Seaforth: Petrol in a Diesel Car? How Worried to Be
If it has not been started, you can worry less than you probably are. Until your ignition primes your pump, your starter cranks, or the vehicle is driven, petrol in a diesel tank just rests there and does nothing. Which means the truthful reply to the first Seaforth query — "have I ruined it?" — usually no. Keep it that way: leave the engine off then ring Petrol in Diesel. The remainder of this page explains what petrol really does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you a second time.
What petrol in a diesel does to the engine
On its way through a motor, diesel does two tasks. It protects first, and after that does it burn. Very fine gaps are built into the injectors and your high-pressure pump, and just the diesel flowing through stops those surfaces grinding together.
Badly at the first, not at all at the second: that is petrol. Being less viscous than diesel, petrol strips out the lubrication a fuel system needs, so a pump running on that mixture wearing itself. It's equally made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the clattering.
The shape of the problem is plain once you put those together. Contact doesn't do the damage — circulation does. Petrol in the tank is a fuel fault. Whatever a worn pump sheds travels on, borne by your fuel, into the fuel injectors downstream, which is why a pump that has worked on the petrol is where a mechanical fault starts.
Four scenarios our engineers see around Seaforth: how serious is petrol in a diesel?
The best case there is: filled up, not once started. The petrol is in that tank and just your tank, and the job is a drain and a flush where the vehicle stands. This is the one situation that can only really take place at a forecourt, since anywhere else the car has been driven to get there.
A brief spell of running, or merely the ignition on. Petrol has come out of your tank and got to the filter and the fuel lines, because the fuel system has been bled. Drain, flush, see to your filter: still normally easy.
Some miles driven, and the pump has spent every one of them running on diluted fuel. Tank, lines, filter, then clean fuel put through the whole system: that is the work, and the way your car was driven matters as much as the miles. On the school run to Rimrose Hope CofE Primary School, the miles is short. A run as far as Liverpool, under 5 miles away, is a very different task. So is any miles on the M57, under 5 miles from Seaforth, where the engine has been working hard throughout.
It complained, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone lumpy. That is the motor telling you its fuel has stopped behaving like diesel. Leave it wherever it has stopped: a lay-by, a side street, the verge on Cambridge Road. A car pulled over quickly very rarely has long-term damage, because the drain and the flush, which still go first, take care of it.
Seaforth drivers and that petrol in a diesel myths they hear
False: topping up to full with diesel makes it fine. It does not. A bigger tank of the same mixture is all you get, since topping up takes out nothing. That advice supposes a diesel fuel system handles petrol by percentage. It does not.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the reverse. Lubrication counts more on modern diesels, not less, since their fuel passes through more precise parts at higher pressure.
One myth that catches drivers out: if it starts and drives, it must be unharmed. A petrol motor fed diesel normally will not run, so the driver stops and the damage stops with them. Whilst the pump wears, a diesel fed petrol usually starts, ticks over and drives away as though nothing has happened. A running engine does not mean fine.
Myth: "Add some two-stroke oil and drive it home." It's an outdated fix for a different issue. What petrol has weakened stays weakened, and that petrol stays in that tank anyway.
The next start draws petrol back round your pump from the fuel lines and the fuel filter, where some of that ends up once your engine has run. That is why a DIY tank drain does not sort it — a myth. Clearing petrol into a can at the roadside is also really risky.
Why petrol in a diesel happens at all
No one does it on purpose, and it's seldom carelessness. A diesel nozzle mostly won't go into a petrol motor, yet the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one mistake straightforward, and only in one direction.
The moment habit stops matching the vehicle is the moment it occurs. Hire cars, courtesy cars, and vehicles that are new to you. A household with one petrol and one diesel on the drive. A familiar forecourt with the pumps in a different order. Filling up in a hurry en route to Waterloo (Merseyside), with a train to catch. Precisely the moment it takes place: after years of driving petrol, a driver fills a diesel Volkswagen Golf for the first time. With rain, a call arriving, or a car full of children to deal with, your hand simply does what it always has.
How to avoid petrol in a diesel at your next fill-up around Seaforth
- Read the pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on every forecourt. The label is what counts.
- Check your filler flap. Plenty of motors state the fuel inside the flap or on the cap. Look at it on your first fill in any vehicle you do not know.
- One of each in the home? Label your key to the diesel — a bright fob, a sticker — since meaning to remember is not enough.
- "Diesel", aloud, before you pick up the nozzle — each time a new or hired car gets its first tank. It sounds daft. It works.
- Mistakes like this are easy to make whilst your mind is on something else, and so your phone goes away.
- Some diesels come with a filler designed to reject a petrol nozzle, and devices you can add exist for vehicles without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop reading the pump.
- The moment you realise, stop: less petrol in the tank means a weaker blend. What to do next does not change, though — still do not crank it.
Petrol already in a diesel around Seaforth? Start here
Then the order of things is short. Starting it is out, and so is switching on your ignition. The attendants on the forecourt — whether at Shell itself or wherever you filled up — will usually help push it clear of the pump if you ask. Next, 0333 366 0103. We will ask what was put in, about how much, and if it's been run.
Corrosion and deposits are the trouble with AdBlue, where petrol brings lost lubrication. So if it was AdBlue, say so — and read its own Seaforth page.
Seaforth petrol in a diesel jobs: why one costs more than another
The four situations above are four different jobs, so no single price for this would be fair. The situation itself does most of the work of moving the cost. After that it is the proportion — how much petrol got in against how much your tank holds — and then where the car is and whether a technician can get to it safely.
What got in, how much, and whether it has run — three queries our engineers ask before pricing, not after, for exactly that reason. A range becomes a straight figure when those answers are in.
About Seaforth and where it is
Seaforth is a coastal suburban area in Merseyside, situated near the mouth of the River Mersey and close to the city of Liverpool. Seaforth has a relatively low elevation of around 10 metres above sea level and is bordered by nearby places such as Crosby and Waterloo. Seaforth is characterized by its semi-detached housing stock and is home to approximately 4735 residents. Seaforth is also near Waterloo Park, a local green space.
Seaforth and Merseyside: where our fuel drain cover reaches
Seaforth waits in the L postcode area, and our vans that answer petrol in diesel jobs there work the spots around it as well — Crosby, Waterloo and Waterloo Park among them. We drain wherever your vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
In Seaforth and still at the petrol pump?
In that case, you couldn't be in a better place. Keep it switched off, and ring.