Cold Start

The engine needs a richer mixture. Diesels use glow plugs. Most wear happens in the first minutes. Block heaters warm the coolant or oil in very cold climates and reduce wear and emissions. Thin oil of the correct winter grade reaches bearings faster. Cold starts put a high load on the battery, so weak batteries often fail on the first frosty morning. Starting and driving off gently is better than long idling.

The ECU adjusts fuel and idle until warm.

Hard cold starts can point to battery or sensor faults. Avoid high revs right after starting.