How Worried Should You Be? Petrol in a Diesel Car in Fox Milne
Far less than you probably are, provided it hasn't been started. Petrol sitting in a diesel tank does nothing to your engine until something draws it through your fuel system — your ignition priming your pump, the starter, or driving on its own. So the truthful answer to the first question everyone in Fox Milne asks, "have I ruined it?", is normally no. Petrol in Diesel is who to call, with your engine left off, so it stays that way. Further down, you will find what petrol really does inside a diesel, how far it may have got, and how to stop it happening to you a second time.
What petrol in a diesel does to the motor
Passing through a motor, diesel does two things at the same time. Before it ignites, it lubricates — and then it burns. The high-pressure pump and the injectors are designed to extremely fine clearances, and the diesel passing through them is what keeps those surfaces from wearing against one another.
Poorly at the first, not at all at the second: that is petrol. A pump working on a petrol mixture is wearing itself out, since petrol is thinner than diesel and strips out the protection the fuel system depends on. Petrol is also made to resist igniting under compression — the opposite of what a diesel wants from its fuel — and that is where any rattling starts.
Taken together, they show what shape the trouble takes. Not contact but movement is what does the damage. Petrol in the tank is a fuel issue. A pump that has been labouring on that petrol is the start of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the fuel injectors downstream.
Four scenarios we see in Fox Milne: how bad is petrol in a diesel?
Filled up, not once started. The best case there can be. Being at a forecourt is what makes this possible: elsewhere, the vehicle has been driven there to begin with. With that petrol kept inside that tank alone, it's cleared and flushed on the spot, and nothing more is needed.
A brief spell of running, or just your ignition on. Petrol has left your tank and reached the fuel filter and the fuel lines, since the fuel system has been primed. That is usually still an easy job — a drain, a flush, and your filter dealt with.
Your pump now worked a few miles on weakened fuel — that's what driving it does. Distance is only half of that; how hard it was driven counts equally. Either way this work includes that tank, the fuel lines, the filter and fresh fuel through the whole circuit. A school run to Middleton Primary School is one matter. A run as far as Milton Keynes, under 3 miles away, is a very different task. So is any mileage on the M1, under a mile from Fox Milne, where the motor has been labouring hard throughout.
It complained, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone lumpy. What you are hearing is your engine reporting fuel that no longer behaves like diesel. Stop on the spot — on the verge on Northfield Drive, at the kerb, down a side road — and don't move it again. Lasting damage is very uncommon if a car is stopped soon, and the drain and flush-through that still go first take care of it.
What Fox Milne drivers get told about petrol in a diesel — and the myths in it
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Topping up removes nothing; it gives you a bigger tank of the same mix. The idea behind that advice — that diesel fuel systems accept petrol by percentage — is wrong.
If anything, the reverse holds. Myth: "A modern diesel can cope with a bit of petrol." Finer parts and higher pressure are the way a current diesel runs its fuel, and that makes the protection matter more, not less.
This is the one that fools motorists. Myth: "If it starts and drives, there's no damage done." Feed diesel to a petrol motor and it usually won't run, so the driver stops — and the harm 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 wears. A running engine doesn't mean fine.
"A drop of two-stroke oil and drive it home" — a myth, borrowed from a fix from years ago, for a separate issue. The petrol is still in your tank after that, and whatever it has weakened isn't put back.
"Drain it yourself and you are sorted" — a myth, because after it's been running some petrol lies in your filter and lines, ready to go right back through your pump on your next start. Also, a can of petrol drained at the kerbside is truly risky.
Petrol in a diesel: how does it happen?
Nobody does it on purpose, and it is seldom carelessness. The petrol nozzle is the slimmer of the two and slides into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol car at all. The forecourt makes it easy, and the mistake runs one way.
It occurs when routine and your car stop matching. Any car that is new to you — hired, on loan as a courtesy car, or just bought. One petrol and one diesel on the drive of the same household. Your ordinary forecourt, its pumps suddenly in a different order. A rushed fill en route to Milton Keynes Central with a train to catch. Precisely the moment it occurs: after years of driving petrol, a driver fills a diesel Volkswagen Tiguan for the first time. With rain, a call arriving, or a car full of children to deal with, the hand simply does what it has always done.
Preventing petrol in a diesel next time you fill up around Fox Milne
- A green handle for unleaded and black for diesel is usual in the UK — but not on every forecourt. Trust the label on the petrol pump, not the colour.
- In a vehicle you do not know, look inside the flap over your filler or at the cap before the first fill: plenty of vehicles print the fuel type there.
- One of each in the home? Mark the key to your diesel — a bright fob, a sticker — because intending to remember isn't enough.
- "Diesel", out loud, before you lift the nozzle — each time a new or hired car needs its first tank. It seems silly. It works.
- Tuck the phone away. This is an easy mistake to make while you are thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler built to refuse a petrol nozzle, and aftermarket devices exist for the remainder. Treat it as a safety net, then keep checking the petrol pump.
- Stop as soon as you notice. Less petrol inside that tank means a thinner mixture. It doesn't change what to do next, which is still not to start it.
Fox Milne: already put petrol in a diesel?
Short and simple, then, is the order of things. Never crank it, and don't switch the ignition on. If you're still on the forecourt — Shell or anywhere else — ask the staff to help you push it away from the pump. Then ring 0333 366 0103 and tell us what was put in, about how much, and whether it has run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost lubrication, make it a separate issue — Fox Milne has a page just for it.
Why one petrol in a diesel task around Fox Milne costs more than another
There's no honest single price for this, since the four situations above are four separate jobs. What shifts the cost is chiefly which of them you're in. Where the car is counts too, and whether a van can safely reach it, after the share of petrol to what that tank takes.
Three queries come first, before any quote, rather than after — what got in, how much, has it run — and that is the reason. The answers change a range into a straight figure.
About Fox Milne itself
Fox Milne is a suburban area situated on the outskirts of Milton Keynes in Buckinghamshire, with a lakeside setting at an elevation of around 66 metres. Fox Milne is characterized by its predominantly detached housing stock and is located near other residential areas such as Northfield and Atterbury. Fox Milne has a population of approximately 1254 residents and is within a short distance of Milton Keynes Village. Fox Milne is also relatively close to London, being around 45 miles away.
Fuel drain cover around Fox Milne and across Buckinghamshire
Northfield, Atterbury and Milton Keynes Village are among the spots around Fox Milne that the same vans work, answering petrol in diesel calls across Fox Milne's MK postcode area. We drain wherever your vehicle is — your own drive, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
At the petrol pump around Fox Milne, still?
Then you are in the best position there is. Turned off it remains; then call.