Park Royal: Petrol in a Diesel Car? How Worried to Be
Far less than you likely are, if it has not been started. Until your ignition primes your pump, your starter cranks, or your vehicle is driven, petrol in a diesel tank simply sits there and does nothing. Which means the truthful reply to that first Park Royal query — "have I wrecked it?" — usually no. Petrol in Diesel is who to ring, with the engine kept off, so it stays that way. The rest of this page covers 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 again.
What petrol in a diesel does to the motor
On its way through a motor, diesel has two tasks. Before it combusts, it lubricates — and then it burns. The high-pressure fuel pump and the injectors are made to extremely fine clearances, and the diesel passing through them is what stops those surfaces from wearing down against each other.
The second job petrol doesn't do at all, and the first it does poorly. It's runnier than diesel and removes the lubrication the fuel system rests on, and so a pump running on a petrol mix is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That is where the knocking comes from.
Seen together, they show the shape the problem takes. It is circulation that causes the harm, not contact. Petrol in the tank is a fuel issue. Once the pump has been running on that petrol, a mechanical problem has started: whatever is shed by a pump that is grinding is carried onward to the injectors with the fuel.
Petrol in a diesel in Park Royal: how bad is it? Four cases
Fuelled up, never started. The best case there is. The petrol is in your tank and only the tank, and the job is a drain and a flush where your car sits. This is the one situation that can only really occur at a forecourt, because anywhere else the vehicle has been driven to get there.
Started for a moment, or just the ignition on. Petrol has left that tank and got to your filter and the lines, because the fuel system has been bled. Drain, flush, see to the fuel filter: still normally simple.
Your pump has spent a couple of miles on diluted fuel — that is what driving it does. Distance is only half of it; how hard it was driven counts equally. Either way the work includes that tank, your lines, the fuel filter and clean fuel through the entire circuit. The school run to West Twyford Primary School is one matter. Driving as far as Westminster, under 10 miles away, makes a very different task — as does any distance on the M4, under 3 miles from Park Royal, with the motor labouring hard the whole time.
It complained, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone lumpy. That's the engine telling you its fuel no longer is acting like diesel. Leave it where it stops: a lay-by, a side street, the verge on Rainsford Road. Long-term damage is very uncommon when a car is stopped soon, and the fuel drain and flush that still go first sort it out.
What Park Royal drivers get told about petrol in a diesel — and the myths in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Topping up removes nothing; it gives you a bigger tank of the same mix. Percentage is not how a diesel fuel system copes with petrol, whatever that advice assumes.
Not so: a modern diesel copes with a bit of petrol. Rather, the reverse. Lubrication matters more on modern diesels, not less, because their fuel runs through more precise parts at higher pressure.
This is the one that fools motorists. Myth: "If it starts and drives, there's no damage done." A petrol motor fed diesel generally won't run, so the driver stops and the damage stops with them. Feed petrol to a diesel and it generally fires up, idles and pulls away like nothing has happened — all while its pump wears. Being able to run is not the same as being fine.
Myth: a two-stroke additive lets you to drive home. It is an old workaround, meant for another fault. None of what petrol diluted gets put back by it — and afterwards, the tank still holds the petrol.
If your engine has run, part of the petrol sits in your filter and the lines, not the tank — and the next start pulls it straight back through your pump. So the myth "drain that tank yourself and you're sorted" does not stand up. Also, a can of petrol drained by the roadside is truly hazardous.
Why petrol in a diesel occurs so easily
No one does it on purpose, and it's rarely carelessness. The petrol nozzle is the narrower of the two and slips into a diesel filler with almost no resistance; a diesel nozzle generally will not go into a petrol vehicle at all. The forecourt makes it simple, and the mistake runs one way.
When routine and the vehicle stop matching, it takes place. Courtesy car, hire car, or a car that's new. A household with one petrol and one diesel on the driveway. A familiar forecourt with the pumps in a different order. A rushed fill on the way to Acton Main Line with a train to catch. Exactly the moment it occurs: after years of driving petrol, someone fills a diesel Renault Clio for the first time. With rain, a call coming in, or children to deal with, your hand just does what it has always done.
Next time you fill up in Park Royal: avoiding petrol in a diesel
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most usually do. Read the petrol pump's label; the colour is just a clue.
- The first fill in a strange vehicle is the time to check your filler flap — inside it, or on the cap, plenty of vehicles state the fuel to use.
- One of each in the household? Mark the key to the diesel — a coloured fob, a sticker — because meaning to remember isn't enough.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the pump. It seems silly and it works.
- Thinking about something else is when this becomes an easy mistake to make, and so tuck your phone away then keep your mind on the pump.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler designed to block a petrol nozzle, and add-on devices exist for vehicles without one. They are a backstop, not a reason to stop checking the petrol pump.
- Stop as soon as you notice. Less petrol inside that tank means a weaker mix. It doesn't change what to do next, which is still not to start it.
Petrol already in a diesel in Park Royal? Start here
Short and simple, then, is the order of things. Starting it is out, and so is turning on your ignition. If you are still at the forecourt — BP or anywhere else — ask the attendants to help you roll it away from the pump. What went in, roughly how much, and if it's run: tell us that when you call 0333 366 0103.
Say so if it was AdBlue instead of petrol: it's a separate issue, with its own page for Park Royal, since AdBlue brings corrosion and deposits instead of lost lubrication.
One petrol in a diesel task in Park Royal costs more than another. Why?
The four situations above are four separate tasks, so no single quote for this would be honest. Mostly, the cost moves with which situation you're in. Where the car is counts too, and whether a technician can safely reach it, after the proportion of petrol to what that tank holds.
What was put in, how much, and if it has run — three questions we ask before costing, not after, for exactly that reason. The replies change a range into a straight figure.
About Park Royal and where it is
Park Royal is a locality in northwest London, situated on the River Brent at an elevation of around 37 metres. Park Royal lies close to the Grand Union Canal and is near several other localities, including North Acton, Lower Place, and West Acton. Park Royal is characterized by its predominantly flat-type housing and is located approximately 6.7 miles from central London.
Park Royal and Greater London: where our fuel drain cover runs
Petrol in diesel jobs around Park Royal — part of the NW postcode area — go to teams that also cover the places round it, North Acton, Lower Place and West Acton included. Our engineers drain where your car is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
Park Royal: still at the petrol pump?
No position is better: that is where you now are. Call, and leave it turned off.