How Worried Should You Be? Petrol in a Diesel Car in New Town
Unstarted? Then less worried than you likely are. Until the ignition primes your pump, the starter turns, or the vehicle is driven, petrol in a diesel tank simply sits there and does no harm. Which makes the honest reply to that first New Town query — "have I ruined it?" — usually no. Petrol in Diesel is who to ring, with the engine kept off, and so it stays that way. What petrol actually does to a diesel, how to judge how far it has gone, and how to stop it from happening a second time: that's the rest of this page.
What petrol in a diesel does to your engine
Diesel has two jobs on its way through an engine. It lubricates to begin with, and after that does it burn. Designed to very fine gaps, the fuel injectors and the pump depend on the diesel moving through them to stop their surfaces wearing against one another.
Petrol handles the first job badly and the second not at all. A pump working on a petrol mixture is wearing itself out, because petrol is runnier than diesel and strips out the protection your fuel system relies on. Petrol is also made to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that's where the knocking comes.
Together, those make the shape of the problem clear. Contact does not do the damage — movement does. Where the petrol is only inside your tank, it is an issue of fuel, nothing more. Once the pump has been working on that petrol, a mechanical problem has started: anything shed by a pump that's wearing is carried downstream to your injectors with the fuel.
Petrol in a diesel around New Town: how bad is it? Four situations
The best case there can be: filled up, never started. On a forecourt, and truly only there, that petrol is still limited to the tank — since everywhere else the vehicle was driven to get to it. The job is draining and cleaning on the spot.
Started for a second, or just your ignition on. Once primed, the system has pulled petrol from that tank up to your filter and the lines. Drain, flush, deal with your filter: still usually easy.
Some miles driven, and your pump has spent each of them running on thinned fuel. The work is the tank, the fuel lines, your filter and clean fuel through the whole circuit, and how hard your car was driven counts as much as how far. The school run to Tennyson Road Primary School is one matter. Very different again: a run to St Albans, under 10 miles away, or any distance on the M1, under a mile from New Town, where the engine never stopped labouring hard.
It complained, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone uneven. What you are hearing is the engine signalling fuel that no longer behaves like diesel. Leave it where it has stopped: a lay-by, a quiet street, the verge on Old Orchard. Long-term damage is very uncommon if a vehicle is pulled over quickly, and the fuel drain and flush that still come first sort it out.
What New Town drivers get told about petrol in a diesel — and the stories in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Nothing is removed by topping up — you are left with a bigger tank, still the same mixture. That guidance presumes a diesel fuel system tolerates petrol by percentage. It doesn't.
"Current diesels can handle a little petrol" — a myth, and closer to the opposite. Finer components and higher pressure are the way a modern diesel runs its fuel, and that makes the protection matter more, not less.
The myth that catches people out: if it starts and drives, it must be unharmed. Any petrol motor fed diesel generally 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 will; meanwhile your pump grinds. Being able to run is not proof of being fine.
Myth: a two-stroke additive makes it safe to drive home. It was an old fix, meant for another problem. None of what petrol thinned gets put back by it — and afterwards, that tank still holds the petrol.
"Drain it yourself and you are sorted" — a myth, since after it's been running some petrol sits in the filter and lines, waiting to go right back through your pump at your next start. On top of that, petrol emptied into a can by the road is genuinely hazardous.
Petrol in a diesel: how does it happen?
On purpose? Never. Through carelessness? Rarely, if ever. One way only, because of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, while the diesel one mostly won't fit a petrol vehicle. That is how the forecourt makes it straightforward.
When routine and the vehicle stop matching, it takes place. Any vehicle that's new to you — a hire car, on loan as a courtesy car, or brand new. A household with one petrol and one diesel on the drive. A well-known forecourt with the pumps in a different order. A train to catch, and a hurried fill en route to Luton. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist accustomed to petrol: exactly when it occurs. Your hand repeats what it has always done once you add rain, a phone call or a back seat full of kids.
Next time you fill up around New Town: preventing petrol in a diesel
- Not every forecourt in the UK follows green for unleaded and black for diesel, even if most generally do. Check the pump's label; the colour is only a hint.
- In a car you do not know, look inside the flap over your filler or at the cap before the first fill: plenty of motors state the fuel there.
- One of each in the home? Label the key to the diesel — a coloured fob, a sticker — because meaning to remember is not enough.
- "Diesel", out loud, before you lift the nozzle — each time a new or hired car needs its first tank. It seems daft. It does the trick.
- Thinking about something else is when this becomes an easy mistake to make, and so put your phone away then keep your mind on the petrol pump.
- Add-on devices are available for motors without one, and some diesels come with a filler that will not take a petrol nozzle. Helpful — but a backstop at best, never a reason to stop checking the label.
- Stop as soon as you realise. Less petrol in that tank means a weaker mix. It doesn't change what to do next, which is still not to fire it up.
Petrol already in a diesel in New Town? Start here
In that case, there's only a short order of things. Starting it is out, and so is turning on your ignition. If you are still on the forecourt — GG On the move or anywhere else — ask the attendants to help you push it clear of the pump. Ring 0333 366 0103 next, with three facts — your fuel, the approximate quantity, and if it has run.
Say so if it was AdBlue instead of petrol: it's a different fault, with its own page for New Town, because AdBlue brings corrosion and deposits instead of lost lubrication.
Why one petrol in a diesel job around New Town costs more than another
There is no fair single quote for this, since the four situations above are four different jobs. Mostly, the cost moves with which situation you're in. Where the car is matters too, and whether a technician can safely reach it, after the proportion of petrol to what the tank holds.
That's why our engineers ask three queries before pricing instead of after: what was put in, how much, and if it has run. Those replies are what turn a range into one firm number.
About New Town and its setting
New Town is a suburban area in Bedfordshire, situated approximately 28 miles north of London and 8.8 miles southeast of St Albans. New Town sits at an elevation of around 148 metres, in a gently sloping landscape of inland Eastern England. New Town is characterised by a high proportion of flat dwellings, and is located near other residential areas such as Park Town and Farley Hill.
New Town and Bedfordshire: where our fuel drain cover runs
Petrol in diesel call-outs around New Town — part of the LU postcode area — go to vans that also cover the spots about it, Park Town, Luton and Farley Hill among them. A forecourt, a supermarket car park, a lay-by or your own drive are all spots our technicians work, and your car doesn't need to come to us.
Still at the pump in New Town?
Then, you could not be in a better place. Keep it turned off, then ring.