What does white smoke coming from a diesel engine mean?

White smoke coming out of a diesel engine can usually be attributed to either over-cooling or a fouled piston ring. Both of these problems result in poor combustion, which creates the white smoke.

White smoke appears when fuel does not fully combust. The unburned fuel forms a “fog,” which is expelled by the exhaust as white smoke. It is normal for a cold engine to create white smoke when it is started; however, the white smoke should not be as apparent after the engine warms up.

If the white smoke persists after the engine warms up, or if it is accompanied by poor engine performance, this indicates that an injector might be worn or faulty.