Glynfach: Petrol in a Diesel Car? How Worried to Be
Less than you likely are, if it hasn't been started. Everyone in Glynfach starts with "have I ruined it?", and the honest answer is generally no: petrol left inside your tank of a diesel stays harmless till priming, cranking or driving draws it into the system. Keep it like that: leave your motor off and phone Petrol in Diesel. Further down, this page sets out what petrol really does inside a diesel, how far it might have got, and how to stop it happening to you a second time.
Inside the motor: what petrol in a diesel does
Passing through a motor, diesel does two things at once. It burns, and before it burns it lubricates. Extremely fine clearances are built into the injectors and your high-pressure pump, and just the diesel flowing through keeps those surfaces from grinding together.
Of those two tasks, petrol handles the first badly and the second never. A pump working on a petrol mixture is wearing itself out, since petrol is thinner than diesel and takes away the protection your fuel system depends on. Petrol is also made to resist igniting under compression — the reverse of what a diesel needs from its fuel — and that's where the clattering starts.
Put these together and the shape of the issue is clear. The harm is done by circulation, not by contact. Petrol in a tank is a fuel fault. Whatever a worn pump sheds goes on, carried by your fuel, into your injectors downstream, which is why a pump that has worked on that petrol is where a mechanical issue starts.
Four scenarios we see in Glynfach: how serious is petrol in a diesel?
Filled up, and never started: nothing beats it. Being on a forecourt is what makes this the case: elsewhere, the car has been driven there to begin with. With that petrol held inside your tank alone, it is drained and flushed right where it stands, and nothing more is needed.
A moment's running, or merely your ignition on. With the fuel system primed, the fuel lines and filter now contain petrol that has come from your tank. Normally nothing more than draining, rinsing and sorting your filter, and so still straightforward.
Driven a few miles. Now the pump has spent those miles running on thinned fuel. How hard your car was driven counts as much as how far, and the work takes in that tank, the fuel lines, your filter and fresh fuel through the whole system. On the school run to the local primary school, the mileage is short. Any mileage on the M4, under 10 miles from Glynfach, means the engine working hard throughout, and a run to Cardiff, under 15 miles away, makes a very different job as well.
Driven on till it complained — rattling, smoke, an uneven idle, a soft throttle. That's your engine telling you its fuel no longer is behaving like diesel. Stop on the spot — on the verge on Glynfach Road, at the kerb, down a side road — and do not move it. What comes first is still the drain and flush-through, and that sorts it out, with long-term damage very uncommon when a car is stopped quickly.
Petrol in a diesel stories Glynfach drivers hear
Myth: topping up to full with diesel makes it fine. It does not. Nothing is removed when you top up — the tank just holds more of the same mixture. The idea behind the guidance — that diesel fuel systems accept petrol by percentage — is wrong.
"Modern diesels can handle a little petrol" — a myth, and nearer the reverse. Lubrication counts more on newer diesels, not less, since their fuel runs through more precise parts at higher pressure.
Myth: "If it starts and drives, there is no harm done." This is the one that fools people. A petrol engine fed diesel normally won't run, and so the motorist stops and the harm stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually will; meanwhile your pump wears. A running engine does not mean fine.
An old fix for a different fault lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol thinned gets put back by it — and later, the tank still contains that petrol.
If your engine has run, part of the petrol sits in your filter and the fuel lines, not that tank — and your next start pulls it straight back through your pump. So the myth "drain that tank yourself and you are sorted" doesn't stand up. On top of that, petrol emptied into a can by the road is truly risky.
Petrol in a diesel: how does it take place?
It's seldom carelessness, and nobody does it on purpose. The petrol nozzle is the narrower of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol vehicle at all. The forecourt makes it easy, and the error runs one way.
When habit and the car stop matching, it takes place. A new car, a hire car or a courtesy car. Two motors on one drive, one petrol, one diesel. A forecourt you know, only with its pumps arranged differently. Racing for a train at Porth and filling up en route. The first fill-up in a diesel Renault Megane after years of driving petrol is exactly the moment it happens. With rain, a call coming in, or children to deal with, your hand just does what it always has.
Glynfach motorists: how to prevent 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 each forecourt.
- Plenty of cars state the fuel inside the filler flap or on the cap, and so check it on your first fill in any motor you do not know.
- Label your key. In a house with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of intending to remember.
- It seems silly and it does the trick: on your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump.
- Tuck your phone away. This is an easy mistake to make whilst you are thinking about something else.
- Some diesels come with a filler built to refuse a petrol nozzle, and devices you can add exist for cars without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop checking the pump.
- Stop the moment you realise. Less petrol inside your tank makes a thinner mix. It doesn't change what to do next, which is still not to crank it.
Put petrol in a diesel in Glynfach already?
Then, there's only a short order of things. Starting it is out, and so is switching on the ignition. If you're still on the forecourt — Texaco or anywhere else — ask the attendants to help you push it away from the petrol pump. What went in, roughly how much, and whether it's run: tell us those when you ring 0333 366 0103.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost protection, make it a separate issue — Glynfach has a page just for it.
One petrol in a diesel task in Glynfach costs more than another. Why?
A fair single price does not exist here: four scenarios, four separate tasks. Chiefly, the cost shifts with which one you are in. Where your car is counts too, and whether a van can safely get to it, after the proportion of petrol to what the tank holds.
That's why we ask three queries before costing rather than after: what went in, how much, and if it's run. A range turns into a straight figure when the answers are in.
About Glynfach and where it is
Glynfach is a suburban area situated on the riverside in Rhondda Cynon Taf, with a mix of terraced housing and local amenities. Glynfach sits at an elevation of 112 metres, near the communities of Porth and Cymmer. Glynfach is located close to the city of Cardiff, which is approximately 13 miles away, and is part of the wider South Wales urban area. Glynfach has a population of around 4374 residents.
Glynfach and Rhondda Cynon Taf: where our fuel drain cover runs
Petrol in diesel call-outs around Glynfach — part of the CF postcode area — go to vans that also cover the locations round it, Porth, Cymmer and Britannia included. You need not move your car to us. Forecourts, supermarket car parks, lay-bys and your own drive are all places we drain.
In Glynfach and still at the pump?
Then you are in the best place there can be. Keep the vehicle switched off, then ring.