Petrol Fuel Tank Cleaning

When we purchased Bandit in January 2016, we found that both the port and starboard petrol tanks contained very bad fuel that had been sat there for a good number of years. Due to this, the engines were only just in working order. They would not start and when they did finally fire, they ran awfully. We pumped all of the petrol out in February 2016 from both tanks and disposed of it before refilling both tanks with fresh petrol. Although this cured the engine starting issues, we've recently discovered lots of debris in the starboard tank only. The port tank is perfectly clear and causes us no issues.

We've spoken to a local engineering company who say that this build up of debris in the starboard tank is 'petrol varnish'. This varnish looks like little stones and flakes that cover the entire of the bottom of the tank.
Debris in the starboard fuel tank after petrol fuel pumped out

Now, why is this a problem? This debris keeps getting sucked up through the fuel system and is blocking the fuel filters every time the bow of the boat raises up as Bandit gets up to speed. This restricts the fuel flow to the carburettor and the engine stalls. We plan on heading out to The Wash in the next few months so we need to ensure the fuel system is 100%.

We've organised for our local engineering company to clean out the tank. However, this was not as straightforward as we'd hoped. Due to insurance and safety reasons, nobody will pump out petrol from the tank as it's highly explosive. We decided to take the risk and pumped the starboard tank out ourselves into fuel cans until the entire tank was empty. We then put 30 litres of red diesel into the tank as the engineering company are able to flush the tank round with diesel only. The idea is that they'll insert one tube into the tank, suck out the diesel, run it through a large filter which will catch the debris and then pump the diesel back into the tank through another tube. This will go on for a couple of hours consistently until all the debris from the tank has been filtered out. They use a very strong pump so they'll be able to blast off the debris from the bottom of the tank if they need to using the diesel. They'll then pump out that filtered and clean 30 litres of diesel back into cans and we can use it for our diesel heating which is in a separate fuel tank.
Our petrol tank now 1/8 full of red diesel

We took about 60 litres of petrol out from the starboard tank. Apart from the debris, the petrol itself is perfectly good so we purchased a 'Mr Funnel Fuel Filter Funnel' which catches any debris and water while we refuelling. This funnel was £20 but was well worth the investment as we simply put the 60 litres of petrol back into the port fuel tank through this filter to ensure any debris was not put straight back into the fuel system. It worked a treat and works incredibly well. We did a test where we filled the funnel with water - not a drop passed through! We also borrowed the marina's compressor and blew air through the entire fuel system (where we could and where was safe) to blow out any debris stuck in the fuel lines. This ensures we will be 100% problem free from now on...fingers crossed!

Total cost:
30 litres of red diesel @ 0.75p per litre: £22.50
Fuel tank cleaning service: £250
Petrol refueling: 60 litres @ £1.45 per litre: £87
TOTAL: £359.50


  1. It was really insightful.
    Thanks for such a nice content.
    BTW if anyone interested more have a look batterymodeon thanks

  2. Hi,

    I'm having a problem with my engines where they run... ok, until you try and throttle up and then the bow goes up and they die.

    It's this the sort of problem you had? Did the clean solve the problem?


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