Each year people ask me about how to start their Mercedes diesel engines in cold weather. I usually end up dispelling myths in addition to giving advice. I decided to write an article to look at some of these myths and back up some good advice with facts about how the starting systems in these cars are designed to operate.
For simplicity, I will use a 1983 300D Turbo diesel (123.133 with OM617a) as a basis for this article. The same theory and functions apply to a wide range of Mercedes diesels from the 1970s through the 1990s.
Myth: “When the preglow indicator goes out, the engine is ready for starting”