Tentergate: Petrol in a Diesel Car? How Worried to Be
Provided it hasn't been started, worry far less than you probably are. "Have I wrecked it?" is the first question everyone in Tentergate asks, and the truthful answer is usually no, since petrol left in a diesel tank hurts nothing until it is drawn through the fuel system — by ignition priming, by the starter, or by driving. To leave it that way, phone Petrol in Diesel then leave your engine switched off. The rest of this page sets out what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you again.
What petrol in a diesel does to your engine
On its way through an engine, diesel does two tasks. Before it combusts, it lubricates — then it ignites. Designed to very fine tolerances, the injectors and the pump depend on your diesel moving through them to stop their surfaces wearing against one another.
Poorly at the first, not at all at the second: that's petrol. It's runnier than diesel and removes the lubrication the system hinges 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 opposite of what a diesel needs from its fuel. That's where the knocking comes from.
The shape of the issue is clear once you put those together. It's movement that causes the damage, not contact. Petrol in the tank is a fuel issue. A pump that has been working on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with your fuel to your injectors downstream.
Tentergate, petrol in a diesel: four situations, from mild to significant
Fuelled but not once started — as good as it gets. Being at a forecourt is what makes this the case: elsewhere, your car has been driven there to begin with. With that petrol kept in that tank alone, it's drained and purged right where it stands, and nothing more is needed.
Ignition on, or started for a second. Once primed, your system has pulled petrol out of your tank up to your filter and the lines. Normally little more than draining, rinsing and seeing to your filter, and so still straightforward.
Those few miles on the road were the pump running on fuel weakened by petrol throughout. How hard the car was driven matters as much as how far, and the work covers your tank, your lines, your filter and fresh fuel through the whole system. Short trips, like the school run to St Mary's Primary School Knaresborough, A Voluntary Catholic Academy, are one thing. Very different again: a run to Ripon, under 10 miles away, or some miles on the A1(M), under 5 miles from Tentergate, where the engine kept working hard.
Rattling, a lumpy idle, smoke, a throttle gone soft: driven till it complained. The motor is telling you the fuel is no longer acting like diesel. Stop wherever you are — the verge on Coverdale Drive, a lay-by, a side street — then leave the car there. What goes first is still the fuel drain and flush-through, and that deals with it, with permanent damage very uncommon if a vehicle is pulled over quickly.
What Tentergate drivers get told about petrol in a diesel — and the myths in it
It will not be fine. The myth: "Fill it the rest of the way with diesel and it will be." Nothing comes out when you top up — that tank just carries more of the same mixture. That advice supposes a diesel fuel system tolerates petrol by percentage. It does not.
"Current diesels can handle a little petrol" — a myth, and closer to the reverse. Smaller parts and higher pressure are the way a current diesel runs its fuel, and that makes the lubrication matter more, not less.
Myth: "If it starts and drives, there's no damage done." This is the one that fools people. Any petrol engine fed diesel normally will not run, and so the motorist stops and the damage stops with them. Feed petrol to a diesel and it normally starts, ticks over and drives away as if nothing happened — all the while its pump is wearing. Running isn't the same as fine.
Myth: "Add some two-stroke oil and drive it home." It's an old fix for a separate fault. It doesn't put back what petrol has thinned, and that petrol is still in the tank after that.
Myth: "Drain the tank yourself and you are sorted." Once the engine has run, some of that petrol is no longer inside the tank: it's in the filter and the lines, and it goes straight back through your pump on your next start. Draining petrol into a can by the roadside is also really risky.
Why petrol in a diesel occurs so easily
On purpose? Never. Through carelessness? Seldom, if ever. The petrol nozzle is the smaller of the two and slips into a diesel filler with almost no resistance; a diesel nozzle generally will not go into a petrol vehicle at all. The forecourt makes it simple, and the error runs one way.
The moment routine stops matching the car is the moment it occurs. Courtesy car, hire car, or a motor that's brand new. Two motors on one driveway, one petrol, one diesel. A forecourt you know, only with its pumps arranged differently. A train to catch, and a hurried fill en route to Knaresborough. A new-to-you diesel Volkswagen Tiguan, its first fuelling, and a driver used to petrol: precisely when it occurs. Throw in rain, a phone call or a back seat full of children, and the hand does what it has always done.
Preventing petrol in a diesel next time you fill up around Tentergate
- Not every forecourt in the UK follows green for unleaded and black for diesel, even if most generally do. Read the pump's label; the colour is only a clue.
- The first fill in a strange car is the time to check your filler flap — inside it, or on the cap, many cars state which fuel they take.
- A coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember, for a household with one of each.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump. It sounds silly and it works.
- Thinking about something else is when this becomes an easy mistake to make, and so tuck your phone away and keep your mind on the pump.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler built to block a petrol nozzle, and add-on devices are available for cars without one. They are a backstop, not a reason to stop reading the petrol pump.
- Noticing it halfway? Stop there and then. A weaker blend follows from less petrol inside the tank, yet the next stage remains the same: don't crank it.
Put petrol in a diesel around Tentergate already?
Short and simple, then, is the order of things. Leave it unstarted, with your ignition off too. The staff on the forecourt — whether at Asda itself or wherever you filled up — will usually help roll it clear of the petrol pump if you ask. Call 0333 366 0103 next, with three facts — the fuel, the rough volume, and whether it's run.
AdBlue, not petrol? Then say so. Corrosion and deposits, not lost protection, make it a separate issue — Tentergate has a page all for it.
One petrol in a diesel task around Tentergate costs more than another. Why?
There is no honest single quote for this, because the four scenarios above are four different jobs. What moves the cost is mostly which of them you are in. Two things come after that: the petrol that went in as a share of what the tank holds, then the spot the vehicle is in and whether a technician can get to it safely.
Three queries come first, before quoting, instead of after — what went in, how much, has it run — and that is the reason. A range turns into a straight figure once the answers are in.
About Tentergate
Tentergate is a suburban area situated on the riverside in North Yorkshire, with an elevation of 74 metres and a population of approximately 2666 residents. Tentergate is located near the cities of Ripon and Knaresborough, and is close to the smaller communities of New Scriven and Scriven. Tentergate is characterized by its predominant semi-detached housing stock, reflecting the typical residential architecture of the region. Tentergate sits within a wider landscape of rolling hills and valleys, about 182 miles north of London.
Tentergate and North Yorkshire: where our fuel drain cover reaches
New Scriven, Scriven and Knaresborough are among the spots near Tentergate that the same teams work, answering petrol in diesel call-outs across Tentergate's HG postcode area. Our engineers drain where your car is — your own driveway, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
In Tentergate and still at the pump?
In that case, you couldn't be in a better spot. Turned off it stays; then phone.