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Duramax, Powerstroke, RAM / Dodge, Tech Talk

Diesel Smoke Diagnosis – XDP Tech Talk

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A properly running diesel engine should not produce any visible smoke out the tailpipe. If smoke is coming from the exhaust for a prolonged period, it could indicate a more serious problem with your engine. This guide will help diagnose the underlying causes and help you understand what each of these exhaust colors could mean.

Diesel engine smoke typically comes in three basic colors: black, white, and blue. Of course, a small amount during acceleration can be perfectly acceptable on an older diesel engine, so it is also important not to overreact if you see a quick burst of black smoke.


Black Smoke is the most common color emitted from the exhaust pipe of a diesel engine. This often points to an issue with the air/fuel ratio, i.e., too much fuel and not enough air. When diagnosing the problem, the first place to look should probably be the fuel injectors.

Common Causes of Black Smoke:

Damaged, Dirty, or Worn Fuel Injectors
Damaged Injector Nozzles
Injectors Sticking Open Too Long (Common Rail Diesel)
Clogged Air Cleaner
Operating Temperatures Too Cold
Incorrect Injector Timing
Engine Tuning
Malfunctioning Turbocharger
Damaged Intercooler
Incorrect Valve Clearance
Improper Air/Fuel Ratio
Restricted Induction System (Too Small or Kinked Pipe)
Faulty Injection Pump
Damaged/Clogged EGR Cooler
Poor Quality Fuel
Excess Carbon in Intake Manifold
Low Compression
Excessive Engine Sludge Build Up


White smoke often indicates not enough fuel is burning (or not burning any fuel at all) and unburned diesel fuel had made its way through the exhaust completely unused. This can also mean that your vehicle is too cold on start-up or that coolant has made its way into the combustion chamber. Malfunctioning glow plugs during a cold start can be another culprit.

Common Causes of White Smoke:

Damaged Injectors
Incorrect Injection Timing
Low Cylinder Compression
Damaged Rings or Cylinder Liners
Water in the Fuel (Cracked Head Gaskets, Head, or Block)
Damaged Fuel Lines
Low Fuel Pressure to the Fuel Pump
Malfunctioning Glow Plugs
Damaged or Incorrect Fuel Pump Timing


Blue engine smoke is the rarest type expelled from a diesel engine. If your truck is discharging blue smoke, this can be an indication of oil burning in your engine. This can be caused by leaky valves, worn piston rings, or a failure of critical seals. Blue smoke should not be ignored, but instances such as cold weather can make it temporarily appear. A professional can diagnose your engine and figure out exactly where this oil is coming from.

Common Causes of Blue Smoke:

Damaged, Worn, or Sticking Piston Rings
Damaged or Worn Cylinders
Worn Valve Guides or Seals
Faulty Turbocharger Seals
Overfill of Engine with Oil
Damaged Lift Pump
Fuel Mixed in the Oil
Incorrect Oil Grade (Too Thin & Getting Past the Rings)
Cylinder Glaze

No matter the color, excess smoke is not something you want to see. If you are experiencing more than the usual levels expelled out your tailpipe, make sure to shut down the engine immediately. Having the engine properly diagnosed by a professional could prevent any further damage from occurring.


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