Diesel engines are difficult to start in freezing conditions: glow plugs, fuel supply and compression pressures (Siuntio–Veikkola)

A diesel engine struggles to start in freezing conditions when a cold engine does not receive enough heat, fuel or cranking speed. Glow plugs, the battery, the fuel filter and engine compression pressures can all contribute to the same symptom. If the car cranks for a long time, only starts on the second attempt or emits smoke when starting, it is best to narrow down the fault by taking measurements rather than replacing parts at random.

A diesel engine has difficulty starting in freezing conditions when the glow plugs do not provide sufficient assistance

The glow plug heats the combustion chamber before starting and aids the ignition of cold diesel. A faulty glow plug, a fault in the glow plug control system or a problem with the electrical connection may result in prolonged starting, particularly on frosty mornings. The symptom may be mild in milder weather, which is why the problem can easily go unnoticed before winter. We’ll check the glow plug system as part of fault diagnostics.

A cold start also requires sufficient starting speed. If the battery is low, the starter motor will turn the engine too slowly, even if the glow plugs are working. Short journeys, the use of electric auxiliary heaters and freezing temperatures put a strain on the battery. The Automobile Association reminds motorists that a well-charged battery improves cold-weather starting. Read the Automobile Association’s guidance on battery charge levels.

The surest way to identify the cause of a cold start problem is to systematically measure the glow plugs, starting current and fuel supply.

The fuel supply may prevent the diesel engine from starting in freezing conditions

A fault in the fuel supply may resemble a glow plug fault. A clogged fuel filter, air in the fuel system or leaking injectors can make starting difficult, even though the engine turns over normally. In freezing conditions, the cold-weather characteristics of diesel fuel become more pronounced, as paraffin crystals can block the filter and cut off the fuel flow. Neste explains the importance of diesel filterability in cold conditions.

Do not keep trying to start the engine for long periods if it shows no sign of starting. Repeated attempts to start the engine will drain the battery, which may then lead to an electrical fault as well. First, check that there is fuel in the tank and that the car is using diesel suitable for the conditions. When booking an appointment, please let us know at what temperature the problem occurs, how long the car has been standing, and whether starting the engine is easier once it has warmed up.

Compression pressures and measurements determine the cause of a cold start

A diesel engine ignites the fuel using the heat generated during compression. If compression pressures have dropped, a cold engine may be difficult to start, even if the glow plugs and fuel supply are working properly. A potential compression problem cannot be identified simply by reading fault codes; it requires an assessment of the engine’s condition and, if necessary, measurements. That is why we proceed on the basis of the symptoms, rather than relying on a single assumption.

Here at STS Evitskog, we are investigating a diesel car’s starting problem as a whole in Kirkkonummi. Where necessary, we check the electronic control system, the glow plugs, the battery and charging system, and the fuel supply, after which we assess the next steps based on our findings. Regular scheduled maintenance helps to keep filters and other maintenance items in good working order in accordance with the manufacturer’s programme. We also cater for motorists travelling from the Siuntio and Veikkola areas.