Knockhall: Petrol in a Diesel Car? How Worried to Be
Unstarted? Then less worried than you probably are. Till your ignition primes the pump, the starter cranks, or your vehicle is driven, petrol in a diesel tank just sits there and does no harm. Which makes the truthful reply to that first Knockhall query — "have I ruined it?" — usually no. Keep it like that: leave the engine off then ring Petrol in Diesel. The rest of this page covers what petrol really does to a diesel, how to tell how far it has got, and how to make sure it does not happen to you a second time.
Petrol in a diesel: what does it do to the motor?
Two tasks fall to diesel on its route through a motor. Lubricating comes before burning; it does both. Extremely fine gaps are built into your injectors and the high-pressure pump, and only your diesel flowing through stops their surfaces grinding together.
Petrol does the first job poorly and the second not at all. The knocking comes from petrol being made 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.
Seen together, they show what shape the issue takes. The damage is done by movement, not by contact. Any tank with petrol in it is a fuel fault. The start of a mechanical problem is a pump that has been labouring on that petrol — and whatever a worn pump sheds travels on with the fuel to your injectors downstream.
Four situations we see around Knockhall: how serious is petrol in a diesel?
The best case there can be: filled up, never started. That petrol is in that tank and just the tank, and the task is a drain and a flush where the car stands. This is the one situation that can only really take place on a forecourt, as anywhere else the vehicle has been driven to get there.
The ignition switched on, or a short start. Petrol has left your tank and got to the fuel filter and the fuel lines, since the fuel system has been primed. Normally little more than draining, rinsing and seeing to your filter, so still straightforward.
Driven a couple of miles. Now your pump has spent those miles working on weakened fuel. How hard the vehicle was driven counts as much as how far, and the work covers your tank, your lines, your filter and clean fuel through the whole circuit. On the school run to Knockhall Primary School, the mileage is short. A run as far as London, under 25 miles away, is a very different job. So is any miles on the M25, under 3 miles from Knockhall, where the motor has been labouring hard the whole time.
Knocking, a lumpy idle, smoke, a throttle gone soft: driven till it complained. The motor is telling you your fuel is no longer behaving like diesel. Stop on the spot — on the verge on Eynsford Road, at the kerb, down a side road — and do not move it. Lasting damage is very unusual if a vehicle is stopped soon, and the drain and flush that still come first sort it out.
Petrol in a diesel myths Knockhall people hear
It will not be fine. The myth: "Fill it the rest of the way with diesel and it'll be." Nothing is removed by topping up — you're left with a fuller tank, still the same mix. That advice assumes a diesel fuel system handles petrol by percentage. It does not.
Not so: a modern diesel copes with a bit of petrol. If anything, the opposite. Lubrication counts more on modern diesels, not less, since their fuel passes through finer components at higher pressure.
One myth that catches motorists out: if it starts and drives, it must be unharmed. A petrol engine fed diesel normally will not run, and so the driver stops and the harm stops with them. Whilst the pump wears, a diesel fed petrol usually starts, ticks over and drives away as though nothing has happened. A running engine doesn't mean fine.
An old fix for a different fault lies behind this one. Myth: "Add some two-stroke oil and drive it home." What petrol has diluted stays diluted, and the petrol remains inside that tank regardless.
Myth: "Drain the tank yourself and you're sorted." After your engine has been run, some of the 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. It's also truly dangerous to drain petrol into a can at the kerbside.
Petrol in a diesel: how does it take place?
On purpose? Never. Through carelessness? Seldom, if ever. A diesel nozzle generally won't fit a petrol motor, but the narrower petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one error easy, and just in that direction.
The moment habit stops matching your car is the moment it occurs. Courtesy car, hire car, or a vehicle that is new. Two vehicles on one driveway, one petrol, one diesel. A forecourt you know, but with its pumps arranged differently. Filling up in a rush on the way to Greenhithe for Bluewater, with a train to catch. Years of petrol cars behind you, a diesel Volkswagen Tiguan in front of you at the forecourt for its first tank — that is when. The hand does what it has always done when you add rain, a phone call or a back seat full of children.
Next time you fill up in Knockhall: preventing petrol in a diesel
- Read the pump, not the colour. In the UK unleaded handles are normally green and diesel black, yet not on every forecourt. The label is what matters.
- Many motors state the fuel inside your filler flap or on the cap, so check it on the first fill in a 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 home has one of each. So mark it.
- It seems silly and it does the trick: on your first fill in a new or hired car, say "diesel" aloud before you lift the nozzle off the pump.
- Put your phone away. This is an easy mistake to make whilst you are thinking about something else.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler designed to refuse a petrol nozzle, and aftermarket devices exist for the rest. Count it as a backstop, then keep reading the petrol pump.
- The moment you realise, stop: less petrol in that tank means a thinner mix. What to do next doesn't change, though — still do not fire it up.
Put petrol in a diesel around Knockhall already?
Short and simple, then, is the order of things. Do not switch the ignition on, and do not start it. Ask the attendants to help you push it clear of the petrol pump if you are still at the forecourt, whether that's Esso or somewhere else. Call 0333 366 0103 next, with three facts — your fuel, the rough amount, and if it has run.
Corrosion and deposits form the issue with AdBlue, whereas petrol means lost lubrication. So if it was AdBlue, say so — and read its own Knockhall page.
Why one petrol in a diesel job around Knockhall costs more than another
An honest single price doesn't exist here: four situations, four separate tasks. The scenario itself does most of the work of moving the cost. Where your car is matters too, and whether a technician can safely reach it, after the ratio of petrol to what your tank holds.
Before any quote, not after, come three queries: your fuel that was put in, the volume, and if it's run. That's why. A range turns into a straight figure when those answers are in.
About Knockhall, briefly
Knockhall is a suburban area in Kent, situated inland at an elevation of 36 metres, approximately 17 miles from London. Knockhall is characterized by its predominantly terraced housing and is located near the towns of Greenhithe and Swanscombe. Knockhall is also close to the major shopping centre at Bluewater, which attracts visitors from the surrounding area. Knockhall has a population of around 4998 residents.
Fuel drain cover across Kent, Knockhall included
Knockhall waits in the DA postcode area, and the vans that answer petrol in diesel calls there work the locations near it as well — Greenhithe, Swanscombe and Bluewater among them. You need not bring your car to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all spots where we work.
At the pump around Knockhall, right now?
The best spot there is, then — that is where you are. Turned off it stays; then phone.