Should You Worry? Petrol in a Diesel Car in Chippenham
Less than you probably are, if it hasn't been started. Till your ignition primes the pump, your starter turns, or the vehicle is driven, petrol in a diesel tank simply rests there and does no harm. Which makes the truthful reply to that first Chippenham query — "have I ruined it?" — usually no. To leave it like that, ring Petrol in Diesel and leave the engine alone. 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.
Your engine and petrol in a diesel: what happens
Diesel does two jobs on its way through an engine. It lubricates first, and after that does it burn. Extremely fine clearances are built into the fuel injectors and the high-pressure pump, and just your diesel running through keeps those surfaces from grinding together.
Of these two tasks, petrol handles the first badly and the second never. The knocking comes from petrol being designed not to ignite when compressed, which is exactly the opposite of what a diesel needs. On top of that it is runnier than diesel, it strips out the protection the system hinges on, and any pump running on such a mix is wearing itself.
Put those together and the shape of the trouble is plain. Not contact but circulation is what causes the harm. Petrol in a tank is a fuel fault. A pump that has been labouring on that petrol is the start of a mechanical one, and whatever a worn pump sheds travels on with the fuel to your injectors further on.
Four scenarios our technicians see around Chippenham: how bad is petrol in a diesel?
Fuelled up, not once started. The best case there is. That petrol is in your tank and just the tank, and the job is a drain and a flush where the vehicle stands. This is the one scenario that can only really happen on a forecourt, because anywhere else the vehicle has been driven to get there.
A moment's running, or merely the ignition on. Your system has been bled, and so petrol has left your tank and reached the filter and the lines. Drain, flush, see to your filter: still usually easy.
Your pump has spent a few miles on weakened fuel — that is what driving it does. Tank, lines, filter, then clean fuel put through the whole system: that is this work, and the way the vehicle was driven counts as much as the miles. Driving the children to Ivy Lane Primary School is one kind of trip. A run as far as Bath, under 15 miles away, is a very different job. So is any mileage on the M4, under 5 miles from Chippenham, where the engine has been labouring hard throughout.
Rattling, a lumpy idle, smoke, a throttle gone soft: driven until it complained. The fuel isn't acting like diesel any more, and your engine is saying so. Whether it is the verge on Market Place, a lay-by or a side road, stop there and leave it. Long-term damage is very unusual if a car is stopped soon, and the fuel drain and flush that still come first deal with it.
What Chippenham 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'll be fine" — a myth. It will not. A bigger tank of the same mix is all it gives, since topping up takes out nothing. The idea behind that guidance — that diesel fuel systems accept petrol by percentage — is wrong.
If anything, the reverse is true. Myth: "A modern diesel can cope with a bit of petrol." Lubrication matters more on current diesels, not less, because their fuel runs through finer parts at higher pressure.
This is the one that fools drivers. Myth: "If it starts and drives, there is no damage done." The driver of a petrol motor fed diesel normally stops, since it will not run, and the damage stops there. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually will; meanwhile your pump grinds. Being able to run is not the same as being fine.
Myth: "Add some two-stroke oil and drive the car home." It is an old workaround for a different fault. The petrol is still inside that tank afterwards, and what it has diluted is not put back.
"Drain it yourself and you are sorted" — a myth, since after it has been running some petrol lies in your filter and lines, waiting to go straight back through your pump at your next start. It is also truly risky to drain petrol into a can at the kerbside.
How does petrol in a diesel happen?
On purpose? Never. Through carelessness? Rarely, if ever. The forecourt makes it simple: the petrol nozzle is the narrower of the two, and it slides into a diesel filler with almost no resistance, whilst a diesel nozzle generally won't go into a petrol motor at all. So the slip runs one way.
Routine and the vehicle falling out of step is when it happens. Courtesy car, hire car, or a motor that is brand new. Two vehicles on one drive, one petrol, one diesel. A forecourt you know, but with its pumps arranged differently. A rushed fill en route to the nearest station with a train to catch. Precisely the moment it takes place: after years of driving petrol, someone fills a diesel Volkswagen Golf for the first time. Add a back seat full of children, a phone call or rain, and the hand takes over.
Next time you fill up in Chippenham: avoiding petrol in a diesel
- Check the petrol pump, not the colour. In the UK unleaded handles are generally green and diesel black, but not on each forecourt. The label is what matters.
- The first fill in a new motor is the time to check the filler flap — inside it, or on the cap, many cars state the fuel they take.
- Good intentions count for less than a sticker or a fob in a bright colour on the diesel's key when a house has one of each. So mark it.
- Before the nozzle leaves the pump the first time you fill a hired or new motor, say "diesel" aloud. Silly, perhaps, but it does the trick.
- Put the phone away. This is an easy mistake to make whilst you are thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler designed to refuse a petrol nozzle, and aftermarket devices exist for the rest. Count it as a backstop, and keep reading the pump.
- As soon as you notice, stop: less petrol in your tank means a thinner blend. What to do next does not change, though — still don't start the car.
Petrol already in a diesel around Chippenham? Begin here
Then the order of things is short. Don't start the vehicle, and don't turn your ignition on. Ask the attendants to help you roll it clear of the pump if you are still at the forecourt, whether that is Sovereign Service Station or somewhere else. Then ring 0333 366 0103 and tell us what was put in, roughly how much, and whether it has run.
Corrosion and deposits form the trouble with AdBlue, whereas petrol means lost protection. So if it was AdBlue, say so — and see its own Chippenham page.
Chippenham petrol in a diesel tasks: why one costs more than another
Four different tasks sit behind the four scenarios above — which is why there's no honest single quote. Mostly, the cost moves with which situation you are in. After that it is the share — how much petrol went in against how much the tank takes — and then where the vehicle is and whether our van can get to it safely.
Ahead of any quote, not after, come three questions: the fuel that was put in, its quantity, and whether it has run. That is why. Given those answers, you get a straight figure rather than a range.
About Chippenham and its setting
Chippenham is a town situated in a riverside location in Wiltshire, England, with a history dating back to before the Roman era. Chippenham has developed around a crossing point on the River Avon, and its strategic position has contributed to its growth over the centuries. The town's proximity to the Cotswolds and its transport links have also played a significant role in its development. Chippenham is a notable settlement in the region, with a rich history and natural surroundings.
Chippenham and Wiltshire: where our fuel drain cover runs
Petrol in diesel call-outs in Chippenham — part of the SN postcode area — go to teams that likewise cover the locations round it, Gladstone Parade, Peckingell and Pewsham included. Our engineers drain wherever your car is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
Still at the pump around Chippenham?
Nothing beats it: that's where you now are. Switched off it stays; then phone.