Should You Worry? Petrol in a Diesel Car in Pen-y-lan
Not started? Then less anxious than you probably are. Till your ignition primes the pump, your starter cranks, or your car is driven, petrol in a diesel tank simply waits there and does no harm. Which makes the honest reply to the first Pen-y-lan query — "have I wrecked it?" — usually no. Keep it that way: leave your motor off and ring Petrol in Diesel. What petrol actually does to a diesel, how to judge how far it has travelled, and how to stop it from happening again: that is the rest of this page.
Petrol in a diesel: what does it do to your engine?
Passing through a motor, diesel does two things at the same time. Lubricating comes before burning; it does both. What keeps the surfaces inside your high-pressure pump and the injectors from wearing down against one another is your diesel flowing through them — they are built to extremely fine clearances.
Of those two jobs, petrol handles the first poorly and the second not at all. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump running on the blend wearing itself. It's also made to resist igniting under compression — the reverse of what a diesel needs — which is where you hear the clattering.
Put those together and the shape of the problem is plain. Contact does not do the damage — movement does. All a tank with petrol in it amounts to is a fuel fault. A pump that has been working on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with the fuel to the injectors downstream.
Pen-y-lan, petrol in a diesel: four situations, from mild to significant
Fuelled up, not once started. The best case there is. The petrol is inside your tank and just your tank, and the task is a drain and a flush where your car stands. This is the one situation that can only truly take place at a forecourt, because anywhere else the vehicle has been driven to get there.
Ignition on, or started for a moment. Petrol has come out of the tank and got to your filter and your lines, because the system has been primed. Still normally straightforward: drain, flush, and your filter dealt with.
A few miles driven, and the pump has spent each of them labouring on diluted fuel. Mileage is only half of it; how hard it was driven counts just as much. Either way this work runs to your tank, your lines, your filter and fresh fuel through the whole system. Driving the kids to the local primary school is one sort of trip. Very different again: a trip to Cardiff, under 3 miles away, or any distance on the A48(M), under 3 miles from Pen-y-lan, where the engine kept labouring hard.
Driven until it complained. Clattering, an uneven idle, smoke, a throttle that has gone soft. The engine is telling you your fuel is no longer behaving like diesel. Leave it wherever it stops: a lay-by, a quiet street, the verge on Greenlawns. What comes first is still the drain and flush, and that deals with it, with lasting damage very rare if a car is stopped quickly.
Myths Pen-y-lan motorists hear about petrol in a diesel
"Top it up the rest of the way with diesel and it will be fine" — a myth. It won't. A bigger tank of the same mixture is all it gives, because topping up takes out nothing. The assumption behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
If anything, the opposite holds. Myth: "A newer diesel can cope with a bit of petrol." A newer diesel runs its fuel through smaller components at higher pressure, which makes the lubrication matter more, not less.
"It starts, it drives, so there is no harm" — the myth that catches most motorists than any other. A petrol engine fed diesel usually will not run, so the motorist stops and the damage stops with them. While the pump wears, a diesel fed petrol normally starts, idles and drives away as though nothing has happened. Being able to run is not proof of being fine.
An old fix for a different fault lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." What petrol has diluted stays weakened, and the petrol stays inside the tank regardless.
If the engine has run, part of that petrol is in the fuel filter and the lines, not the tank — and your next start pulls it straight back through the pump. So the myth "drain your tank yourself and you are sorted" doesn't stand up. Also, a can of petrol filled at the kerbside is genuinely hazardous.
Petrol in a diesel: how does it occur?
It's seldom carelessness, and nobody does it on purpose. A diesel nozzle mostly will not go into a petrol motor, but the narrower petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one error simple, and only in that direction.
Routine and the vehicle getting out of step is how it takes place. A new motor, a hire car or a courtesy car. A household with one petrol and one diesel on the driveway. The pumps in a different order on a well-known forecourt. Filling up in a rush on the way to Cathays, with a train to catch. The first fill-up in a diesel Renault Megane after years of driving petrol is exactly the moment it happens. Add rain, a phone call or a back seat full of kids, and the hand repeats what it has always done.
How to avoid petrol in a diesel at your next fill-up in Pen-y-lan
- Not every forecourt in the UK follows green for unleaded and black for diesel, even if most generally do. Check the pump's label; the colour is only a hint.
- Check your filler flap. Plenty of vehicles state the fuel type inside the flap or on the cap. Look at it on the first fill in any motor you don't know.
- One of each in the household? Mark the key to your diesel — a coloured fob, a sticker — because intending to remember isn't enough.
- "Diesel", out loud, before you lift the nozzle — each time a new or hired car gets its first tank. It sounds silly. It works.
- Thinking about something else is when this becomes an easy mistake to make, so put your phone away then keep your mind on the petrol pump.
- Some diesels come with a filler built to reject a petrol nozzle, and devices you can add are available for vehicles without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the petrol pump.
- Less petrol makes a thinner mix, so stop as soon as you realise — while remembering that your next stage is unchanged. It is still not to start the vehicle.
Pen-y-lan: already put petrol in a diesel?
Then, there's just a short order of things. Leave it unstarted, with your ignition switched off as well. Yet on the forecourt, at Sainsbury's or anywhere else? Ask the staff to help you roll the vehicle clear of the petrol pump. Next, 0333 366 0103. We will ask what went in, about how much, and if it has been run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a separate problem — Pen-y-lan has a page just for it.
One petrol in a diesel job in Pen-y-lan costs more than another. Why?
There is no fair single price for this, since the four situations above are four separate jobs. Mostly, your cost moves with which one you're in. Two things follow that: the petrol that went in as a share of what that tank takes, then the spot the car is in and whether a technician can reach it safely.
Three questions come first, before any quote, instead of after — what went in, how much, has it run — and that is the reason. A range becomes a straight figure when the answers are in.
About Pen-y-lan, for a moment
Pen-y-lan is a suburban area in Cardiff, situated near the coast and approximately 1.8 miles from the city centre. Pen-y-lan sits at an elevation of 56 metres, overlooking the surrounding area, and is close to nearby places such as Roath, Llanedeyrn, and Roath Park. Pen-y-lan is characterised by its predominantly semi-detached housing stock, which reflects the area's residential nature. Pen-y-lan is also relatively close to the Welsh capital's amenities, while being far enough from London, at 130.4 miles away, to maintain a distinct local identity.
Fuel drain cover in Pen-y-lan and across Cardiff
Petrol in diesel call-outs around Pen-y-lan — part of the CF postcode area — go to teams that also cover the locations round it, Roath, Llanedeyrn and Roath Park among them. Our technicians drain where the vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
In Pen-y-lan and still at the pump?
The best spot there is, then — that is where you are. Keep the vehicle turned off, and ring.