Highway: Petrol in a Diesel Car? How Worried to Be
Probably less than you are now — as long as nobody has started it. Till your ignition primes your pump, your starter turns, or your car is driven, petrol in a diesel tank simply sits there and does no harm. Which makes the truthful reply to the first Highway query — "have I wrecked it?" — normally no. Leave your engine off and ring Petrol in Diesel — that is how you keep it like that. Read on for three things: the effect petrol has inside a diesel motor, the clues of how far it has spread, and the way to make sure you don't do it again.
The motor and petrol in a diesel: what goes on
On its way through an engine, diesel has two jobs. Lubricating comes before burning; it does both. What stops the surfaces inside the high-pressure pump and the injectors from wearing down against one another is the diesel flowing through them — they're built to extremely fine clearances.
Of those two jobs, petrol manages the first poorly and the second never. A pump running on a petrol blend is wearing itself out, since petrol is thinner than diesel and strips out the lubrication the fuel system relies on. Petrol is also made to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that is where the rattling comes.
Put those together and the shape of the issue is clear. The damage is done by movement, not by contact. Where that petrol is only in that tank, it is an issue of fuel, nothing more. Whatever a worn pump sheds goes on, borne by your fuel, into your injectors downstream, which is why a pump that has worked on the petrol is where a mechanical problem begins.
How bad is petrol in a diesel? Four situations our engineers see in Highway
The best case there is: filled up, never started. On a forecourt, and really only there, the petrol is still limited to that tank — since everywhere else your car was driven to get to it. The job is draining and rinsing on the spot.
A brief spell of running, or just the ignition on. Once primed, the system has pulled petrol out of your tank up to your filter and the lines. Usually little more than draining, rinsing and sorting the fuel filter, so still simple.
Driven a couple of miles. Now the pump has spent those miles working on thinned fuel. How hard the car was driven matters as much as how far, and the work covers the tank, your lines, the fuel filter and clean fuel through the entire system. On the school run to Castle Primary School, the mileage is small. A run as far as Wells, under 25 miles away, is a very different job. So is any distance on the M5, under 15 miles from Highway, where your engine has been labouring hard throughout.
Driven until it protested. Rattling, a ragged idle, smoke, a throttle that has gone soft. That's the engine telling you its fuel has stopped behaving like diesel. Whether it is the verge on Windsor Lane, a lay-by or a side street, stop where you are and leave it. What goes first is still the drain and flush, and that takes care of it, with lasting damage very uncommon if a vehicle is pulled over quickly.
Highway people and the petrol in a diesel myths they hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. Topping up takes out nothing; it gives you a bigger tank of the same mix. The idea behind the guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
"Modern diesels can handle a little petrol" — a myth, and nearer the reverse. A newer diesel runs its fuel through smaller components at higher pressure, which makes the protection matter more, not less.
This is the one that catches people. Myth: "If it starts and drives, there is no harm done." A petrol motor fed diesel generally will not run, and so the motorist stops and the harm stops with them. Feed petrol to a diesel and it usually fires up, ticks over and drives away as if nothing has happened — all the while its pump is wearing. A running engine does not mean fine.
Myth: a two-stroke additive lets you to drive home. It was an old fix, supposed for another problem. What petrol has thinned stays thinned, and the petrol stays in the tank regardless.
Once the engine has been run, part of that petrol is in the fuel filter and the fuel lines, not that tank — and your next start sends it straight back through your pump. So the myth "drain the tank yourself and you are sorted" doesn't hold. On top of that, petrol drained into a can by the road is truly dangerous.
How petrol ends up: petrol in a diesel
Nobody does it on purpose, and it is seldom carelessness. A diesel nozzle mostly won't go into a petrol car, yet the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake simple, and just in that direction.
Habit and your car falling out of step is how it happens. A new vehicle, a hire car or a courtesy car. One petrol and one diesel on the drive of the same household. The pumps in a different order on a familiar forecourt. Fuelling up in a hurry on the way to Yeovil Pen Mill, with a train to catch. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is precisely the moment it happens. Add rain, a phone call or a back seat full of children, and your hand does what it has always done.
How to avoid petrol in a diesel at your next fill-up in Highway
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most generally do. Check the pump's label; the colour is just a hint.
- Many motors state the fuel inside your filler flap or on the cap, so check there on the first fill in a vehicle you do not know.
- Mark your key. In a household with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of intending to remember.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump. It sounds daft and it does the trick.
- Tuck the phone away. This is an easy mistake to make while you're thinking about something else.
- Add-on devices exist for motors without one, and some diesels are built with a filler that will not take a petrol nozzle. Helpful — but a safety net at best, never a reason to stop checking the label.
- Spotting it halfway? Stop there and then. A weaker mix results from less petrol inside the tank, but the next stage remains the same: don't fire it up.
Petrol already in a diesel around Highway? Begin here
Short and simple, then, is the order of things. Never fire it up, and do not turn the ignition on. The attendants at the forecourt — whether at BP itself or wherever you filled up — will usually help roll it away from the petrol pump if you ask. Then phone 0333 366 0103 and tell us what went in, roughly how much, and whether it has run.
Say so if it was AdBlue rather than petrol: it's a different fault, with its own page for Highway, since AdBlue brings corrosion and deposits instead of lost lubrication.
Why one petrol in a diesel job in Highway costs more than another
There is no honest single price for this, because the four situations above are four separate jobs. Chiefly, the cost shifts with which situation you're in. The proportion counts next, meaning how much of your tank is petrol, followed by the location of your car and whether reaching it is safe for a van.
Before any quote, not after, come three queries: your fuel that went in, its volume, and if it's run. That is why. The replies change a range into a straight figure.
About Highway, briefly
Highway is a suburban area in Somerset, situated inland at an elevation of 62 metres, and is located near the towns of West Stoke, Stoke sub Hamdon, and East Stoke. Highway sits approximately 18 miles from the city of Wells and is around 119 miles west of London. Highway has a population of around 1375 people and is characterised by predominantly terraced housing.
Highway and Somerset: where our fuel drain cover runs
The vans answering petrol in diesel call-outs in Highway, in the TA postcode area, also work the places near it, West Stoke, Stoke sub Hamdon and East Stoke included. No need to move your vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all places where we work.
In Highway and still at the pump?
The best spot there is, then — that is where you are. Keep it off. Ring.