Diesel Car Smoking? What Black, White and Blue Smoke Mean

The colour of the smoke is the first clue to what is wrong with a diesel engine. It does not prove which part has failed, but it tells you where to look before you spend money on parts.

Black smoke

Black smoke means too much fuel for the air available. A leaking or badly spraying injector is a common cause, but so are a blocked air filter, a boost leak or turbo problem, and a faulty EGR valve. Check the simple things first. If the air side is fine, the injectors should be tested.

White smoke

White smoke, especially on a cold start, usually means fuel is going through the engine without burning properly. Worn injectors, weak glow plugs and low compression can all do this. White smoke that smells sweet and does not clear when the engine is warm can be coolant, which points to a head gasket problem and not the injectors.

Blue smoke

Blue smoke usually means the engine is burning oil. Look at the turbo seals, valve stem seals and piston rings. Injectors are rarely the main cause, so replacing them is unlikely to cure it.

Will a smoking diesel fail the NCT?

It can. Heavy smoke often means high emissions, and that is a common reason for a diesel to fail. Our partners NCTPass, in the same building, can carry out a pre-NCT check before your test.

How we find out if it is the injectors

We test diesel injectors and high-pressure fuel pumps on dedicated test benches, so you get a result in place of a guess. If an injector is out of specification we can recondition it, or supply a new one from brands such as Bosch, Denso, Delphi and Continental.

Testing starts from €80 and injector reconditioning from €140. Reconditioned parts have a 1-year, parts-only, unlimited mileage warranty.

Call 085 200 9922 or request a quote. Diesel Injector Repair, Unit 6, 1st Floor, Old Quarry Campus, Blanchardstown, Dublin 15, D15 HX03.