Most diesel engines need a cold starting aid. In some cases extra fuel is injected directly into
the combustion chamber, which has the effect of increasing the compression ratio. In other
cases the injector pump has an override device which allows extra fuel through the injectors.
This Lucas Thermostart, fitted in the air intake, warms the air reaching the cylinder and helps the engine start in cold weather. A small quantity of diesel, released through a ball valve which is opened by a heater coil, is then burnt by an electric igniter coil. 1 Fuel inlet. 2 Body. 3 Electric terminals. 4 Heater coil. 5 Igniter coil. 6 Igniter shield. 7 Insulating bush. 8 Needle valve stem. 9 Ball valve.
Many engines have electric glow plugs in the combustion chamber area to heat and ignite the air fuel mixture. Others have electric inlet manifold heating elements which warm the air flowing in. This is sometimes combined with the introduction of fuel into the manifold. This burns in the manifold, warming the engine and helping it to start.
Occasionally, if the engine is fairly old, a small dose of quickstart squirted into the inlet manifold can help. Some manufacturers specifically ban this, as it can build up in the exhaust system and explode, destroying the exhaust when the engine starts.
Valve lifters (decompression levers) are fitted to many smaller engines, and are obligatory for a hand start. These open the exhaust valves, relieving compression. This enables the engine to be turned by hand. As speed is built up the valves are closed and the normal compression cycle begins.
An engine may start easily in summer without any cold start aid, but if it does not it is better to use the cold start procedure to ensure a quick start rather than risk draining the battery by repeated unsuccessful attempts.