How Worried Should You Be? Petrol in a Diesel Car in The Crescent
Less than you likely are, if it hasn't been started. Everyone in The Crescent starts with "have I ruined it?", and the fair answer is generally no: petrol left in the tank of a diesel remains harmless until priming, cranking or driving pulls it into the fuel system. To keep the car that way, phone Petrol in Diesel and leave the motor switched off. The rest of this page explains what petrol really does to a diesel, how to tell how far it has got, and how to make sure it does not happen to you again.
The engine and petrol in a diesel: what goes on
Diesel does two tasks on its way through an engine. It ignites, and before it ignites it lubricates. The high-pressure pump and your injectors are made to very fine clearances, and the diesel passing through them is what keeps those surfaces from wearing down against each other.
Of those two jobs, petrol handles the first badly and the second not at all. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, so a pump running on the mixture wearing itself. It is also made to resist igniting under compression — the opposite of what a diesel needs — which is where you get the knocking.
Together, those make the shape of the problem clear. The harm is done by circulation, not by contact. A tank with petrol in it is a fuel problem. A pump that has been working on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the fuel injectors further on.
How serious is petrol in a diesel? Four situations our technicians see around The Crescent
Filled up, not once started. The best case there is. Just that tank has petrol in it, so the task is clearing your tank and purging the fuel system where the vehicle sits. This situation can only truly take place at a forecourt: anywhere else, your car got there by being driven.
Started for a moment, or just the ignition on. With the system primed, your lines and filter already contain petrol that has come from your tank. Still usually straightforward: drain, flush, and the filter seen to.
The pump now spent a couple of miles on thinned fuel — that is what driving it does. The work is the tank, the lines, your filter and fresh fuel through the whole system, and how hard your car was driven counts as much as how far. The school run to St Mary's Church of England Primary School, Hinckley is one thing. A run as far as Coventry, under 15 miles away, is a very different job. So is any distance on the M69, under 3 miles from The Crescent, where the motor has been working hard throughout.
Driven on till it protested — knocking, smoke, a ragged idle, a dead throttle. That's the motor telling you its fuel has stopped acting like diesel. Stop wherever you are — the verge on Brunel Road, a lay-by, a side street — and leave the vehicle there. The drain and flush still come first, and they take care of it: if a car is stopped quickly, permanent damage is very uncommon.
Myths The Crescent drivers hear about petrol in a diesel
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. Topping up takes out nothing; it gives you a fuller tank of the same mixture. That guidance assumes a diesel fuel system handles petrol by percentage. It doesn't.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the opposite. Smaller parts and higher pressure are the way a modern diesel runs its fuel, and that makes the lubrication count more, not less.
Myth: "If it starts and drives, there is no damage done." This is the one that fools motorists. Feed diesel to a petrol motor and it generally will not run, so the driver stops — and the damage stops with them. Whilst your pump grinds, a diesel fed petrol usually starts, ticks over and drives away as though nothing has happened. Fine and running are not the same thing.
An old fix for a different issue lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol thinned is put back by it — and later, your tank still holds the petrol.
Myth: "Drain the tank yourself and you are sorted." Once the engine has been run, some of the petrol is no longer in your tank: it's in the filter and your lines, and it goes right back through your pump on the next start. Also, a can of petrol filled at the kerbside is truly hazardous.
Petrol in a diesel: how does it happen?
On purpose? Never. Through carelessness? Rarely, if ever. A diesel nozzle generally will not fit a petrol car, yet the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one error easy, and just in that direction.
The moment habit stops matching your car is the moment it happens. Courtesy car, hire car, or a vehicle that is new. Two motors on one drive, one petrol, one diesel. A well-known forecourt with the pumps in a different order. A hurried fill en route to Hinckley with a train to catch. Years of petrol vehicles behind you, a diesel Renault Megane in front of you at the forecourt for its first tank — that's when. With rain, a call coming in, or a car full of children to deal with, the hand just does what it always has.
How to prevent petrol in a diesel at your next fill-up around The Crescent
- Check the pump, not the colour. In the UK unleaded handles are normally green and diesel black, but not on every forecourt. The label is what counts.
- The first fill in a strange motor is the time to check your filler flap — on it, or on the cap, plenty of vehicles state which fuel to use.
- Mark your key. In a household with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember.
- "Diesel", aloud, before you pick up the nozzle — every time a new or hired car needs its first tank. It seems daft. It does the trick.
- Mistakes like this are easy to make while your mind is on something else, and so your phone goes away.
- Some diesels have a filler designed to refuse a petrol nozzle, and devices you can add are available for motors without one. Such an inhibitor helps up to a point — as a backstop, not a reason to stop checking the pump.
- Less petrol makes a weaker mixture, and so stop the moment you realise — while remembering that your next stage is unchanged. It's still not to fire it up.
Petrol already in a diesel around The Crescent? Begin here
Then the order of things is brief. Do not start it, and do not switch the ignition on. Still at the forecourt, at Tesco or anywhere else? Ask the staff to help you push the car away from the petrol pump. Call 0333 366 0103 next, with three answers — your fuel, the rough quantity, and if it has run.
If it was AdBlue rather than petrol, say so. That is a different fault — corrosion and deposits instead of lost protection — and it has its own page for The Crescent.
Why one petrol in a diesel task around The Crescent costs more than another
There is no fair single quote for this, because the four scenarios above are four different tasks. Mostly, the cost moves with which one you are in. The proportion counts next, meaning how much of that tank is petrol, followed by the location of the car and whether getting to it is safe for our van.
That is why our technicians ask three queries before quoting rather than after: what went in, how much, and whether it has run. Those replies are what turn a range into one firm number.
About The Crescent
The Crescent is a locality situated on the riverside in Leicestershire, with an elevation of around 115 metres. The Crescent lies near several nearby places, including Hinckley, Sketchley, and Hollycroft, and is approximately 10.7 miles from Coventry. The Crescent is characterised by a high proportion of flat housing, and its population is around 4351 residents. The Crescent is also relatively close to London, at a distance of 88.8 miles.
Across Leicestershire and in The Crescent: fuel drain cover
Hinckley, Sketchley and Hollycroft are among the places near The Crescent that the same teams work, answering petrol in diesel jobs across The Crescent's LE postcode area. A forecourt, a supermarket car park, a lay-by or your own drive are all places our technicians drain, and your car does not need to come to us.
In The Crescent and still at the petrol pump?
Then, you couldn't be in a better place. Keep it off. Call.