Understating Why Diesel Engines are Hard to Start in Cold Weather

Attempting to start Diesel engines in cold or sub zero temperatures is extremely difficult and usually an impossible task, unless appropriate accessories has been added to the engine to assist in such starting.

The hard starting problems of diesel engines in below zero / freezing temperatures are caused by two factors. One is the initial cold air being drawn into the turbocharger and compressed into the engine’s cylinder head. The second is the fuel itself, is also cold and this sub zero / freezing temperature fuel is sprayed into the cold engine’s combustion chamber, where it mixes with the cold air drawn thru turbocharger.

Additional problems will result from fact that a cold starting diesel engine needs to reach at least two hundred (200) rpm to develop a four hundred (400) psi compression pressure to sufficiently compress the air to fuel mixture, and thus, resulting in combustion.

These two problems will result in the diesel fuel being sprayed into the combustion chamber, and it will condense on the cold surfaces of the cylinder liners or cylinder block. This liquid fuel will seep through the piston rings, and fall into the engine’s crankcase, diluting the lubricating oil in the process.

Two simple devices can be used to reduce the possibility that these conditions occur. One is by the use of battery heaters and glow plugs. No one device can be used. Usually a combination of several devices will provide an overall efficient starting process.

The efficiency of a battery drops as its temperature drops. A battery that is fully charged at 26 degrees C (80 degrees F) will have its starting capacity drop to approximately forty six percent (46%) available power at 17.7 degrees C below 0 (0 degrees F). Additionally, at this temperature, the engine will be approximately two and a half (2.5) times harder to start at -17.7 C (0 F) degrees due to thicker oil and resistance to movement of internal moving parts. This gets worst at lower temperatures are experienced.

To solve this, one of two common devices is used to heat the battery. One is a padded silicone covered, acid resistant rubber hot pad heater. This operates off of 110/120V and comes in various wattages. The power range can be 60W to 500W, and this can be used to heat the batteries, engine oil pan, fuel tank, hydraulic tank, and the water tank.

The other device that is typically used in conjunction with the hot pad is the glow plug. This is an internally fixed low voltage heating element that is fitted directly into the combustion chamber. When this is switched on, it can take up to two minutes to heat up, however, by that time it has reached approximately 700 degrees C (1652 degrees F) and the combustion chamber is hot enough to prevent the condensing of the diesel fuel, and thus, ignition is guaranteed.

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