Howden: Petrol in a Diesel Car? How Worried to Be
Not started? Then less worried than you probably are. Petrol resting in a diesel tank does nothing to your motor till something pulls it through your fuel system — your ignition priming the pump, your starter, or driving on its own. So the fair answer to the first query everyone around Howden asks, "have I wrecked it?", is usually no. Keep it that way: leave the motor off then call Petrol in Diesel. Read on for three things: the effect petrol has inside a diesel motor, the signs of how far it has spread, and ways to make sure you never repeat it.
Petrol in a diesel: what does it do to your engine?
Two jobs fall to diesel on its journey through a motor. Lubricating comes before burning; it does both. Your high-pressure pump and the fuel injectors are designed to very fine clearances, and your diesel passing through them is what keeps those surfaces from grinding against one another.
Poorly at the first, not at all at the second: that is petrol. It is thinner than diesel and takes away the lubrication the fuel system depends on, so a pump running on a petrol mixture 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 clattering comes from.
Taken together, they make clear what shape the trouble takes. Contact doesn't do the harm — movement does. Where the petrol is only inside the tank, it is an issue of fuel, nothing more. Once the pump has been labouring on that petrol, a mechanical problem has begun: whatever is shed by a pump that is wearing down is carried downstream to your injectors with the fuel.
Howden, petrol in a diesel: four situations, from mild to serious
Fuelled but never started — the best it gets. Just that tank has petrol in it, so the task is clearing your tank and cleaning your system where your car stands. This situation can only really happen at a forecourt: anywhere else, the vehicle got there by being driven.
A brief spell of running, or merely your ignition on. With your system primed, the fuel lines and filter now contain petrol that has come from your tank. Drain, flush, deal with the fuel filter: still usually simple.
Some miles driven, and the pump has spent every one of them labouring on weakened fuel. How hard your car was driven counts as much as how far, and the work covers your tank, your lines, the filter and fresh fuel through the whole circuit. A school run to Howden Junior School is one matter. Any mileage on the M62, under a mile from Howden, means the motor has worked hard throughout, and a run to York, under 25 miles away, makes a very different job as well.
It complained, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone uneven. What you are hearing is your motor reporting fuel that no longer runs like diesel. Pull up wherever you are — the verge on Northolmby Street, a lay-by, a side street — then leave the car there. The drain and flush still come first, and they deal with it: if a vehicle is stopped early, lasting damage is very uncommon.
Howden people and the petrol in a diesel stories they hear
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Nothing is removed when you top up — that tank simply carries more of the same blend. That advice presumes a diesel fuel system handles petrol by percentage. It does not.
Myth: "A current diesel can cope with a bit of petrol." If anything, the reverse. Smaller parts and higher pressure are how a current diesel runs its fuel, and that makes the lubrication count more, not less.
"It starts, it drives, and so no harm done" — the myth that catches most drivers than any other. Diesel in a petrol motor usually means a motor that won't run: the motorist stops, and so does the harm. Feed petrol to a diesel and it usually starts, ticks over and drives away as if nothing happened — all while its pump is wearing. Being able to run isn't proof of being fine.
Myth: a two-stroke additive makes it safe to drive home. It is an old fix, supposed for another fault. The petrol is still inside the tank after that, and whatever it has thinned is not put back.
If the motor has run, part of that petrol sits in the filter and the lines, not the tank — and your next start pulls it right back through your pump. So the myth "drain your tank yourself and you are sorted" doesn't stand up. Emptying petrol into a can at the kerbside is also genuinely risky.
How it happens: petrol in a diesel
On purpose? Never. Through carelessness? Rarely, if ever. A diesel nozzle mostly will not go into a petrol motor, yet the slimmer petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one mistake simple, and only in that direction.
When habit and the car stop matching, it occurs. Courtesy car, hire car, or a motor that is new. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a well-known forecourt. A rushed fill en route to the nearest station with a train to catch. Precisely the moment it happens: after years of driving petrol, a driver fills a diesel Volkswagen Passat for the first time. The hand does what it has always done once you add rain, a phone call or a back seat full of kids.
Howden motorists: how to prevent petrol in a diesel next time
- The label is what matters, so check the pump rather than the colour: in the UK unleaded handles are normally green and diesel black, yet not on every forecourt.
- Check the filler flap. Many vehicles state the fuel type inside the flap or on the cap. Look at it on the first fill in a vehicle you don't know.
- Good intentions do less than a sticker or a fob in a vivid colour on the diesel's key when a house has one of each. So label it.
- "Diesel", aloud, before you lift the nozzle — every time a new or hired car gets its first tank. It sounds silly. It works.
- Thinking about something else is when this becomes an easy mistake to make, so tuck the phone away and keep your mind on the pump.
- Some diesels come with a filler built to reject a petrol nozzle, and devices you can add are available for cars 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 makes a weaker mix, so stop the moment you realise — though remembering that the next step is unchanged. It is still not to crank it.
Howden: already put petrol in a diesel?
The order of things is brief, then. Leave it unstarted, with the ignition switched off as well. If you are still on the forecourt — BP or anywhere else — ask the attendants to help you roll the car clear of the petrol pump. Then ring 0333 366 0103 and tell us what went in, about how much, and if it has run.
If it was AdBlue and not petrol, say so. That's a different issue — corrosion and deposits and not lost lubrication — and it has its own page for Howden.
Howden petrol in a diesel jobs: why one costs more than another
Four separate jobs sit behind the four situations above — which is why there is no honest single price. What shifts the cost is chiefly which of them you're in. After that it's the share — how much petrol got in against how much that tank takes — and then where the vehicle is and whether a technician can reach it safely.
Three questions come first, before quoting, instead of after — what got in, how much, has it run — and this is the reason. Those replies change a range into a straight figure.
About Howden and its setting
Howden is a town in the East Riding of Yorkshire, situated inland near the River Ouse and close to the M62 motorway. Howden sits at a low elevation of around 8 metres, with the town's detached housing stock reflecting its relatively affluent character. Howden is located near several smaller settlements, including Knedlington and Howdendyke, and is within commuting distance of the city of York. Howden has a population of approximately 4572 people.
Howden and East Riding of Yorkshire: where our fuel drain cover runs
Petrol in diesel call-outs in Howden — part of the DN postcode area — go to teams that likewise cover the spots round it, Knedlington, Howdendyke and Kilpin Pike among them. Our technicians 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.
In Howden and still at the pump?
Then you are in the best place there is. Keep it turned off, and ring.