Why Does a Diesel Engine Shake at Idle When Cold?
2 Answers
Diesel engine shaking at idle when cold occurs because the temperature inside the engine is insufficient, and both the fuel and lubricating oil are not warm enough. Therefore, during a cold start, more fuel should be injected to meet the power requirements. The larger the spark plug gap, the smaller the ignition energy. At low temperatures, fuel atomization is poor, requiring higher ignition energy. Over prolonged use, the spark plug's ignition gap tends to widen, leading to reduced ignition energy, which affects performance and causes the vehicle to shake. Diesel engines and gasoline engines share fundamentally similar structures, including the cylinder block, cylinder head, piston, valves, connecting rod, crankshaft, camshaft, and flywheel. However, the former operates by compressing and igniting diesel, while the latter ignites gasoline—compression ignition versus spark ignition being the fundamental difference between the two.
I often encounter this issue where many diesel vehicles shake like a tractor on gravel roads during winter starts. The root cause is poor fuel atomization when the engine is cold—thick and sticky like poorly stirred porridge. Aging injectors spray fuel unevenly, leading to unstable combustion and inevitable shaking. The intake system also tends to cause trouble; a dusty or dirty mass airflow sensor fails to read the accurate air intake, causing the control unit to issue incorrect commands. Additionally, worn engine mounts with hardened rubber can't dampen vibrations effectively. I've seen many cars improve significantly after replacing injectors or cleaning the throttle body. Regular use of anti-freeze additives for fuel system maintenance and periodic checks on mount lifespan can reduce such annoying occurrences. Especially for northern drivers, it's crucial to warm up the engine for a few extra minutes before driving and avoid rushing to accelerate or add load.
