Oldmeldrum: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less worried than you probably are. Till your ignition primes your pump, your starter cranks, or the vehicle is driven, petrol in a diesel tank simply sits there and does no harm. Which means the honest reply to that first Oldmeldrum query — "have I ruined it?" — normally no. Keep it that way: leave the motor off and call Petrol in Diesel. Further down, you will find what petrol actually does inside a diesel, how far it may have got, and how to stop it happening to you again.
The motor and petrol in a diesel: what goes on
Two jobs fall to diesel on its route through a motor. Before it combusts, it lubricates — then it combusts. Made to extremely fine gaps, the fuel injectors and the pump rely on your diesel moving through them to stop their surfaces wearing against one another.
The second task petrol does not do at all, and the first it does poorly. It's thinner than diesel and strips away the protection the system hinges on, so a pump running on a petrol blend 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's where the rattling comes from.
Seen together, they show the shape the issue takes. Not contact but movement is what causes the damage. All a tank with petrol in it amounts to is a fuel problem. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with the fuel to your injectors further on.
Four scenarios we see in Oldmeldrum: how bad is petrol in a diesel?
Fuelled, and never started: nothing beats it. That petrol is inside that tank and just your tank, and the job is a drain and a flush where the car sits. This is the one scenario that can only really occur on a forecourt, as anywhere else the car has been driven to get there.
Ignition on, or started for a moment. With the system primed, the lines and filter already hold petrol that has come from that tank. Normally little more than draining, cleaning and sorting your filter, and so still easy.
The pump has spent a couple of miles on thinned fuel — that is what driving it meant. Miles is only half of it; how hard it was driven counts just as much. Either way this work includes the tank, your lines, the fuel filter and fresh fuel through the whole system. Short trips, like the school run to the local primary school, are one thing. Getting as far as Aberdeen, under 25 miles away, makes a very different job — as does any distance on the M90, over 50 miles from Oldmeldrum, with the engine working hard all the way.
Clattering, a ragged idle, smoke, a throttle gone soft: driven till it complained. What you are hearing is your engine signalling fuel that no longer acts like diesel. Stop on the spot — on the verge on Commercial Road, at the kerb, down a side road — and don't move it again. A vehicle stopped quickly very rarely has lasting damage, since the drain and the flush, which still go first, take care of it.
Stories Oldmeldrum motorists hear about petrol in a diesel
False: topping up to full with diesel makes it fine. It doesn't. Topping up removes nothing; it gives you a bigger tank of the same mixture. The idea behind the advice — that diesel fuel systems accept petrol by percentage — is wrong.
"Newer diesels can handle a little petrol" — a myth, and closer to the opposite. A modern diesel runs its fuel through more precise components at higher pressure, which makes the protection count more, not less.
"It starts, it drives, so no harm done" — the myth that catches more people than any other. A petrol engine fed diesel generally will not run, so the driver stops and the damage stops with them. A diesel fed petrol generally starts, idles and drives away as if nothing has happened, while your pump grinds. Running isn't the same as fine.
Not so: a two-stroke additive lets you to drive home. It is an old workaround, supposed for another problem. None of what petrol thinned gets put back by it — and afterwards, your tank still contains that petrol.
"Drain it yourself and you're sorted" — a myth, since after it's been running some petrol sits in the filter and lines, ready to go straight back through your pump on the next start. Also, a can of petrol filled at the roadside is genuinely hazardous.
How petrol ends up: petrol in a diesel
It is rarely carelessness, and no one does it on purpose. The forecourt makes it easy: the petrol nozzle is the narrower of the two, and it slips into a diesel filler with almost no resistance, while a diesel nozzle mostly won't go into a petrol motor at all. So the mistake runs one way.
Routine and your car getting out of step is how it occurs. Any motor that is new to you — a hire car, on loan as a courtesy car, or just bought. One petrol and one diesel on the drive of the same household. A well-known forecourt with the pumps in a different order. Rushing for a train at Inverurie and filling up en route. Precisely the moment it takes place: after years of driving petrol, someone fills a diesel Skoda Octavia for the first time. Your hand does what it has always done when you add rain, a phone call or a back seat full of children.
Oldmeldrum motorists: how to avoid petrol in a diesel next time
- Check the 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.
- Inspect your filler flap. Many cars state the fuel inside the flap or on the cap. Look at it on the first fill in any vehicle you don't know.
- Good intentions do less than a sticker or a fob in a bright 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" out loud before you lift the nozzle off the petrol pump. It sounds silly and it works.
- While you're thinking about something else, this is an easy mistake to make — so put your phone away.
- Add-on devices exist for vehicles without one, and some diesels are built with a filler that won't take a petrol nozzle. Useful — but a backstop only, never a reason to stop checking the label.
- Stop as soon as you realise. Less petrol inside the tank means a thinner mix. It doesn't change what to do next, which is still not to crank it.
Oldmeldrum: already put petrol in a diesel?
The order of things is short, then. Don't switch the ignition on, and don't fire it up. The attendants at the forecourt — whether at Meldrum Motors itself or wherever you filled up — will normally help push it away from the pump if you ask. Then call 0333 366 0103 and tell us what got in, about how much, and whether it has run.
Say so if it was AdBlue rather than petrol: it's a separate problem, with its own page for Oldmeldrum, since AdBlue brings corrosion and deposits rather than lost protection.
One petrol in a diesel task in Oldmeldrum costs more than another. Why?
A fair single quote doesn't exist here: four scenarios, four separate tasks. Mostly, the cost moves with which one you're in. Where your car is matters too, and whether our van can safely get to it, after the ratio of petrol to what the tank takes.
What was put in, how much, and whether it has run — three questions our technicians ask before costing, not after, for exactly that reason. Those answers turn a range into a straight figure.
About Oldmeldrum
Oldmeldrum is a town situated on the River Don in Aberdeenshire, with a mix of older and modern housing, predominantly detached homes. Oldmeldrum sits at an elevation of 116 metres, near the villages of Whitefield and Mosshead, and is located approximately 15 miles from Aberdeen. Oldmeldrum has a population of around 3178 residents, who enjoy the town's riverside setting and surrounding countryside. Oldmeldrum is also close to the Kirkton of Bourtie, a nearby settlement with its own distinct character.
Oldmeldrum and Aberdeenshire: where our fuel drain cover reaches
Oldmeldrum waits in the AB postcode area, and our teams that answer petrol in diesel call-outs there work the locations near it as well — Whitefield, Mosshead and Kirkton of Bourtie among them. Our engineers drain wherever the vehicle is — your own drive, a lay-by, a supermarket car park, a forecourt — so it never needs to come to us.
At the pump in Oldmeldrum, still?
In that case, you couldn't be in a better spot. Turned off it remains; then phone.