Marsham: Petrol in a Diesel Car? How Worried to Be
Far less than you probably are, if it has not been started. Until the ignition primes your pump, the starter turns, or the vehicle is driven, petrol in a diesel tank simply sits there and does nothing. Which makes the honest reply to that first Marsham question — "have I ruined it?" — normally no. Keep it like that: leave the motor off then phone Petrol in Diesel. The rest of this page sets out what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
Inside the engine: what petrol in a diesel does
Passing through an engine, diesel does two things at once. Oiling comes before burning; it does both. Extremely fine gaps are built into the injectors and your high-pressure pump, and only your diesel running 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 away the protection a fuel system needs, leaving a pump running on the mixture wearing itself. It is equally made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the knocking.
The shape of the problem is clear when you put those together. Contact does not do the harm — circulation does. Petrol in the tank is a fuel problem. The start of a mechanical one is a pump that has been running on that petrol — and whatever a worn pump sheds moves on with the fuel to the fuel injectors beyond it.
Marsham, petrol in a diesel: four situations, from mild to significant
Filled up, and not started: no case is better. Just that tank has petrol in it, so the task is emptying the tank and cleaning the fuel system where the car stands. This situation can only truly occur on a forecourt: anywhere else, the vehicle got there by being driven.
Started for a moment, or just your ignition on. Petrol has left that tank and reached your filter and the lines, since the fuel system has been primed. That is usually still an easy task — a drain, a flush, and your filter seen to.
Those few miles driven were the pump labouring on fuel thinned by petrol the whole way. Tank, lines, filter, then clean fuel put through the whole system: that is this work, and the way your car was driven matters as much as the miles. The school run to John of Gaunt Infant and Nursery School is one matter. Very different once more: a trip to Norwich, under 10 miles away, or some mileage on the M11, over 50 miles from Marsham, where your engine never stopped working hard.
Knocking, an uneven idle, smoke, a throttle gone soft: driven till it complained. The fuel isn't acting like diesel any more, and the motor is telling you. Whether it's the verge on Wathen Way, a lay-by or a side street, stop where you are then leave it. The drain and flush still go first, and they take care of it: when a vehicle is pulled over quickly, long-term damage is very rare.
Stories Marsham people hear about petrol in a diesel
Myth: topping up to full with diesel makes it fine. It does not. Topping up removes nothing; it gives you a bigger tank of the same mix. A diesel fuel system does not tolerate petrol by percentage in the way that guidance assumes.
If anything, the reverse is true. Myth: "A newer diesel can cope with a bit of petrol." Protection matters more on current diesels, not less, since their fuel runs through more precise parts at higher pressure.
"It starts, it drives, so no harm done" — the myth that trips up more motorists than any other. Feed diesel to a petrol engine and it generally won't run, so the motorist stops — 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 the pump grinds. Running is not the same as fine.
An outdated fix for a separate problem lies behind this one. Myth: "Add some two-stroke oil and drive it home." What petrol has weakened remains diluted, and that petrol remains inside the tank anyway.
Myth: "Drain that tank yourself and you're sorted." After your 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 straight back through your pump at your next start. Emptying petrol into a can by the kerbside is also truly dangerous.
Petrol in a diesel: how does it take place?
Carelessness is rarely the cause, and nobody means to do it. 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 car at all. The forecourt makes it simple, and the slip runs one way.
When routine and the vehicle stop matching, it takes place. Any car that is new to you — hired, on loan as a courtesy car, or brand new. Two cars on one drive, one petrol, one diesel. Your usual forecourt, its pumps now in a different order. A hurried fill on the way to Worstead with a train to catch. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is precisely the moment it occurs. Throw in rain, a phone call or a back seat full of children, and your hand repeats what it has always done.
Next time you fill up around Marsham: avoiding petrol in a diesel
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, even if most usually do. Read the petrol pump's label; the colour is just a clue.
- In a car you don't know, look inside the flap over the filler or at the cap before the first fill: many motors print the fuel type there.
- A coloured fob or a sticker on the diesel's key achieves more than any amount of meaning to remember, in a house with one of each.
- "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.
- Put the phone away. This is an easy mistake to make whilst you're thinking about something else.
- Add-on devices exist for motors without one, and some diesels are built with a filler that won't take a petrol nozzle. Helpful — but a backstop at best, never a reason to stop checking the label.
- The moment you realise, stop: less petrol inside your tank means a weaker mixture. What to do next does not change, though — still don't crank it.
Already put petrol in a diesel around Marsham?
Then, there is just a short order of things. Leave it unstarted, with the ignition switched off as well. The attendants at the forecourt — whether at BP itself or wherever you filled up — will normally help push it away from the pump if you ask. Ring 0333 366 0103 next, with three answers — your fuel, the rough quantity, and whether it's run.
Corrosion and deposits are the issue with AdBlue, whereas petrol means lost lubrication. So if it was AdBlue, say so — and read its own Marsham page.
Why one petrol in a diesel task around Marsham costs more than another
There's no fair single quote for this, since the four situations above are four different jobs. The situation itself does most of the work of moving the cost. Where the car is counts too, and whether a technician can safely reach it, after the proportion of petrol to what your tank takes.
What went in, how much, and if it has run — three questions our technicians ask before pricing, not after, for exactly that reason. Given those answers, you get a straight figure instead of a range.
About Marsham and its setting
Marsham is a small village in Norfolk, situated on the banks of a river at an elevation of 31 metres. Marsham lies approximately 9.9 miles northwest of Norwich and 105 miles northeast of London. Marsham has a mix of housing types, but semi-detached homes are predominant in the village. Marsham is close to other nearby places, including Cambridge and Little London.
Across Norfolk and around Marsham: fuel drain cover
Petrol in diesel jobs around Marsham — part of the NR postcode area — go to vans that likewise cover the spots around it, Cambridge, Little London and Westgate Street included. You need not bring the vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all spots we drain.
At the pump around Marsham, still?
In that case, you could not be in a better spot. Keep it off. Phone.