Should You Worry? Petrol in a Diesel Car in Newmarket
Unstarted? Then less anxious than you probably feel. Everyone around Newmarket starts with "have I wrecked it?", and the fair answer is generally no: petrol left inside that tank of a diesel remains harmless till priming, cranking or driving draws it into the fuel system. Petrol in Diesel is who to ring, with the engine left 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 again: that's the rest of this page.
The motor and petrol in a diesel: what goes on
Passing through an engine, diesel does two jobs at the same time. Lubricating comes before burning; it does both. The high-pressure fuel pump and the fuel injectors are built to very fine gaps, and the diesel passing through them is what stops those surfaces from grinding against each other.
Of those two jobs, petrol manages the first badly and the second not at all. Being less viscous than diesel, petrol strips away the protection a fuel system needs, leaving a pump running on the blend wearing itself. It's equally made to resist igniting under compression — the reverse of what a diesel needs — which is why you get the knocking.
Seen together, they show the shape the issue takes. Not contact but movement is what does the damage. Petrol in the tank is a fuel fault. Whatever a worn pump sheds travels on, borne by the fuel, into the fuel injectors downstream, which is why a pump that has been working on the petrol is where a mechanical problem starts.
How serious is petrol in a diesel? Four situations our technicians see in Newmarket
The best case there is: filled up, never started. Being at a forecourt is what makes this the case: elsewhere, the car has been driven there to begin with. With that petrol held inside the tank alone, it is drained and cleaned right where it stands, and nothing more is needed.
Your ignition switched on, or a brief start. Petrol has come out of your tank and got to your filter and your lines, because the fuel system has been bled. Drain, flush, see to your filter: still usually simple.
Your pump has worked a few miles on diluted fuel — that's what driving the vehicle meant. How hard your car was driven counts as much as how far, and the work takes in the tank, the lines, the filter and clean fuel through the whole system. Short trips, like the school run to Nailsworth Church of England Primary School, are one matter. A run as far as Gloucester, under 15 miles away, is a very different task. So is any distance on the M5, under 10 miles from Newmarket, where your engine has been working hard the whole time.
It complained, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone ragged. That's the motor telling you its fuel no longer is acting like diesel. Pull up wherever you are — the verge on Seven Acres Road, a lay-by, a side street — then leave the car there. A vehicle pulled over early very seldom has permanent damage, as the fuel drain and the flush, which still come first, deal with it.
What Newmarket people get told about petrol in a diesel — and the myths in it
"Top it up the rest of the way with diesel and it will 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 idea behind the advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
If anything, the reverse is true. Myth: "A current diesel can cope with a bit of petrol." A newer diesel sends its fuel through finer components at higher pressure, which makes the lubrication count more, not less.
"It starts, it drives, and so no harm done" — the myth that trips up most drivers than any other. The driver of a petrol engine fed diesel usually stops, since it will not run, and the harm stops with them. Feed petrol to a diesel and it normally starts, ticks over and pulls away as if nothing happened — all the while its pump is wearing. Running isn't the same as fine.
Myth: "Add some two-stroke oil and drive it home." It's an old fix for a different problem. It does not put back what petrol has thinned, and the petrol is still inside your tank later.
Myth: "Drain the tank yourself and you are sorted." Once the motor has run, some of that petrol is no longer in that tank: it's in your filter and the lines, and it goes straight back through your pump on your next start. Besides, petrol cleared into a can by the road is genuinely hazardous.
How petrol ends up: petrol in a diesel
On purpose? Never. Through carelessness? Rarely, if ever. The petrol nozzle is the slimmer of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol motor at all. The forecourt makes it simple, and the error runs one way.
Routine and the car falling out of step is how it occurs. Hire cars, courtesy cars, and cars that are new to you. A household with one petrol and one diesel on the drive. A forecourt you know, but with its pumps arranged differently. Filling up in a rush en route to Stroud, with a train to catch. Exactly the moment it takes place: after years of driving petrol, a driver fills a diesel Renault Megane for the first time. Add a back seat full of children, a phone call or rain, and the hand wins.
Avoiding petrol in a diesel next time you fill up in Newmarket
- A green handle for unleaded and black for diesel is usual in the UK — but not on each forecourt. Go by the label on the petrol pump, not the colour.
- Plenty of motors state the fuel inside your filler flap or on the cap, so check there on your first fill in any vehicle you don't know.
- Mark the key. In a house with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the pump. It sounds daft and it works.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck your phone away.
- Some diesels have a filler built 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 reading the petrol pump.
- Spotting it halfway? Stop there and then. A weaker mix follows from less petrol inside that tank, but your next stage remains the same: don't fire it up.
Newmarket: already put petrol in a diesel?
Then the order of things is brief. Do not fire it up, and don't switch your ignition on. If you are still on the forecourt — Shell or anywhere else — ask the staff to help you roll it away from the pump. What was put in, about how much, and whether it has run: tell us those when you phone 0333 366 0103.
Corrosion and deposits form the problem with AdBlue, where petrol brings lost lubrication. So if it was AdBlue, say so — and see its own Newmarket page.
What makes one Newmarket petrol in a diesel task cost more than the next
The four situations above are four separate tasks, so no single quote for this would be fair. The situation itself does most of the work of moving the cost. The share counts next, meaning how much of your tank is petrol, followed by the position of the car and whether reaching it is safe for our van.
What was put in, how much, and whether it has run — three queries our engineers ask before quoting, not after, for exactly that reason. Given those replies, you get a straight figure instead of a range.
About Newmarket itself
Newmarket is a suburban area in Gloucestershire, situated on the riverside at an elevation of around 105 metres. Newmarket lies near the cities of Gloucester and the surrounding villages of Shortwood and Forest Green. Newmarket has a population of approximately 3310 people, predominantly living in semi-detached housing. Newmarket is located about 11.7 miles from Gloucester and 91.3 miles from London.
Fuel drain cover in Newmarket and across Gloucestershire
The vans answering petrol in diesel jobs in Newmarket, in the GL postcode area, also work the spots around it, Shortwood, Worley and Forest Green included. No need to bring your car to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all spots we drain.
Still at the pump around Newmarket?
Then, you couldn't be in a better position. Switched off it remains; then ring.