Black smoke - too much fuel or too little air
Black smoke is soot from fuel that has not burned completely. A bit of black smoke when accelerating hard on an older diesel is normal. Constant or thick black smoke is not.
- Clogged air filter.
- Leaking or worn nozzles — they spray more or spray poorly.
- The turbo does not give pressure — sleeve leakage, stuck geometry (P0299).
- EGR valve stuck open — exhaust gases replace air.
- Defective flow meter (P0101).
Black smoke fills the DPF filter quickly (P2463), so don't put it off.
White smoke - water or unburnt fuel
White vapor when cold that disappears after warming up is normal - this is condensation in the exhaust. It is a concern when:
- The white smoke stays on a warm engine and smells sweet — antifreeze burns in the cylinders. The most common reason is burnt head gasket or a cracked head.
- The white smoke smells like oil and stings the eyes — fuel does not burn: faulty glow plugs, bad nozzles, low compression or injection timing problem.
Blue smoke - burning oil
Bluish smoke with the smell of burnt oil means that oil is entering the combustion chambers or the exhaust.
- The turbo is leaking oil — worn seals or bearings. There is often oil in the intercooler as well.
- Worn segments or cylinders — the engine "eats" oil, smokes more under load.
- Worn valve seals — blue smoke is strongest after ignition or after long idling.
- Overfilled oil or blocked crankcase ventilation.
When to stop
- The smoke is very thick or comes suddenly
- The engine loses antifreeze or overheats
- The oil level drops quickly — or, conversely, rises (fuel or antifreeze in the oil)
- The engine begins to "accelerate" revolutions by itself
In these cases, do not drive - bring the car to a service center. Diagnostics shows where the problem is before it becomes expensive.