Petrol in a Diesel Car in Newport: How Worried Should You Be?
Probably less than you already are — provided no one has started it. Until the ignition primes your pump, your starter cranks, or your car is driven, petrol in a diesel tank just sits there and does nothing. Which makes the truthful reply to that first Newport query — "have I ruined it?" — normally no. Leave your engine off then phone Petrol in Diesel — that is how you keep it like that. What petrol actually does to a diesel, how to judge how far it's travelled, and how to keep it from happening a second time: that's the rest of this page.
Inside the motor: what petrol in a diesel really does
Passing through an engine, diesel does two things at once. Lubricating comes before burning; it does both. What stops the surfaces inside the high-pressure fuel pump and the fuel injectors from wearing against each other is your diesel passing through them — they're designed to very fine tolerances.
Badly at the first, not at all at the second: that is petrol. It is runnier than diesel and takes away the lubrication the fuel system depends on, so a pump running on a petrol blend is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That is where the knocking comes from.
Put those together and the shape of the trouble is plain. The harm is done by circulation, not by contact. All a tank with petrol in it amounts to is a fuel issue. The start 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 your injectors beyond it.
Four scenarios our technicians see in Newport: how bad is petrol in a diesel?
Fuelled, and not started: no case is better. At a forecourt, and really only there, that petrol is still limited to that tank — because everywhere else the vehicle was driven to reach it. The job is draining and rinsing on the spot.
A moment's running, or just the ignition on. Once primed, the system has drawn petrol from the tank up to your filter and the fuel lines. That is usually still an easy job — a drain, a flush, and the fuel filter dealt with.
The pump has worked a few miles on weakened fuel — that's what driving the vehicle does. Tank, lines, filter, then fresh fuel put through the entire circuit: that is the work, and the way your car was driven counts as much as the distance. Short trips, such as the school run to the local primary school, are one thing. Getting as far as St Davids, under 25 miles away, makes a very different job — as does any miles on the M4, under 50 miles from Newport, with the engine running hard the whole time.
Driven on till it protested — knocking, smoke, an uneven idle, a dead throttle. That is your engine telling you its fuel no longer is behaving like diesel. Leave it where it stops: a lay-by, a side street, the verge on Market Street. The drain and flush-through still go first, and they take care of it: if a vehicle is pulled over soon, lasting damage is very uncommon.
Newport drivers and that petrol in a diesel myths they 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're left with a bigger tank, still the same mix. The assumption behind that advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the opposite. More precise parts and higher pressure are how a newer diesel runs its fuel, and that makes the lubrication count more, not less.
Myth: "If it starts and drives, there is no harm done." This is the one that catches drivers. Any petrol motor fed diesel usually will not run, and so the driver stops and the damage stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile your pump grinds. Being able to run is not proof of being fine.
An old workaround for a distinct fault lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." The petrol is still in the tank after that, and what it has diluted is not put back.
"Drain it yourself and you're sorted" — a myth, since after it's been running some petrol sits in your filter and lines, waiting to go right back through your pump on your next start. Besides, petrol cleared into a can by the road is truly hazardous.
How petrol ends up: petrol in a diesel
Carelessness is seldom the cause, and nobody means to do it. The petrol nozzle is the narrower of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol car at all. The forecourt makes it simple, and the slip runs one way.
Routine and the car falling out of step is when it takes place. Courtesy car, hire car, or a vehicle that's brand new. One petrol and one diesel on the driveway of the same household. A familiar forecourt with the pumps in a different order. A train to catch, and a rushed fill on the way to Fishguard Harbour. A new-to-you diesel Renault Megane, its first fuelling, and a motorist used to petrol: precisely when it happens. Add rain, a phone call or a back seat full of children, and the hand repeats what it has always done.
Newport people: how to avoid petrol in a diesel next time
- The label is what matters, so read the pump instead of the colour: in the UK unleaded handles are normally green and diesel black, but not on every forecourt.
- Check the filler flap. Many vehicles state the fuel inside the flap or on the cap. Look at it on the first fill in any motor you don't know.
- Mark your key. In a home with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember.
- It seems 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.
- Tuck your phone away. This is an easy mistake to make while you are thinking about something else.
- 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 motors without one. They are a backstop, not a reason to stop checking the petrol pump.
- Less petrol makes a thinner mix, so stop as soon as you realise — though remembering that your next step is unchanged. It is still not to crank it.
Newport: already put petrol in a diesel?
Short and simple, then, is the order of things. Leave it unstarted, with the ignition switched off as well. Ask the attendants to help you roll it clear of the petrol pump if you are still on the forecourt, whether that is Murco or anywhere else. Then ring 0333 366 0103 and tell us what got in, about how much, and if it has run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a different fault — Newport has a page just for it.
What makes one Newport petrol in a diesel job cost more than the next
There's no fair single quote for this, since the four situations above are four different jobs. The situation itself does most of the work of moving your cost. Next it's the proportion — how much petrol got in against how much your tank takes — and then where the vehicle is and whether our van can get to it safely.
That is why our engineers ask three queries before quoting instead of after: what got in, how much, and whether it's run. With the replies, there is a straight figure rather than a range.
About Newport
Newport is a small coastal town in Pembrokeshire, situated on the north coast of Wales at an elevation of around 35 metres. Newport sits near the mouth of the River Nevern, close to the villages of Parrog and the historic site of Cippin Stone. Newport is characterised by its predominantly detached housing stock, reflecting its role as a residential centre for the local community. Newport is located approximately 20 miles from St Davids, the smallest city in the UK.
Fuel drain cover across Pembrokeshire, Newport included
Our vans answering petrol in diesel call-outs around Newport, in the SA postcode area, equally work the places around it, Parrog, Cippin Stone and Nevern 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.
Newport: still at the petrol pump?
The best spot there is, then — that is where you are. Keep it off. Ring.