What to do with Boat Fuel in Winter

What to do with Boat Fuel in Winter

For many New Zealanders, the winter months mean less time on the water. Boats can lie idle, sometimes for many months, and as the old saying goes, idleness is the parent of mischief. Experienced boater John Eichelsheim offers some useful tips to keep things shipshape fuel-wise if you haven’t used your boat over the winter months…

In some countries, laying up the boat for the long winter months is routine. The winterising process can involve storing the vessel under cover ashore, draining all the fluids and removing any gear or furnishings that might deteriorate in sub-zero temperatures. Wise owners visit their vessels regularly through the winter to check all is well and many install heaters or dehumidifiers to moderate the effects of the cold and damp.

Two of a boat's essential elements - batteries and fuel filters - should be easy to get at and check.

Two of a boat's essential elements - batteries and fuel filters - should be easy to get at and check.

In New Zealand, true winterisation is not normally required, although if you are laying up your boat for a long period, draining the fluids is recommended, just as you would when preparing a car for long term storage.

Stale fuel

For petrol-powered craft, one of the things to consider if you are not using your boat for a while is the condition of the fuel. Petrol deteriorates quickly, becoming ‘stale’ after just a few weeks.

Petrol is a complex mixture of different components, each with specific properties that contribute to its performance. These components evaporate at different rates, adversely affecting the way the fuel performs over time.

Problems with stale fuel are especially common at the beginning of a new boating season, when the boat is used for the first time in months. If the fuel in the tank is old, you can expect trouble. In most cases, the effects are minor: the engine refuses to start or run properly and the voyage is aborted before any damage is done. Sometimes, though, degraded fuel can cause more serious problems requiring costly engine and fuel system repairs, or else result in breakdowns at sea.

Petrol becomes ‘stale’ when many of the volatile components have evaporated. The lighter components, which evaporate first, are the elements that provide the higher octane needed for cold starting. It’s a bigger problem in cold weather, too.

Stale fuel also forms deposits of gum and varnish in the fuel system, which eventually affect its ability to deliver fuel. This problem is accentuated if you use two-stroke fuel-oil mixes; the fuel evaporates, but the oil does not, meaning it becomes more concentrated so that it fouls spark plugs and clogs fuel lines.

Blended fuels containing ethanol are another complication. Some fuel retailers sell E10 ‘bio-fuels’ containing up to 10% ethanol. Ethanol evaporates faster than the other components, quickly altering the ratio in the remaining fuel. It should not be stored for more than a couple of weeks.

Avoid bio-fuels which contain ethanol. 95 premium petrol is always the best option for outboards.

Avoid bio-fuels which contain ethanol. 95 premium petrol is always the best option for outboards.

Actually, ethanol mixes are not recommended by most outboard manufacturers for a variety of reasons. Ethanol-blended fuels are hygroscopic, meaning they absorb water. Ethanol mixes perfectly with water and, in a process called phase shifting, the solution separates out and eventually settles to the bottom of the fuel tank as a corrosive slurry.

Sucking this slurry through the engine fuel system can cause major mechanical issues – even a water separating filter may not catch it since the water-ethanol solution is lighter than pure water.

Ethanol is also a natural cleansing agent which can loosen contaminants that have built up in the fuel system. These can quickly clog the filter. Ethanol-blended fuels also dissolve rubber components in the fuel system, particularly in older engines. Modern two- and four-stroke outboards can run E10 fuel, but many engine manufacturers, marine mechanics and boat builders don’t recommend it.

Oxidation

Petrol, even when kept in sealed containers to reduce evaporation, still oxidises to form peroxides. Peroxides attack metal and rubber, causing seals and hoses to break down and corroding copper parts in fuel pumps. It usually takes a few months for this to become an issue and most fuels now contain anti-oxidants which slow the process, but oxidation is worse if the fuel is exposed to UV light – so don’t store fuel in the sun.

Problems associated with stale fuel are more acute than they used to be, since petrol is now universally unleaded. Unleaded petrol degrades much faster inside the fuel tank than leaded petrol used to, typically within a month. Evaporation happens more quickly in warm weather.

Fuel tanks are equipped with breathers to vent evaporated gases. However, tote tanks have breathers that can be closed off, slowing the rate of evaporation. It pays to close off the breather vent on tote tanks when the boat’s not being used or tote tanks are in storage. However, in warm weather or direct sunshine, tote tanks can swell up with the pressure of evaporated petrol compounds inside the tank, so store tote tanks in a cool place whenever possible.

Tote tanks should be stored out of the sun over winter and have their breather vents closed.

Tote tanks should be stored out of the sun over winter and have their breather vents closed.

Keeping it fresh

The easiest way to avoid the problems caused by stale fuel is to use fresh petrol. But nobody wants to dispose of half a tank of unused fuel, especially if you carry a couple of hundred litres under the floor. That’s a lot of money down the drain and anyway, disposing of petrol is not easy – pouring it down the drain is definitely not an option!

Drains are not a viable option for disposing of old fuel - you are far better off syphoning it into your car.

Drains are not a viable option for disposing of old fuel - you are far better off syphoning it into your car.

One solution is to top up a partly full tank with fresh fuel and use it immediately. Fresh fuel restores the volatile components that have evaporated. Even topping it up by a third will do the trick. Using a fuel stabiliser protects the fuel system from corrosion and the formation of varnish and gum, but stabilisers don’t slow the evaporation of volatiles.

If you know you won’t be using the boat for a couple of months, you are better off emptying it of fuel (as much as possible, anyway – you can top it up with fresh petrol before your next trip), perhaps decanting the old fuel into your car.

Water in the fuel

Water in the fuel is another problem most boaters will experience at some point, most often when the fuel has been stored for some time or the boat hasn’t been used in a while.

Some water finding itself into the fuel tank is unavoidable. Air is full of water vapour which condenses inside the fuel tank, but the problem is worse if the tank is only half full.

Water in fuel can cause costly damage to your engine, or at the very least adversely affect its performance. Water in the tank can also encourage bacteria and algae to grow. Most boat fuel systems incorporate one or more inline filters designed to prevent debris and other contaminants reaching the engine; some inline filters can also deal with small quantities of water.

The best protection is a water separating filter between the fuel tank and the engine. Many of us are familiar with these from our own boats and most have a clear bowl at the bottom which allows you to see any water the filter has extracted from the fuel. It’s not unusual to empty water from this bowl from time to time, but if you are emptying it often, you have a water in fuel problem which needs to be addressed.

It doesn't matter what size your vessel is, having a decent filter in the system will help eliminate water condensation and contaminants in your fuel.

It doesn't matter what size your vessel is, having a decent filter in the system will help eliminate water condensation and contaminants in your fuel.

Siphon all the fuel (including the water that has separated out and sunk to the bottom) from your tank and when the tank is empty, inspect it and its peripherals (hoses etc) carefully for damage, corrosion or evidence of leaks. A serious water-in-fuel problem is usually the result of water getting into the fuel tank from outside. Repair or replace the fuel tank and peripherals as required.

Once you are satisfied with the fuel tank’s integrity, fill it with fresh fuel and always keep it near full to reduce the amount of water condensing from the air inside the tank. Don’t overfill the tank though, because the fuel expands and contracts with changes in temperature. Fill it too full and it will overflow on a warm day.

Fuel System Trouble-Shooting

Mechanics say 95% of the problems with outboard motors are fuel related.

Dirty or stale fuel

If there’s a chance fuel has become stale or contaminated, drain it from the tank (you can use a siphon juggler to empty underfloor tanks) and replace with fresh fuel.

Filters

Fuel filters get dirty quickly and should be replaced once a year at least. If you experience poor starting, power loss/cut-outs or power surging, try replacing the fuel filter.

Fuel lines

If the fuel line is crimped, collapsed or split, fuel may not be flowing correctly. Check the whole length of the line for problems.

Fuel left in the fuel line can gum up over time. Residue in the line can potentially damage the engine next time it is run, so if you can’t remove debris from the fuel line, replace it.

Primer bulb

The primer bulb doesn’t last as long as other parts of the fuel system. Bulbs perish, wear out and lose pressure. Replacing them could be a simple fix to a fuel problem.

Blocked vents

A blocked fuel tank vent, or in larger boats with under-deck fuel tanks, a sag in the fuel line, could be causing the problem. Check a sagging fuel line isn’t causing fuel to puddle and for boats with tote tanks, make sure the vent is open.

If your vent has a screen, clean out any debris with a wire brush or replace it if the mesh is corroded. Also check that the breather vent isn’t letting in water.


August 2020 - John Eichelsheim
New Zealand Fishing News Magazine.
Copyright: NZ Fishing Media Ltd.
Re-publishing elsewhere is prohibited

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