Should You Worry? Petrol in a Diesel Car in Grendon Underwood
If it has not been started, worry far less than you likely are. Till your ignition primes the pump, the starter cranks, or the car is driven, petrol in a diesel tank simply waits there and does no harm. Which makes the truthful reply to that first Grendon Underwood question — "have I ruined it?" — usually no. To keep the car like that, phone Petrol in Diesel then leave the engine alone. Below, you will find what petrol really does inside a diesel, how far it might have gone, and how to stop it happening to you a second time.
What petrol in a diesel does to the engine
Passing through an engine, diesel does two jobs at the same time. Before it ignites, it protects — and then it burns. Designed to very fine tolerances, your injectors and your pump depend on your diesel moving through them to stop their surfaces wearing against one another.
Of those two jobs, petrol manages the first badly and the second not at all. It is runnier than diesel and strips away the protection your fuel system hinges on, so a pump running on a petrol mix is a pump wearing itself. And petrol is made to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That's where the clattering comes from.
The shape of the trouble is clear when you put those together. The damage is done by circulation, not by contact. Any tank with petrol in it 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's grinding is carried onward to the injectors with your fuel.
Grendon Underwood, petrol in a diesel: four cases, from mild to significant
Fuelled, and not started: no case is better. Being at a forecourt is what makes this the case: elsewhere, the vehicle has been driven there to begin with. With that petrol held in your tank alone, it is drained and purged on the spot, and nothing more is needed.
Ignition on, or started for a moment. The fuel system has been bled, and so petrol has left the tank and reached the fuel filter and your lines. Usually little more than emptying, rinsing and sorting the fuel filter, and so still straightforward.
Some miles driven, and the pump has spent each of them working on diluted fuel. How hard your car was driven matters as much as how far, and this work covers that tank, your lines, the filter and fresh fuel through the whole system. A school run to Grendon Underwood School is one thing. A run as far as Oxford, under 15 miles away, is a very different job. So is any miles on the M40, under 10 miles from Grendon Underwood, where the motor has been running hard the whole time.
Driven till it complained. Knocking, an uneven idle, smoke, a throttle that has gone soft. That is the engine telling you its fuel no longer is acting like diesel. Leave it wherever it stops: a lay-by, a side street, the verge on Bakery Close. The fuel drain and flush-through still come first, and they sort it out: when a car is pulled over soon, permanent damage is very uncommon.
What Grendon Underwood drivers get told about petrol in a diesel — and the myths in it
Myth: topping up to full with diesel makes it fine. It doesn't. Topping up takes out nothing; it gives you a bigger tank of the same mix. A diesel fuel system doesn't accept petrol by percentage in the way that guidance supposes.
"Modern diesels can handle a little petrol" — a myth, and closer to the reverse. Protection counts more on modern diesels, not less, because their fuel passes through finer parts at higher pressure.
"It starts, it drives, so no harm done" — the myth that trips up most drivers than any other. A petrol motor fed diesel generally won't run, and so the driver stops and the damage 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 does not mean fine.
An outdated workaround for a different fault lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." None of what petrol diluted gets put back by it — and afterwards, the tank still contains that petrol.
Myth: "Drain that tank yourself and you are sorted." After the engine has run, some of that petrol is no longer in that tank: it is in the fuel filter and your lines, and it goes right back through the pump at your next start. Draining petrol into a can at the kerbside is also genuinely risky.
Why petrol in a diesel occurs so easily
It's rarely carelessness, and nobody does it on purpose. The forecourt makes it simple: the petrol nozzle is the narrower of the two, and it slips into a diesel filler with almost no resistance, whilst a diesel nozzle generally won't go into a petrol motor at all. So the error runs one way.
Habit and the vehicle falling out of step is how it happens. A new motor, a hire car or a courtesy car. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a familiar forecourt. Racing for a train outside Bicester Village and filling up en route. Precisely the moment it happens: after years of driving petrol, a driver fills a diesel Renault Megane for the first time. With rain, a call arriving, or a car full of children to deal with, your hand just does what it always has.
Next time you fill up in Grendon Underwood: preventing petrol in a diesel
- Check the petrol pump, not the colour. In the UK unleaded handles are usually green and diesel black, yet not on every forecourt. The label is what matters.
- Check your filler flap. Plenty of cars state the fuel type inside the flap or on the cap. Look at it on your first fill in a car you don't know.
- Label the key. In a house with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of intending to remember.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump. It seems daft and it works.
- Put the phone away. This is an easy mistake to make whilst you are thinking about something else.
- Add-on devices are available for motors without one, and some diesels are built with a filler that will not accept a petrol nozzle. Useful — but a safety net only, never a reason to stop checking the label.
- Stop as soon as you notice. Less petrol in your tank makes a weaker blend. It doesn't change what to do next, which is still not to start the vehicle.
Petrol already in a diesel around Grendon Underwood? Begin here
Short and simple, then, is the order of things. Leave it unstarted, with your ignition switched off too. Still at the forecourt, at the nearest petrol station or anywhere else? Ask the attendants to help you roll the vehicle clear of the pump. Ring 0333 366 0103 next, with three answers — your fuel, the approximate quantity, and if it has run.
Say so if it was AdBlue rather than petrol: it is a separate issue, with its own page for Grendon Underwood, since AdBlue brings corrosion and deposits instead of lost protection.
What makes one Grendon Underwood petrol in a diesel task cost more than the next
A fair single quote does not exist here: four situations, four separate jobs. Which of them you are in is chiefly what shifts the cost. Two things come after that: the petrol that got in as a proportion of what that tank takes, then the place the car is in and whether a van can reach it safely.
That's why our technicians ask three queries before quoting rather than after: what got in, how much, and whether it's run. With the answers, you get a straight figure rather than a range.
About Grendon Underwood and where it is
Grendon Underwood is a village in Buckinghamshire, situated near the River Great Ouse at an elevation of around 75 metres. Grendon Underwood lies within the South East region, approximately 45.7 miles from London and 13.8 miles from Oxford. Grendon Underwood has a population of around 727 people, predominantly living in detached houses, and is close to nearby places such as Edgcott and Kingswood.
Across Buckinghamshire and around Grendon Underwood: fuel drain cover
Petrol in diesel call-outs around Grendon Underwood — part of the HP postcode area — go to vans that likewise cover the spots around it, Edgcott, Kingswood and Ham Green among them. Our technicians drain where your vehicle is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
In Grendon Underwood and still at the petrol pump?
In that case, you couldn't be in a better position. Leave it turned off, and ring.