Tower Hill: Petrol in a Diesel Car? How Worried to Be
Probably less than you already are — as long as no one has started the vehicle. Till your ignition primes your pump, your starter cranks, or your car is driven, petrol in a diesel tank simply rests there and does no harm. Which means the truthful reply to the first Tower Hill query — "have I ruined it?" — normally no. Keep it like that: leave your motor off then phone Petrol in Diesel. The remainder of this page covers what petrol actually does to a diesel, how to tell how far it has got, and how to make sure it does not happen to you again.
What petrol in a diesel does to your engine
Two jobs fall to diesel on its journey round a motor. It protects first, and only then does it burn. What stops the surfaces inside your high-pressure pump and the fuel injectors from wearing down against one another is the diesel passing through them — they're made to very fine clearances.
Of these two tasks, petrol manages the first badly and the second never. A pump running on a petrol mix is wearing itself out, since petrol is thinner than diesel and strips out the lubrication your fuel system relies 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.
Seen together, they make clear the shape the problem takes. Not contact but circulation is what does the harm. Petrol in a tank is a fuel problem. After your pump has been working on that petrol, a mechanical issue has started: whatever is shed by a pump that is grinding travels onward to the injectors with the fuel.
Tower Hill, petrol in a diesel: four situations, from mild to significant
Fuelled up, not once started. The best case there is. On a forecourt, and truly only there, that petrol is still confined to the tank — since everywhere else the car was driven to reach it. The task is draining and purging on the spot.
Started for a second, or just your ignition on. Your system has been primed, and so petrol has left the tank and reached your filter and the fuel lines. Drain, flush, deal with the fuel filter: still normally straightforward.
Your pump has worked a couple of miles on diluted fuel — that is what driving the vehicle does. Tank, lines, filter, then fresh fuel run through the whole circuit: that's this work, and the way the car was driven counts as much as the mileage. Short trips, like the school run to Arunside School, Horsham, are one matter. Very different again: a run to Brighton and Hove, under 25 miles away, or any miles on the M23, under 10 miles from Tower Hill, where the engine never stopped labouring hard.
It complained, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone uneven. The fuel isn't acting like diesel any more, and the motor is telling you. Whether it's the verge on Tower Close, a lay-by or a side street, stop where you are and leave it. Long-term damage is very unusual if a vehicle is pulled over quickly, and the fuel drain and flush that still come first deal with it.
What Tower Hill drivers get told about petrol in a diesel — and the stories in it
Myth: topping up to full with diesel makes it fine. It does not. A fuller tank of the same mix is all it gives, since topping up removes nothing. A diesel fuel system does not accept petrol by percentage in the way that advice supposes.
"Modern diesels can handle a little petrol" — a myth, and closer to the opposite. At higher pressure, through smaller parts: that is how a newer diesel moves its fuel, so the lubrication counts for more, not less.
This is the one that catches drivers. Myth: "If it starts and drives, there's no damage done." Feed diesel to a petrol motor and it normally won't run, and so the motorist stops — and the damage stops with them. Whilst your pump wears, a diesel fed petrol normally starts, idles and drives away as if nothing has happened. Fine and running are not the same at all.
Myth: a two-stroke additive lets you to drive home. It was an old workaround, supposed for another issue. It doesn't put back what petrol has weakened, and that petrol is still in your tank afterwards.
The next start sends petrol back round the pump from the fuel lines and your filter, where some of it sits once the engine has been run. That's why a DIY tank drain does not sort it — a myth. Draining petrol into a can by the roadside is also really dangerous.
How does petrol in a diesel occur?
Nobody does it on purpose, and it is seldom carelessness. The forecourt makes it simple: the petrol nozzle is the smaller of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle mostly will not go into a petrol motor at all. So the slip runs one way.
Habit and the car falling out of step is when it occurs. A new car, a hire car or a courtesy car. Two cars on one driveway, one petrol, one diesel. The pumps in a different order on a familiar forecourt. Fuelling up in a hurry en route to Christs Hospital, with a train to catch. Years of petrol cars behind you, a diesel Renault Megane in front of you at the forecourt for its first tank — that is when. Add rain, a phone call or a back seat full of children, and your hand repeats what it has always done.
Tower Hill motorists: how to avoid petrol in a diesel next time
- Green for unleaded and black for diesel is normal in the UK — yet not on each forecourt. Go by the label on the petrol pump, not the colour.
- Plenty of cars state the fuel inside your filler flap or on the cap, so check it on your first fill in a car you do not know.
- A coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember, for a household with one of each.
- Before the nozzle comes off the pump the first time you fill a hired or new car, say "diesel" out loud. Daft, perhaps, but it does the trick.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck your phone away.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler designed to block a petrol nozzle, and add-on devices exist for vehicles without one. They are a backstop, not a reason to stop reading the pump.
- Spotting it halfway? Stop there and then. A weaker mix follows from less petrol in that tank, yet the next stage remains the same: don't fire it up.
Petrol already in a diesel in Tower Hill? Start here
In that case, there is just a short order of things. Starting it is out, and so is turning on the ignition. If you are still on the forecourt — Shell or anywhere else — ask the staff to help you push it away from the pump. Then ring 0333 366 0103 and tell us what got in, about how much, and if it's run.
Say so if it was AdBlue instead of petrol: it's a separate problem, with its own page for Tower Hill, because AdBlue brings corrosion and deposits rather than lost protection.
One petrol in a diesel task around Tower Hill costs more than another. Why?
The four situations above are four separate jobs, so no single price for this would be honest. The scenario itself does most of the work of moving your cost. Where the car is counts too, and whether a technician can safely get to it, after the ratio of petrol to what the tank holds.
Three questions come first, before any quote, rather than after — what was put in, how much, has it run — and that is the reason. A range turns into a straight figure when those answers are in.
About Tower Hill and where it is
Tower Hill is a small village in West Sussex, situated on the riverside at an elevation of 68 metres. Tower Hill lies near the towns of Horsham and New Town, and is connected to nearby Southwater Street. Tower Hill has a population of around 768 people, predominantly living in semi-detached housing. Tower Hill is located near Brighton and Hove, and is also within commuting distance of London, being approximately 32.7 miles away.
Across West Sussex and in Tower Hill: fuel drain cover
Petrol in diesel call-outs around Tower Hill — part of the RH postcode area — go to vans that also cover the locations around it, Horsham, New Town and Southwater Street included. Our technicians drain wherever the vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
Tower Hill: still at the pump?
In that case, you could not be in a better position. Keep it off. Phone.