Modern fuel has a relatively short shelf life without a preservative. In as little as six weeks modern petrol can start to thicken and block our engines internals. Diesel can suffer from organisms growing inside it, which can also cause a diesel engine to grind to a halt. And no engine, whether it be petrol or diesel, will enjoy the taste of water mixed with its fuel. The issue is compounded somewhat by modern engines, that deliver extremely precisely measured amounts of fuel to minimise the amount of fuel burned during operation. These small, precise parts are certainly more prone to blockage than engines of old, so we need to be extra careful about how we treat fuel that is left in our boats tanks over the winter.