Reading Diesel Smoke Colors
A diesel engine in optimal operating conditions should not release any smoke. A short puff of smoke immediately after placing the engine under a load can sometimes be acceptable. This is due to the time that lapses before the airflow produced by the turbo charger is able to match the volume of diesel injected into the cylinders. However, this only applies to diesel engines using older technology. With newer engines, you should not see any smoke.
In most cases when a diesel engine is smoking it's an indicator that action should taken otherwise service life will be considerably shortened. Visible smoke from a diesel engine is a sign that something is wrong. The color of the smoke released from the engine can assist in diagnosing the problem. There are three basic types of smoke that can be identified by color - black, white, and blue.
BLACK SMOKE is the most common. It indicates poor or incomplete combustion of the diesel fuel. This could be caused by:
- Timing issues
- Worn injectors due to over-fueling
- Injectors sticking open too long
- Faulty turbocharger causing a mismatch between air flow and fuel
- Valve clearances
- Low cylinder compression caused by sticking piston rings or worn components
- Dirty air cleaner, other air restrictions
- Carbon clogging intake manifolds
- Poor quality fuel that doesn’t burn properly
- Excessive carbon builds up in exhaust system causing lack of air flow
BLUE SMOKE is a sign that oil is burning. Here are possible reasons why this could be happening:
- Valve guides or seals are worn
- Grooved cylinder walls or worn cylinder rings
- Cylinder glaze, lack of crosshatching in cylinder walls
- Piston ring sticking
- Faulty turbocharger seals
- Incorrect grade of oil
- Oil contaminated with fuel causing incorrect viscosity
Blue smoke is always more evident on a cold start and reflects a lack of oil control. Carbon deposits around piston rings or cylinder glaze can be a sign of ring wear or carbon that has built up in the machined cylinder crosshatching. This can cause a smooth surface in the cylinder walls, allowing oil to pass by the piston into the combustion chamber. Crosshatching in the cylinder walls is designed to help create an oil seal, but the grooves can become smooth when impacted with carbon. <P>
WHITE SMOKE occurs when raw diesel comes through the exhaust without being ignited. White smoke can occur when water enters the combustion spaces. Here are a few possibilities that can cause white smoke:
- Faulty or damaged injectors causing severe over fueling
- Incorrect injection timing caused by worn timing gear or slipped crankshaft keyway
- Low cylinder compression due to leaky or broken valves, stuck piston rings, cylinder and/or ring wear, or cylinder glaze
- Cracked cylinder head
- Cylinder head gasket is breached
- Cracked cylinder block
Although the color of smoke being released from the engine could help indicate possible issues your engine is experiencing, we always recommend having a certified technician inspect and run a diagnosis to prevent further complications. Our team is standing by should you ever need assistance!
Written by Scott Foster