How Worried Should You Be? Petrol in a Diesel Car in New Mill
Provided it hasn't been started, you can worry far less than you likely are. Till your ignition primes your pump, the starter cranks, or the car is driven, petrol in a diesel tank simply waits there and does no harm. Which means the honest reply to that first New Mill query — "have I ruined it?" — normally no. To leave the vehicle like that, ring Petrol in Diesel then leave your engine switched off. The rest of this page explains what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
The motor and petrol in a diesel: what happens
On its way through a motor, diesel does two jobs. Before it ignites, it protects — then it burns. Built to very fine clearances, the fuel injectors and the pump depend on your diesel moving through them to keep their surfaces from wearing against one another.
Petrol handles the first job poorly and the second not at all. It is thinner than diesel and takes away the protection the fuel system rests on, so a pump running on a petrol mixture is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That's where the clattering comes from.
Seen together, they make clear what shape the issue takes. It's circulation that causes the harm, not contact. All a tank with petrol in it amounts to is a fuel issue. Once your pump has been running on that petrol, a mechanical issue has begun: anything shed by a pump that is wearing is carried downstream to the fuel injectors with the fuel.
How bad is petrol in a diesel? Four scenarios our engineers see around New Mill
Fuelled but not once started — as good as it gets. Only the tank has petrol in it, and so the task is clearing the tank and cleaning the system where your car stands. This situation can only really happen at a forecourt: anywhere else, the vehicle got there by being driven.
Ignition on, or started for a second. With the system primed, the fuel lines and filter now contain petrol that has come from your tank. Still usually easy: drain, flush, and the fuel filter sorted.
A couple of miles driven, and your pump has spent every one of them labouring on diluted fuel. Distance is only half of it; how hard it was driven counts just as much. Either way the work includes your tank, your lines, the fuel filter and fresh fuel through the entire system. A school run to Dundale Primary School and Nursery is one matter. A run as far as St Albans, under 15 miles away, is a very different job. So is any mileage on the M1, under 15 miles from New Mill, where the engine has been running hard the whole time.
Driven until it protested. Knocking, a lumpy idle, smoke, a throttle that has gone soft. That's your motor telling you its fuel has stopped behaving like diesel. Whether it's the verge on Chapel Meadow, a lay-by or a side road, stop there then leave it. Long-term damage is very rare if a vehicle is stopped early, and the drain and flush that still come first take care of it.
Petrol in a diesel stories New Mill motorists hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. Nothing is removed by topping up — you are left with a bigger tank, still the same mixture. The assumption behind that guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
If anything, the reverse is true. Myth: "A newer diesel can cope with a bit of petrol." At higher pressure, through more precise components: that is how a current diesel moves its fuel, so the protection matters more, not less.
Myth: "If it starts and drives, there is no damage done." This is the one that fools drivers. Feed diesel to a petrol motor and it generally will not run, and so the driver stops — and the damage stops with them. While your pump wears, a diesel fed petrol usually starts, idles and drives away as if nothing has happened. Fine and running aren't the same thing.
An old workaround for a separate fault is behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." It doesn't put back what petrol has diluted, and the petrol is still inside your tank afterwards.
Myth: "Drain the tank yourself and you are sorted." Once the motor has been run, some of that petrol is no longer inside that tank: it's in the filter and your lines, and it goes right back through the pump at your next start. It is also genuinely risky to drain petrol into a can at the kerbside.
How it happens: petrol in a diesel
Nobody does it on purpose, and it is rarely carelessness. One way only, since of the nozzles: the smaller petrol one slips inside a diesel filler with almost no resistance, whereas the diesel one generally will not fit a petrol car. That's how the forecourt makes it simple.
It takes place when routine and the vehicle stop matching. Hire cars, courtesy cars, and vehicles that are new to you. A household with one petrol and one diesel on the drive. The pumps in a different order on a familiar forecourt. Rushing for a train outside Tring and filling up en route. Exactly the moment it takes place: after years of driving petrol, a driver fills a diesel Volkswagen Tiguan for the first time. With rain, a call arriving, or a car full of children to deal with, your hand just does what it has always done.
Next time you fill up around New Mill: preventing petrol in a diesel
- A green handle for unleaded and black for diesel is normal in the UK — yet not on each forecourt. Go by the label on the pump, not the colour.
- In a car you do not know, look inside the flap over the filler or at the cap before your first fill: plenty of motors state the fuel there.
- A coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember, in a household with one of each.
- It sounds daft and it works: on the first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the petrol pump.
- Mistakes like this are easy to make whilst your mind is on something else, so the phone goes away.
- Some diesels have a filler built to reject a petrol nozzle, and devices you can add are available for cars without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop reading the petrol pump.
- Less petrol means a thinner mix, so stop as soon as you notice — while remembering that your next stage is unchanged. It is still not to fire it up.
Put petrol in a diesel around New Mill already?
Short and simple, then, is the order of things. Don't start it, and do not turn your ignition on. If you are still on the forecourt — Shell or anywhere else — ask the staff to help you roll the car away from the petrol pump. Call 0333 366 0103 next, with three answers — your fuel, the approximate quantity, and whether it's run.
Say so if it was AdBlue instead of petrol: it is a separate fault, with its own page for New Mill, because AdBlue brings corrosion and deposits instead of lost lubrication.
What makes one New Mill petrol in a diesel job cost more than the next
Four different jobs sit behind the four scenarios above — which is why there is no honest single price. What moves the cost is chiefly which of them you're in. The proportion counts next, meaning how much of the tank is petrol, followed by the position of the vehicle and whether reaching it is safe for a technician.
That is why our technicians ask three queries before pricing rather than after: what went in, how much, and if it has run. Their replies are what turn a range into one firm number.
About New Mill
New Mill is a suburban area situated on the lakeside in Hertfordshire, with an elevation of around 120 metres. New Mill lies approximately 30.8 miles from London and 14.2 miles from St Albans, near other local places such as Tring Wharf, Little Tring, and Tringford. New Mill has a population of around 2914 people and is characterised by predominantly terraced housing.
New Mill and Hertfordshire: where our fuel drain cover runs
Tring Wharf, Little Tring and Tringford are among the places near New Mill that the same teams work, answering petrol in diesel call-outs across New Mill's HP postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations we work, and the car does not need to come to us.
Still at the pump in New Mill?
Then you are in the best place there is. Keep it off. Call.