Low Moorsley: Petrol in a Diesel Car? How Worried to Be
Far less than you likely are, provided it hasn't been started. Until your ignition primes your pump, your starter cranks, or the car is driven, petrol in a diesel tank just sits there and does nothing. Which means the truthful reply to that first Low Moorsley query — "have I wrecked it?" — normally no. Leave the engine off and call Petrol in Diesel — that keeps it like that. Keep reading for three things: the effect petrol has inside a diesel engine, the signs of how far it has spread, and ways to make sure you never do it again.
Inside your engine: what petrol in a diesel does
Diesel does two tasks on its way through an engine. It lubricates first, and after that does it burn. What stops the surfaces inside your high-pressure pump and the fuel injectors from wearing against each other is your diesel flowing through them — they're designed to extremely fine gaps.
Of these two jobs, petrol handles the first badly and the second not at all. A pump working on a petrol mixture is wearing itself out, because petrol is runnier than diesel and strips out the protection your fuel system relies on. Petrol is also designed to resist igniting under compression — the opposite of what a diesel needs from its fuel — and that's where the knocking starts.
The shape of the problem is clear when you put those together. Not contact but movement is what does the damage. Where that petrol is only in your tank, it's an issue of fuel, nothing more. Whatever a worn pump sheds goes on, carried by your fuel, into your injectors further along, which is why a pump that has been working on the petrol is where a mechanical problem starts.
How bad is petrol in a diesel? Four scenarios our technicians see in Low Moorsley
The best case there can be: filled up, not once started. On a forecourt, and truly only there, the petrol is still limited to your tank — since everywhere else your car was driven to get to it. The job is emptying and rinsing on the spot.
A brief spell of running, or merely your ignition on. Petrol has come out of your tank and got to the filter and the fuel lines, since the system has been bled. Normally nothing more than emptying, rinsing and sorting the fuel filter, so still straightforward.
Your pump has worked a couple of miles on weakened fuel — that's what driving the vehicle meant. How hard your car was driven counts as much as how far, and the work takes in your tank, the fuel lines, your filter and fresh fuel through the whole circuit. On the school run to Hetton Primary School, the mileage is small. Getting as far as Durham, under 10 miles away, makes a very different task — as does any mileage on the A1(M), under 3 miles from Low Moorsley, with the motor working hard all the way.
It complained, and only then stopped: smoke, knocking, a throttle gone soft, an idle gone lumpy. That is your motor telling you its fuel has stopped acting like diesel. Whether it's the verge on Weardale Street, a lay-by or a side street, stop where you are and leave it. The fuel drain and flush still go first, and they take care of it: when a vehicle is stopped soon, permanent damage is very rare.
What Low Moorsley motorists get told about petrol in a diesel — and the myths in it
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. A bigger tank of the same mixture is all you get, because topping up takes out nothing. A diesel fuel system doesn't accept petrol by percentage in the way that advice assumes.
If anything, the reverse is true. Myth: "A newer diesel can cope with a bit of petrol." Lubrication counts more on newer diesels, not less, because their fuel runs through more precise components at higher pressure.
This is the one that catches people. Myth: "If it starts and drives, there is no damage done." Feed diesel to a petrol engine and it usually will not run, and so the motorist stops — and the harm stops with them. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile your pump wears. Being able to run is not proof of being fine.
Myth: a two-stroke additive lets you to drive home. It was an old workaround, meant for another fault. It doesn't put back what petrol has thinned, and that petrol is still in that tank later.
Once the engine has run, part of that petrol is in your filter and the fuel lines, not that tank — and the next start sends it right back through your pump. So the myth "drain the tank yourself and you are sorted" doesn't stand up. Besides, petrol emptied into a can by the road is genuinely dangerous.
How it happens: petrol in a diesel
No one does it on purpose, and it is rarely carelessness. 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 car at all. So the slip runs one way.
Habit and the car getting out of step is how it occurs. A new vehicle, a hire car or a courtesy car. One petrol and one diesel on the driveway of the same household. A forecourt you know, only with its pumps arranged differently. Racing for a train at Durham and fuelling up en route. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist accustomed to petrol: exactly when it takes place. Throw in a back seat full of kids, a phone call or rain, and the hand takes over.
Next time you fill up in Low Moorsley: 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 vehicle is the time to check the filler flap — inside it, or on the cap, many cars state which fuel to use.
- Good intentions do less than a sticker or a fob in a vivid colour on your diesel's key if a household has one of each. So mark it.
- Say it before you lift it. On the first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the petrol pump. It sounds daft and it works.
- Mistakes like this are straightforward to make whilst your mind is on something else, and so the phone goes away.
- Some diesels come with a filler designed to refuse a petrol nozzle, and devices you can add exist for motors without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop reading the petrol pump.
- Less petrol means a weaker mixture, so stop as soon as you realise — though remembering that the next step is unchanged. It's still not to start the vehicle.
Put petrol in a diesel around Low Moorsley already?
The order of things is short, then. Never crank it, and don't switch your ignition on. If you're still on the forecourt — Gulf or anywhere else — ask the staff to help you roll the car clear of the pump. Ring 0333 366 0103 next, with three facts — your fuel, the rough quantity, and if it has run.
Corrosion and deposits form the issue with AdBlue, whereas petrol brings lost protection. So if it was AdBlue, say so — and see its own Low Moorsley page.
Why one petrol in a diesel task in Low Moorsley costs more than another
The four situations above are four separate jobs, so no single price for this would be honest. What shifts the cost is chiefly which of them you are in. After that it's the proportion — how much petrol got in against how much that tank takes — and then where your car is and whether our van can reach it safely.
That is why we ask three questions before costing rather than after: what was put in, how much, and whether it has run. The answers turn a range into a straight figure.
About Low Moorsley, for a moment
Low Moorsley is a suburban area in Tyne and Wear, situated inland at an elevation of 97 metres, approximately 5 miles from Durham. Low Moorsley is characterised by its semi-detached housing stock and forms part of the wider residential area surrounding Durham. Low Moorsley is close to nearby places such as High Moorsley, Middle Rainton, and Hetton-le-Hole, and is about 235 miles north of London.
Across Tyne and Wear and around Low Moorsley: fuel drain cover
Low Moorsley waits in the DH postcode area, and our teams that answer petrol in diesel call-outs there work the locations near it as well — High Moorsley, Middle Rainton and Hetton-le-Hole among them. No need to move the vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all spots where we work.
At the pump in Low Moorsley, right now?
The best spot there is, then — that is where you are. Keep it off. Ring.