THE storage life of petrol in fuel tanks is one month, according to the experts at BP Australia.
They say this can be extended by topping up with one-third of fresh fuel, which restores the volatile components that have evaporated - however this is not a foolproof strategy for engines that are used intermittently.
They suggest using a fuel that contains anti-oxidants, metal deactivators and corrosion inhibitors to protect metal surfaces.
When preparing to store a boat for extended periods (two months or more), it is best to remove all fuel from the tank. If it is difficult or not possible to do that, maintaining a full tank of petrol and including a fuel stabiliser to provide stability and corrosion protection is recommended.
A partially-filled tank is not recommended because the void above the fuel allows air movement that can bring in water through condensation as the temperature cycles up and down. This condensation can potentially create operational problems.
When two-stroke fuel is mixed correctly, it has the same storage requirements as petrol. Problems arise when excessive two-stroke oil is added. Under this condition, the oil may separate from the fuel.
Diesel is not a volatile fuel, therefore it does not suffer from starting issues or from the evaporation that petrol does. The main issue with diesel fuel in storage is the formation of gums and sediments that can block filters. Moisture from condensation will create a favourable environment for fungus and bacteria which degrade the fuel. The solution is treatment with a biocide every six months when storing for lengthy periods.
Regular unleaded with up to 10 per cent ethanol has an equivalent storage life to regular petrol. As with regular petrol, when using an engine after a period of storage, always top up with a third of fresh fuel first. With ethanol blends, this will remove trace water and dry the system out as well as freshening up the old fuel.
Phase separation is when water contaminates the fuel tank or fuel system, causing the ethanol content to separate from the regular petrol.
The level at which phase separation can occur is determined by a number of variables, including the amount of ethanol, the composition of the fuel, the temperature of the environment and the presence of contaminants. It is very important that the system is inspected for significant quantities of water in the tank before fuel with ethanol and to limit exposure of the fuel tank to excess water.
If phase separation has occurred, you need to remove all water from the system and replace the fuel otherwise engine problems could occur.
Info: BP Lubricants and Fuel Technical Helpline on 1300 139 700.