Petrol in a Diesel Car in The Holmes: How Worried Should You Be?
Likely less than you are now — as long as no one has started it. Petrol sitting in a diesel tank does nothing to your motor until something draws it through the fuel system — the ignition priming your pump, the starter, or the drive on its own. So the fair answer to the first question everyone in The Holmes asks, "have I ruined it?", is usually no. To keep the car like that, ring Petrol in Diesel then leave the motor alone. Below, this page sets out what petrol really does inside a diesel, how far it may have gone, and how to stop it happening to you a second time.
Inside the engine: what petrol in a diesel really does
Two jobs fall to diesel on its journey round a motor. Before it combusts, it lubricates — and then it ignites. What stops the surfaces inside the high-pressure fuel pump and the injectors from grinding against each other is your diesel flowing through them — they are designed to very fine gaps.
The second task petrol doesn't do at all, and the first it does poorly. The rattling 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 thinner than diesel, it strips away the lubrication the system depends on, and any pump running on such a mixture is wearing itself.
The shape of the trouble is plain once you put those together. It is movement that does the damage, not contact. Where the petrol is only in your tank, it's a problem of fuel, nothing more. Once your pump has been labouring on that petrol, a mechanical fault has begun: whatever is shed by a pump that's wearing is carried downstream to the injectors with your fuel.
How serious is petrol in a diesel? Four situations our engineers see in The Holmes
Filled up, not once started. The best case there can be. Just your tank has petrol in it, so the task is clearing that tank and purging your system where the vehicle sits. This situation can only really happen at a forecourt: anywhere else, the vehicle got there by being driven.
A moment's running, or merely the ignition on. Your system has been bled, and so petrol has left your tank and got to your filter and the fuel lines. That is usually still a simple task — a drain, a flush, and the filter seen to.
Those few miles driven meant your pump running on fuel diluted by petrol throughout. How hard the car was driven counts as much as how far, and the work covers that tank, the lines, the filter and clean fuel through the entire circuit. Short trips, like the school run to Castleward Spencer Academy, are one matter. Any miles on the M1, under 10 miles from The Holmes, means the motor working hard throughout, and a run to Derby, under a mile away, is a very different job too.
It protested, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone uneven. The engine is telling you the fuel is no longer behaving like diesel. Pull up wherever you are — the verge on Morledge, a lay-by, a side street — and leave it where it is. A vehicle pulled over soon very seldom has permanent damage, since the fuel drain and the flush, which still go first, deal with it.
Myths The Holmes drivers hear about petrol in a diesel
False: topping up to full with diesel makes it fine. It does not. Topping up removes nothing; it gives you a bigger tank of the same mix. The idea behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the reverse. At higher pressure, through more precise components: that's how a newer diesel moves its fuel, so the lubrication matters more, not less.
One myth that catches people out: if it starts and drives, it must be unharmed. The motorist of a petrol engine fed diesel usually has no choice but to stop, since it will not run, and the damage stops there. Whilst the pump grinds, a diesel fed petrol usually starts, idles and drives away as though nothing has happened. Fine and running aren't the same thing.
Myth: "Add some two-stroke oil and drive the car home." It is an old fix for a different issue. None of what petrol diluted gets put back by it — and afterwards, that tank still holds that petrol.
Once the engine has been run, part of the petrol sits in the filter and your lines, not that tank — and the next start sends it right back through the pump. So the myth "drain your tank yourself and you are sorted" does not stand up. Also, a can of petrol drained by the roadside is truly risky.
Why petrol in a diesel happens so easily
It's rarely carelessness, and nobody does it on purpose. 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 simple, and the mistake runs one way.
When habit and the car stop matching, it occurs. A motor that's new to you — hired, on loan as a courtesy car, or brand new. Two motors on one drive, one petrol, one diesel. Your ordinary forecourt, its pumps suddenly in a different order. Fuelling up in a rush on the way to Derby, with a train to catch. The first fill-up in a diesel Renault Megane after years of driving petrol is exactly the moment it happens. Throw in rain, a phone call or a back seat full of kids, and the hand repeats what it has always done.
Preventing petrol in a diesel next time you fill up in The Holmes
- Read the petrol pump, not the colour. In the UK unleaded handles are usually green and diesel black, but not on each forecourt. The label is what counts.
- Many motors state the fuel inside the filler flap or on the cap, and so check it on the first fill in a car you do not know.
- A coloured fob or a sticker on the diesel's key does more than any amount of intending to remember, for a home with one of each.
- Before the nozzle leaves the petrol pump the first time you fill a hired or new motor, say "diesel" aloud. Daft, perhaps, but it works.
- Put the phone away. This is an easy mistake to make while you're thinking about something else.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler designed to refuse a petrol nozzle, and add-on devices exist for vehicles without one. They are a safety net, not a reason to stop reading the petrol pump.
- Stop the moment you notice. Less petrol inside that tank means a weaker blend. It doesn't change what to do next, which is still not to crank it.
Put petrol in a diesel in The Holmes already?
Short and simple, then, is the order of things. Starting it is out, and so is turning on your ignition. If you are still on the forecourt — Texaco or anywhere else — ask the attendants to help you push the car away from the pump. Phone 0333 366 0103 next, with three facts — your fuel, the approximate amount, and whether it has run.
Corrosion and deposits are the problem with AdBlue, whereas petrol means lost protection. So if it was AdBlue, say so — and see its own The Holmes page.
The Holmes petrol in a diesel tasks: why one costs more than another
A fair single price does not exist here: four scenarios, four separate jobs. Which of them you're in is chiefly what moves the cost. Where the car is matters too, and whether a technician can safely reach it, after the share of petrol to what that tank takes.
What got in, how much, and whether it's run — three queries we ask before quoting, not after, for exactly that reason. The answers change a range into a straight figure.
About The Holmes
The Holmes is a suburban area located on the riverside in Derbyshire, with a mix of flat dwellings and other residential properties. The Holmes sits near the city of Derby, at an elevation of around 52 metres, and is close to nearby places such as Litchurch and Little Chester. The Holmes is part of the larger Derby urban area, with the city centre just 0.4 miles away. The Holmes has a population of approximately 3484 residents.
Across Derbyshire and in The Holmes: fuel drain cover
Petrol in diesel call-outs in The Holmes — part of the DE postcode area — go to vans that also cover the locations around it, Derby, Litchurch and Little Chester among them. A forecourt, a supermarket car park, a lay-by or your own drive are all locations our technicians drain, and your car does not need to move to us.
In The Holmes and still at the pump?
In that case, you could not be in a better spot. Ring, and keep it turned off.