Tredomen question — "have I wrecked it?" — normally no. Keep it like that: leave your motor 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 a second time: that's the remainder of this page.
Inside your engine: what petrol in a diesel really does
Passing through an engine, diesel does two things at the same time. Before it combusts, it lubricates — and then it burns. Very fine tolerances go into the injectors and your high-pressure pump, and just the diesel flowing through stops those surfaces grinding together.
Of these two jobs, petrol manages the first badly and the second never. A pump working on a petrol blend is wearing itself out, because petrol is thinner than diesel and strips out the lubrication your fuel system depends on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that's where the knocking comes.
Put these together and the shape of the issue is clear. The harm is done by movement, not by contact. Where the petrol is only inside your tank, it is an issue of fuel, nothing more. Once the pump has been running on that petrol, a mechanical problem has started: whatever is shed by a pump that's wearing travels onward to your injectors with the fuel.
Four situations our technicians see around Tredomen: how serious is petrol in a diesel?
Fuelled up, not once started. The best case there is. At a forecourt, and genuinely only there, the petrol is still confined to that tank — because everywhere else the car was driven to reach it. The task is emptying and cleaning on the spot.
A brief spell of running, or merely the ignition on. Petrol has left that tank and reached the filter and the lines, because the fuel system has been bled. That is normally still a straightforward job — a drain, a flush, and your filter dealt with.
Those few miles on the road were your pump labouring on fuel thinned by petrol the whole way. The work is that tank, your lines, the fuel filter and clean fuel through the entire system, and how hard the vehicle was driven matters as much as how far. A school run to the local primary school is one thing. Any mileage on the M4, under 10 miles from Tredomen, means the engine working hard throughout, and a run to Newport, under 15 miles away, is a very different job too.
Driven till it protested. Knocking, a ragged idle, smoke, a throttle that has gone soft. That is the engine telling you its fuel no longer is behaving like diesel. Stop wherever you are — the verge on Brynview Avenue, a lay-by, a side street — then leave the car where it is. The fuel drain and flush still come first, and they take care of it: when a car is pulled over soon, permanent damage is very uncommon.
Petrol in a diesel stories Tredomen people hear
"Top it up the rest of the way with diesel and it will be fine" — a myth. It will not. Nothing is removed by topping up — you are left with a fuller tank, still the same mix. The idea behind the guidance — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: a newer diesel copes with a bit of petrol. If anything, the reverse. Protection counts more on modern diesels, not less, because their fuel passes through finer parts at higher pressure.
Myth: "If it starts and drives, there is no damage done." This is the one that fools people. A petrol engine fed diesel normally will not run, and so the motorist stops and the damage stops with them. Feed petrol to a diesel and it usually fires up, idles and pulls away as if nothing has happened — all the while its pump is wearing. Running is not the same as fine.
Myth: a two-stroke additive makes it safe to drive home. It is an old fix, meant for another fault. What petrol has thinned stays thinned, and that petrol remains inside that tank regardless.
Once the motor has run, part of the petrol sits in the fuel filter and the lines, not your tank — and the next start pulls it straight back through the pump. So the myth "drain that tank yourself and you're sorted" does not hold. Emptying petrol into a can by the kerbside is also truly risky.
Petrol in a diesel: how does it take place?
A careless moment is seldom the cause, and nobody means to do it. One way only, because of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, while the diesel one mostly won't fit a petrol car. That is how the forecourt makes it simple.
When habit and your car stop matching, it takes place. Hire cars, courtesy cars, and cars 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 rushed fill on the way to Ystrad Mynach with a train to catch. Years of petrol motors behind you, a diesel Renault Megane 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 repeats what it has always done.
Next time you fill up around Tredomen: preventing petrol in a diesel
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most generally do. Read the pump's label; the colour is only a clue.
- Many vehicles state the fuel inside your filler flap or on the cap, and so check there on the first fill in any vehicle you do not know.
- A coloured fob or a sticker on the diesel's key achieves more than any amount of intending to remember, for a household with one of each.
- Before the nozzle leaves the petrol pump the first time you fill a hired or new car, say "diesel" out loud. Daft, yes, but it does the trick.
- While you're thinking about something else, this is an easy mistake to make — so tuck the phone away.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler designed to refuse a petrol nozzle, and add-on devices are available for vehicles without one. They are a backstop, not a reason to stop checking the petrol pump.
- The moment you realise, stop: less petrol inside the tank means a weaker mixture. What to do next does not change, though — still do not crank it.
Petrol already in a diesel around Tredomen? Start here
The order of things is brief, then. Starting it is out, and so is switching on the ignition. The attendants on the forecourt — whether at Petrol itself or wherever you filled up — will normally help push it away from the pump if you ask. What went in, about how much, and whether it's run: tell us those when you phone 0333 366 0103.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost lubrication, make it a separate issue — Tredomen has a page all for it.
Tredomen petrol in a diesel tasks: why one costs more than another
The four situations above are four different jobs, so no single quote for this would be honest. Chiefly, your cost moves with which situation you are in. Where the vehicle is matters too, and whether a technician can safely get to it, after the share of petrol to what that tank holds.
That's why we ask three questions before costing instead of after: what got in, how much, and whether it's run. The replies change a range into a straight figure.
About Tredomen
Tredomen is a suburban area in Caerphilly, situated near the banks of a river at an elevation of around 135 metres. Tredomen lies approximately 11 miles north of Newport and is close to nearby places such as Ystrad Mynach and Hengoed. Tredomen is characterized by its predominantly semi-detached housing stock and is home to a population of around 2714 people. Tredomen is also near Parc Penallta Country Park, a local area of natural beauty.
Fuel drain cover across Caerphilly, Tredomen included
Petrol in diesel jobs in Tredomen — part of the CF postcode area — go to vans that also cover the locations around it, Ystrad Mynach, Hengoed and Parc Penallta Country Park included. You need not move your vehicle to us. Forecourts, supermarket car parks, lay-bys and your own drive are all locations where we work.
Tredomen: still at the petrol pump?
Then you're in the best spot there can be. Keep the car switched off, then ring.