Tadworth: Petrol in a Diesel Car? How Worried to Be
Far less than you likely are, if it hasn't been started. Till your ignition primes your pump, the starter turns, or the vehicle is driven, petrol in a diesel tank simply waits there and does no harm. Which makes the honest reply to that first Tadworth query — "have I wrecked it?" — normally no. Keep it that way: leave your engine off then phone Petrol in Diesel. What petrol actually does to a diesel, how to judge how far it has travelled, and how to keep it from happening again: that is the remainder of this page.
What petrol in a diesel does to your engine
Diesel has two tasks on its way through a motor. Lubricating comes before burning; it does both. What keeps the surfaces inside your high-pressure pump and the fuel injectors from wearing against each other is your diesel flowing through them — they are designed to extremely fine clearances.
Petrol does the first task badly and the second not at all. Being less viscous than diesel, petrol strips away the protection a fuel system needs, leaving a pump on the mixture to wear itself. It's equally made to resist igniting under compression — the opposite of what a diesel needs — which is where you hear the clattering.
Together, those make the shape of the trouble clear. Not contact but movement is what causes the harm. A tank with petrol in it is a fuel problem. The beginning of a mechanical one is a pump that has been labouring on that petrol — and whatever a worn pump sheds moves on with your fuel to the injectors beyond it.
Tadworth, petrol in a diesel: four cases, from mild to significant
The best case there is: filled up, not once started. That petrol is in the tank and only your tank, and the job is a drain and a flush where your car sits. This is the one scenario that can only truly take place at a forecourt, because anywhere else your car has been driven to get there.
Your ignition switched on, or a brief start. Once primed, the fuel system has pulled petrol out of your tank as far as the filter and the fuel lines. Usually little more than draining, rinsing and sorting the fuel filter, and so still simple.
The pump now worked a couple of miles on weakened fuel — that's what driving the car does. How hard the car was driven counts as much as how far, and the work covers your tank, the fuel lines, your filter and clean fuel through the whole system. The school run to Tadworth Primary School is one matter. Getting as far as Westminster, under 25 miles away, makes a very different job — as does any mileage on the M25, under 3 miles from Tadworth, with the engine labouring hard the whole time.
Rattling, a ragged idle, smoke, a throttle gone soft: driven until it complained. What you are hearing is the engine signalling fuel that no longer behaves like diesel. Stop wherever you are — the verge on Cross Road, a lay-by, a side street — and leave the car where it is. The fuel drain and flush still come first, and they deal with it: when a car is stopped soon, long-term damage is very rare.
Tadworth motorists and that petrol in a diesel stories they hear
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It will not. Nothing is removed by topping up — you are left with a fuller tank, still the same mixture. A diesel fuel system doesn't accept petrol by percentage in the way that guidance assumes.
"Newer diesels can handle a little petrol" — a myth, and nearer the opposite. Lubrication counts more on modern diesels, not less, since their fuel passes through finer parts at higher pressure.
"It starts, it drives, so there is no harm" — the myth that catches more motorists than any other. The driver of a petrol engine fed diesel normally has no choice but to stop, because it will not run, and the harm stops there. Nothing seems to have happened when a diesel fed petrol fires up, ticks over and drives away, as it usually does; meanwhile the pump wears. Fine and running are not the same thing.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a separate fault. The petrol is still in the tank after that, and whatever it has diluted isn't put back.
"Drain it yourself and you are sorted" — a myth, because after it has been running some petrol lies in the fuel filter and lines, ready to go straight back through the pump at the next start. It is also genuinely hazardous to drain petrol into a can by the kerbside.
How it happens: petrol in a diesel
Carelessness is seldom the cause, and no one means to do it. The petrol nozzle is the slimmer of the two and slides into a diesel filler with almost no resistance; a diesel nozzle generally won't go into a petrol motor at all. The forecourt makes it easy, and the mistake runs one way.
It happens when routine and the vehicle stop matching. Hire cars, courtesy cars, and vehicles that are new to you. One petrol and one diesel on the drive of the same household. The pumps in a different order on a familiar forecourt. A hurried fill on the way to the nearest station with a train to catch. Precisely the moment it takes place: after years of driving petrol, a driver fills a diesel Volkswagen Passat for the first time. With rain, a call coming in, or a car full of children to deal with, the hand simply does what it has always done.
Next time you fill up in Tadworth: avoiding petrol in a diesel
- A green handle for unleaded and black for diesel is usual in the UK — but not on each forecourt. Trust the label on the pump, not the colour.
- The first fill in an unfamiliar vehicle is the time to check the filler flap — inside it, or on the cap, plenty of motors state the fuel to use.
- Mark your key. In a household with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of meaning to remember.
- It sounds daft and it works: on the first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the petrol pump.
- Thinking about something else is when this becomes an easy mistake to make, so tuck the phone away and keep your mind on the petrol pump.
- Some diesels come with a filler built 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 checking the pump.
- Less petrol makes a thinner mix, and so stop as soon as you realise — while remembering that the next step is unchanged. It's still not to fire it up.
Already put petrol in a diesel around Tadworth?
Then the order of things is short. Don't switch the ignition on, and don't fire it up. Ask the staff to help you roll it away from the pump if you are still on the forecourt, whether that is Texaco or anywhere else. What got in, about how much, and whether it's run: tell us those when you call 0333 366 0103.
Say so if it was AdBlue instead of petrol: it's a separate problem, with its own page for Tadworth, because AdBlue brings corrosion and deposits rather than lost lubrication.
Why one petrol in a diesel job in Tadworth costs more than another
There's no honest single price for this, because the four scenarios above are four separate tasks. What moves the cost is mostly which of them you're in. Where your car is counts too, and whether a technician can safely get to it, after the share of petrol to what that tank takes.
What was put in, how much, and if it's run — three queries our technicians ask before costing, not after, for exactly that reason. Their answers are what turn a range into one firm number.
About Tadworth, briefly
Tadworth is a village in Surrey, situated inland at an elevation of 174 metres, approximately 15.6 miles from London. Tadworth lies near the North Downs, close to neighbouring villages such as Walton on the Hill and Kingswood. Tadworth has a population of around 2092 people, predominantly living in detached houses. Tadworth is also near Kingswood Warren, a wooded area with scenic views.
Fuel drain cover across Surrey, Tadworth included
The vans answering petrol in diesel calls around Tadworth, in the KT postcode area, equally work the places around it, Walton on the Hill, Kingswood and Kingswood Warren included. Our technicians drain wherever the car is — your own drive, a lay-by, a supermarket car park, a forecourt — so it does not have to come to us.
At the pump around Tadworth, right now?
Then, you could not be in a better position. Leave the car switched off, then ring.