Blue Smoke or Oil Smoke

Blue smoke out of the other colors you may see in your diesel engine, is the worst color you want to see. In Non TurboCharged engines, it means the same things it does in a gasoline engine. Either Valve stems, or Piston Rings, or a generally tired engine.

Turbo/Supercharged engines on the other hand, it can be the aforementioned problems, or it can also be something else, the Turbo/Supercharger seals.

In the event your Turbo Seals go, and usually the sign is sudden blue smoke that quickly develops over a short period of time, if the seals get bad enough, and the seal is leaking on the Intake side of the turbo, or the compressor side of the turbo, the engine can very well run away, and destroy itself. I have personally heard of a Cummins Diesel that ran away in this manner and the engine reached over 6,000 rpms estimated before the rods made new windows in the block. It was not the engine's fault, but the turbo that caused it. If you suddenly start seeing blue smoke out of your exhaust, and you are Turbocharged, stop driving the vehicle, and get the turbo rebuilt. The turbo is save-able at this point, however, if you can visually see that the turbine wheels are hitting the housing, or can hear that they are, it is time for a new turbo. See our 'Turbo Charger Maintenance' Article for a how-to on checking to see if you have excessive play in your turbines.