Brentford: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less worried than you probably are. "Have I wrecked it?" is the first thing everyone around Brentford asks, and the honest answer is generally no, because petrol left in a diesel tank harms nothing till it's dragged through the fuel system — by ignition priming, by your starter, or by driving. Petrol in Diesel is who to phone, with the motor kept off, and so it remains that way. What petrol really does to a diesel, how to gauge how far it has gone, and how to keep it from happening again: that's the rest of this page.
The engine and petrol in a diesel: what happens
On its way through an engine, diesel has two tasks. It combusts, and before it ignites it lubricates. Very fine gaps are built into your injectors and the high-pressure pump, and only the diesel running through keeps their surfaces from grinding together.
Poorly at the first, not at all at the second: that is petrol. It is thinner than diesel and takes away the protection your fuel system depends on, so a pump running on a petrol mixture is a pump wearing itself. And petrol is made to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That is where the rattling comes from.
Put these together and the shape of the problem is clear. It's movement that does the harm, not contact. Where that petrol is only inside your tank, it's a fault of fuel, nothing more. Whatever a worn pump sheds goes on, borne by the fuel, into the fuel injectors further along, which is why a pump that has been working on the petrol is where a mechanical fault begins.
Four scenarios we see around Brentford: how serious is petrol in a diesel?
Filled up, and never started: no case is better. At a forecourt, and genuinely only there, that petrol is still limited to that tank — because anywhere else the vehicle was driven to get to it. The task is draining and rinsing on the spot.
Started for a second, or only the ignition on. Once primed, your system has pulled petrol out of that tank as far as the fuel filter and the lines. Still normally easy: drain, flush, and the filter seen to.
Driven a couple of miles. Now the pump has spent those miles working on diluted fuel. The work is the tank, the lines, your filter and clean fuel through the entire system, and how hard the vehicle was driven counts as much as how far. On the school run to St Paul's CofE Primary School, the mileage is small. Any mileage on the M4, under a mile from Brentford, means the motor working hard throughout, and a run to Westminster, under 10 miles away, is a very different task too.
Clattering, a lumpy idle, smoke, a throttle gone soft: driven until it complained. The fuel isn't acting like diesel any more, and your motor is telling you. Stop where you are — on the verge on Brentford High Street, at the kerb, down a side road — and do not move it. Long-term damage is very rare if a vehicle is pulled over soon, and the fuel drain and flush-through that still go first deal with it.
Petrol in a diesel stories Brentford motorists hear
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Topping up removes nothing; it gives you a bigger tank of the same mixture. The assumption behind that guidance — that diesel fuel systems tolerate petrol by percentage — is wrong.
Not so: a current diesel copes with a bit of petrol. If anything, the reverse. Protection matters more on newer diesels, not less, since their fuel passes through more precise parts at higher pressure.
Myth: "If it starts and drives, there's no damage done." This is the one that fools motorists. A petrol engine fed diesel generally won't run, so the driver stops and the damage stops with them. Whilst the pump wears, a diesel fed petrol normally starts, ticks over and drives away as if nothing has happened. Fine and running aren't the same thing.
Myth: "Add some two-stroke oil and drive the vehicle home." It is an outdated workaround for a separate fault. It doesn't put back what petrol has thinned, and that petrol is still in the tank after that.
If your engine has run, part of that petrol sits in the filter and the lines, not that tank — and your next start pulls it right back through your pump. So the myth "drain your tank yourself and you're sorted" does not hold. And, a can of petrol drained by the kerbside is genuinely dangerous.
How it happens: petrol in a diesel
It is seldom carelessness, and no one does it on purpose. One way only, because of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, while the diesel one mostly will not fit a petrol motor. That is how the forecourt makes it easy.
When habit and the car stop matching, it occurs. Courtesy car, hire car, or a car that's brand new. One petrol and one diesel on the driveway of the same household. Your usual forecourt, its pumps now in a different order. Racing for a train outside the nearest station and filling up en route. Exactly the moment it occurs: after years of driving petrol, someone fills a diesel Volkswagen Golf for the first time. The hand does what it has always done when you add rain, a phone call or a back seat full of kids.
Next time you fill up around Brentford: preventing petrol in a diesel
- A green handle for unleaded and black for diesel is normal in the UK — yet not on every forecourt. Go by the label on the pump, not the colour.
- Inspect your filler flap. Many cars state the fuel inside the flap or on the cap. Look at it on the first fill in a car you don't know.
- Good intentions count for less than a sticker or a fob in a bright colour on your diesel's key if a house has one of each. So mark it.
- Before the nozzle leaves the petrol pump the first time you fill a hired or new car, say "diesel" aloud. Daft, yes, yet it works.
- Mistakes like this are easy to make whilst your mind is on something else, and so the phone goes away.
- Add-on devices are available for vehicles without one, and some diesels come with a filler that will not accept a petrol nozzle. Useful — but a safety net only, never a reason to stop checking the label.
- The moment you notice, stop: less petrol inside your tank makes a weaker mix. What to do next doesn't change, though — still don't crank it.
Brentford: already put petrol in a diesel?
Short and simple, then, is the order of things. Do not fire it up, and don't turn the ignition on. The staff at the forecourt — whether at Esso itself or wherever you filled up — will usually help roll it away from the petrol pump if you ask. Phone 0333 366 0103 next, with three answers — your fuel, the approximate volume, and if it's run.
Corrosion and deposits are the problem with AdBlue, where petrol means lost lubrication. So if it was AdBlue, say so — and read its own Brentford page.
Why one petrol in a diesel task in Brentford costs more than another
The four scenarios above are four different jobs, so no single quote for this would be honest. Chiefly, the cost moves with which one you're in. Next it's the ratio — how much petrol was put in against how much the tank takes — and after that where the vehicle is and whether a van can reach it safely.
Ahead of any quote, not after, come three questions: your fuel that was put in, the quantity, and if it has run. That is why. A range turns into a straight figure when those replies are in.
About Brentford
Brentford is a locality in west London, situated on the River Thames and adjacent to the Grand Union Canal, with nearby lakes and waterways. Brentford sits at a low elevation of around 13 metres, close to the neighbouring areas of Kew and Strand on the Green. Brentford is characterized by its predominantly flat housing stock, reflecting its urban setting within the Greater London area. Brentford is also near Brentford End, a smaller area within the locality.
Across Greater London and in Brentford: fuel drain cover
Our vans answering petrol in diesel jobs around Brentford, in the TW postcode area, also work the places around it, Brentford End, Kew and Strand on the Green included. Our technicians drain where your vehicle is — your own drive, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
Still at the petrol pump around Brentford?
No position is better: that's where you are. Phone, and keep it turned off.