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Feeling thirsty 

Diesel PumpA faulty fuel gauge can lead you to believe there's more fuel in the tank than you think, as Simon Jinks found out, the hard way

Every time I see a piece of boating advice saying, ‘Ensure you have enough fuel’, it makes me wince. I mean come on, who in their right minds would go out on a trip without enough fuel. Well I did the other weekend, so be warned...

I was working on a six year old 28 foot motorboat and during the initial engine checks the fuel gauge read just over half a tank of diesel. More than enough for the short trip up river that we were planning but I thought we would fill up anyway as I do not like running on half full tanks.

We found the marina fuel pontoon out of action and the next fuel pontoon was understandably crowded with boats queuing. Time to make a decision; the fuel gauge showed well over half full and with the tide in our favour we decided to carry on with the thought of fuelling up on our return.

With the two hours passage up and down the river completed we returned to the estuary for a final run up to cruising revs for 10 minutes after the two hours of low rev work up river. The fuel gauge read just under half a tank fuel, more than enough, or so we thought.

The engine spluttered and stopped

I increased the revs, the bow lifted and the stern dug in and then five seconds later the engine spluttered and stopped. We turned the key again, the engine started but when I put it into gear and gave it some beans it stopped again. It is a horrible feeling, being on a single engine boat and knowing that you are powerless.

I tried again. I turned the key but this time kept the revs at tick-over and the engine kept running. It was evident that it was a fuel problem.

We were about a mile from the fuel pontoon, so we pointed towards home and keeping the boat in tick-over. A passing motor boat heading in the same direction accompanied us back in just in case the engine stopped completely and we needed a tow.

With the fuel gauge still showing just under half, we made it to the fuel pontoon, fuelled up and returned to our berth.

Investigation

On investigation the tank was about a quarter full and the fuel gauge was over-reading by about 20%. Plus the design of the tank was flat like a bar of soap.

So whilst there was still quite a bit of fuel, once it got down to a lower level the fuel would slosh from end to end dredging sediment and sludge from the bottom of the tank and into the filter.

This problem increases as the boat tilted under acceleration. Low fuel levels will stir up fuel in any design of tank, it is just worse in a flat shaped tank.

With partially blocked fuel filters, increasing the revs made the engine hunt for fuel which could not pass through the filters making the engine stop.

Our saving grace was running the boat at low revs so just enough fuel could pass through the filters to run the engine. Needless to say the filters were changed and spares bought to replace the used ones.

It was the first time in 30 years that I had run out of fuel in a boat and frankly I should know better.

  • Keep your tanks topped up to reduce the chance of debris in the filters. This also reduces condensation within the tanks and the resultant water in the fuel.
  • Be aware that fuel gauges are often inaccurate and that boat heel will change where the fuel is within the tank. Boat heel will also stir up debris and can take fuel away from the fuel pipes.
  • Have a plentiful supply of fuel filters and know how to change them If the engine revs start going up and down, reduce revs and if the engine continues running then it is probably a fuel filter problem.

Simon Jinks, RYA Instructor and Examiner

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