Starting a Generator in Cold Weather

At low temperatures, for example −18 °C, a generator that runs without problems in summer may fail to start on an automatic start command. The main causes are a battery whose capacity drops in the cold and a fuel filter clogged by wax (paraffin) formation.

Low temperature affects a diesel engine at four points: oil, fuel, battery and combustion. In this article we go through each of them, and winter preparation, in turn.

How does cold strain the engine?

The oil thickens. The engine turns over less easily. The starter motor draws more current. Lubrication is delayed in the first seconds.

The battery weakens. A cold battery can deliver less cranking current. So just as the engine demands more current, the battery supplies less. We cover the battery in a separate article: why does a generator battery go flat.

The fuel gels. The wax in diesel fuel starts to crystallise below a certain temperature. First the fuel turns cloudy, then the crystals clog the filter. The temperature at which the fuel causes problems depends on its cold-flow properties.

Combustion gets harder. A diesel engine heats air by compressing it and ignites the fuel with that heat. In a cold block, the end-of-compression temperature drops. Without preheating, combustion may not start; even if it does, white smoke and rough running appear in the first few minutes.

Measures

Measure	What it does
Block heater (jacket water heater)	Keeps the coolant and the block warm; makes first start and load acceptance easier
Preheating (glow plugs / intake air heater)	Heats the combustion chamber or intake air before cranking
Winter diesel	Pushes wax crystallisation down to a lower temperature
Fuel filter / fuel line heater	Prevents gelling in the filter in very cold regions
Oil of the right viscosity	Keeps it fluid in the cold; chosen from the engine manufacturer’s table
Correct antifreeze mix	Prevents freezing and corrosion
Battery with adequate CCA, battery heater	Maintains cranking current in the cold
Canopy and room measures	Limit cold airflow and snow ingress

On standby sets that must come online automatically in cold climates, a block heater is an almost standard option. The heater runs on a thermostat and is fed from the mains. If the mains fails, the heater stops too, but the engine stays warm for a while.

Why start in autumn?

The worst time to prepare for winter is the first hard frost. Winter diesel must go into the tank before the first cold spell; if the tank is full of summer fuel, the new fuel won’t mix in until most of the old fuel has been used. Batteries show their weakest side on the first cold morning; test them at the end of summer and you have time to replace them. The block heater element and thermostat should also be checked before they are really needed, not while the set is warm. A practical rule: finish your winter check before night temperatures in your area drop below zero.

Antifreeze: not just about freezing

The antifreeze mix is set for the lowest temperature expected in the area. Check the mix ratio with a refractometer. In systems that are topped up with water, the ratio drops over time. A frozen block can crack. Antifreeze also provides corrosion protection, which is why it is used in hot climates too.

Canopy and generator room

• Snow and ice can block the air inlet and outlet louvres. When the set runs, it overheats.
• Wind driving cold air straight onto the radiator delays the engine reaching operating temperature.
• The exhaust outlet must not fill with snow.
• An enclosed room needs ventilation in winter too. Don’t close the louvres because it’s cold; the set needs air when it runs. For room design, see our article on generator room and installation.

Starting and loading in the cold

• On first start, white smoke for a short time can be normal. If it persists, look for a low-load or fuel problem.
• Running at low load for long periods does not bring the engine up to operating temperature. Soot and oil build up.
• Without a block heater, the set should not be taken to full load before the engine has warmed up a little. On automatic standby sets this isn’t possible, which is why the block heater matters.
• On test runs, run the set on load and long enough for the engine to reach operating temperature.

Common mistakes on site

• The block heater fuse has blown. Everyone thinks the thermostat is working; the block is ice cold.
• Going into winter on summer fuel. The tank was filled in autumn, and the filter clogs at the first hard frost.
• Mixing petrol into the fuel. Lubricity drops, and the injection system can be damaged.
• Not measuring the antifreeze ratio. A system topped up with water for years freezes in the first harsh winter.
• Long, back-to-back cranking. The battery goes flat and the starter motor overheats. Wait between attempts.

Winter preparation checklist

• Is the block heater working, and is the block warm?
• Has the preheating system been tested?
• Is there winter diesel suited to the area in the tank? Is there water at the bottom of the tank?
• Are the fuel filter and water separator new?
• Is the oil viscosity right for the cold temperatures?
• Has the antifreeze ratio been measured?
• Has the battery been load-tested, and is the charger working?
• Are the louvres, air paths and exhaust clear of snow and ice?
• Has the set been tested on load?

In cold regions, you can use the fuel consumption calculator to plan fuel consumption and tank requirements.

Next step

Winter preparation should be done in autumn as part of scheduled maintenance. For the scope, see our scheduled maintenance page; for cold-climate options, contact us.