Petrol in a Diesel Car in Cambridge: How Worried Should You Be?
Not started? Then less anxious than you probably are. Petrol sitting in a diesel tank does nothing to your engine till something draws it through the system — the ignition priming the pump, the starter, or the drive on its own. So the honest answer to the first query anyone in Cambridge asks, "have I wrecked it?", is normally no. To keep it like that, phone Petrol in Diesel then leave the motor alone. What petrol really does to a diesel, how to gauge how far it's gone, and how to stop it from happening a second time: that's the remainder of this page.
What petrol in a diesel does to your engine
On its way through an engine, diesel does two jobs. Before it combusts, it protects — then it combusts. Extremely fine tolerances go into your injectors and the high-pressure fuel pump, and just the diesel flowing through stops those surfaces grinding together.
Petrol does the first job badly and the second not at all. It's thinner than diesel and takes away the lubrication the fuel system depends on, and so a pump running on a petrol mix is a pump wearing itself. And petrol is made to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That is where the knocking comes from.
Together, those make the shape of the trouble plain. The harm is done by movement, not by contact. Petrol in a tank is a fuel issue. Whatever a worn pump sheds goes on, borne by the fuel, into your injectors downstream, which is why a pump that has been working on the petrol is where a mechanical issue starts.
How bad is petrol in a diesel? Four situations our engineers see in Cambridge
The best case there can be: filled up, never started. The petrol is in your tank and just the tank, and the job is a drain and a flush where your car sits. This is the one situation that can only truly happen on a forecourt, as anywhere else the vehicle has been driven to get there.
The ignition turned on, or a short start. The fuel system has been primed, and so petrol has left that tank and reached the filter and the fuel lines. Usually little more than clearing, purging and sorting the fuel filter, and so still simple.
Some miles driven, and your pump has spent each 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 the tank, your lines, the fuel filter and fresh fuel through the whole system. Driving the children to Park Street CofE Primary School is one kind of trip. Very different once more: a run to Ely, under 15 miles away, or any miles on the M11, under 3 miles from Cambridge, where your engine kept running hard.
Driven on until it complained — rattling, smoke, an uneven idle, a soft throttle. That's the engine telling you its fuel no longer is acting like diesel. Pull up on the spot — on the verge on Petty Cury, at the kerb, down a side road — and don't move it. The fuel drain and flush-through still go first, and they take care of it: if a vehicle is pulled over quickly, permanent damage is very rare.
Petrol in a diesel myths Cambridge motorists hear
Myth: topping up to full with diesel makes it fine. It does not. Nothing is removed when you top up — the tank simply carries more of the same blend. A diesel fuel system does not accept petrol by percentage in the way that advice presumes.
"Newer diesels can handle a little petrol" — a myth, and closer to the opposite. Finer parts and higher pressure are how a newer diesel runs its fuel, and that makes the lubrication count more, not less.
"It starts, it drives, and so there is no harm" — the myth that trips up more motorists than any other. The motorist of a petrol motor fed diesel normally has no choice but to stop, because it will not run, and the harm stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually does; meanwhile your pump grinds. Being able to run is not the same as being fine.
Myth: "Add some two-stroke oil and drive it home." It's an outdated fix for a different fault. It does not put back what petrol has thinned, and the petrol is still inside the tank later.
The next start draws petrol back round the pump out of the lines and the fuel filter, where some of that ends up after your engine has run. That's why draining the tank yourself doesn't sort it — a myth. Besides, petrol cleared into a can by the road is genuinely hazardous.
How does petrol in a diesel take place?
A careless moment is seldom the cause, and no one means to do it. The forecourt makes it easy: the petrol nozzle is the smaller of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle mostly will not go into a petrol motor at all. So the slip runs one way.
It takes place when routine and the vehicle stop matching. Courtesy car, hire car, or a vehicle that is new. A household with one petrol and one diesel on the driveway. A well-known forecourt with the pumps in a different order. A hurried fill en route to the nearest station with a train to catch. Years of petrol cars behind you, a diesel Volkswagen Golf in front of you on the forecourt for its first tank — that's when. The hand repeats what it has always done once you add rain, a phone call or a back seat full of kids.
Avoiding petrol in a diesel next time you fill up in Cambridge
- The label is what matters, so read the pump instead of the colour: in the UK unleaded handles are normally green and diesel black, yet not on each forecourt.
- Check the filler flap. Many motors state the fuel inside the flap or on the cap. Look at 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, in a home with one of each.
- "Diesel", aloud, before you pick up the nozzle — every time a new or hired car needs its first tank. It sounds silly. It does the trick.
- Mistakes like this are easy to make whilst your mind is on something else, so the phone goes away.
- Add-on devices exist for cars without one, and some diesels come with a filler that will not accept a petrol nozzle. Helpful — but a safety net only, never a reason to stop checking the label.
- The moment you notice, stop: less petrol in your tank makes a weaker blend. What to do next doesn't change, though — still don't start the vehicle.
Petrol already in a diesel around Cambridge? Begin here
The order of things is brief, then. Don't turn the ignition on, and do not start it. The attendants on the forecourt — whether at Shell itself or wherever you filled up — will normally help roll it away from the pump if you ask. Call 0333 366 0103 next, with three answers — the fuel, the approximate volume, and whether it has run.
AdBlue, not petrol? Then tell us. Corrosion and deposits, not lost protection, make it a different issue — Cambridge has a page just for it.
One petrol in a diesel job around Cambridge costs more than another. Why?
Four separate jobs sit behind the four scenarios above — which is why there's no fair single quote. The situation itself does most of the work of moving your cost. After that it's the share — how much petrol was put in against how much that tank takes — and after that where your car is and whether a technician can get to it safely.
Three questions come first, before quoting, instead of after — what got in, how much, has it run — and that is the reason. With those replies, you get a straight figure instead of a range.
About Cambridge
Cambridge is a historic city situated in the east of England, on the banks of the River Cam. It serves as the main town of Cambridgeshire, with a rich past that spans thousands of years. Cambridge has developed from a significant centre of trade and commerce in ancient times to a thriving urban area. The city's scenic riverside setting adds to its charm and character.
Cambridge and Cambridgeshire: where our fuel drain cover reaches
Petrol in diesel calls in Cambridge — part of the CB postcode area — go to teams that also cover the places round it, Newnham Croft, Newnham and Newtown among them. The car doesn't need to move to us: our engineers drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
Cambridge: still at the pump?
No position is better: that is where you are. Leave it switched off, then ring.