I put 5 litres of petrol in my diesel in Keswick — now what?

By Rambo S, Wrong Fuel Expert at Fuel Fixer International · 30 September 2026

Why five litres of petrol is not a safe amount

The old rule of thumb — that a few litres in a full tank of diesel would be fine — came from older indirect injection engines that tolerated it. Modern common-rail diesels run their high-pressure pumps at tolerances where even a small loss of lubrication causes wear. Five litres in a part-full tank is a meaningful proportion.

The dilution myth

The advice you will find on forums is to brim the tank with diesel and drive it off. It is the single piece of advice most likely to turn a drain into a pump replacement, because it involves running the engine on contaminated fuel for as long as it takes to burn through it.

Twenty litres, ten litres, two litres

The questions come in every quantity, and the answer barely changes. The amount affects how much has to be extracted; it does not change the decision. If the engine has not run, it is a drain. If it has, it is still usually recoverable — which is why the first question on the phone in Keswick is always whether you started it.

Around Keswick

Almost every Keswick call is a visitor. There are so few forecourts in the catchment that everyone uses the same handful, usually in the dark after a day on the fells, frequently in a hire car or a campervan they picked up that week. Late afternoon and evening, heavily seasonal, with a pronounced spike in school holidays and bank holiday weekends.

That applies across the villages we cover, including Wythburn, Scales, Wythop, Setmurthy, Crosthwaite, Ashness, Manesty, Dockray, Skelgill, Uzzicar, Orthwaite and Peter House.

1. Stop. Do not turn the key Whatever else happens, this is the decision that matters. Contamination only travels under power.
2. Resist the urge to move it The instinct is to get out of the way. Unless you are somewhere dangerous, staying put is the cheaper instinct to follow.
3. Safety before diagnosis If you are on a live carriageway, get out and get behind the barrier, and let the police or National Highways deal with the lane first.
4. Phone 01293 248666 You will be asked four questions and given a price and an arrival window. Both are honest rather than flattering.
5. On-site extraction The tank is emptied, the feed lines are flushed, fresh fuel goes in and the system is primed and run.
6. Done, and the waste leaves with us Under a waste transfer note. It is not tipped and it is not sold back to you.

The mechanical reason the advice is always the same

Every drainer tells you not to start the engine, and it is not a sales line. The fuel path runs tank → lift pump → filter → high-pressure pump → injectors, and contamination only moves along it under power. Stationary, the problem stays in the tank where it is cheap to remove. Under power, it spreads into parts that are not.

Borrowdale, Honister and the Whinlatter pass are narrow, steep and busy with walkers. A vehicle stopped on any of them blocks a road with no alternative, and a low-loader often cannot reach where a technician can.

The cost, honestly

People expect the number to depend on the amount of wrong fuel. It barely does. It depends on how far the contaminated fuel travelled through the engine.

More on wrong fuel in Keswick

For coverage by postcode district, see the postcode index; for the roads we cover, the road guides; and for every town and village by name, the area index.

Background reading: Waste carrier registration — GOV.UK.