Skip the auto shop - Our mechanics make house calls

Q: Why Do Diesel Engines Give Off so Much Smoke?

asked by on

Why do diesel engines give off so much smoke?

A: The smoke you see is made up of the visible...

The smoke you see is made up of the visible particulates that are emitted as a normal part of the combustion process of a diesel engine. There are other non-visible emissions in the exhaust also, like nitrous oxide. Diesel fuel has more energy potential for a given volume of fuel than gasoline, which is one of the reasons why the fuel economy of a diesel powered vehicle is better than a gas engine vehicle. The energy potential is visible when you compare samples of diesel fuel and gasoline. Gasoline flows very thinly, while diesel feels oily and heavier. A very rough analogy is it’s kind of like burning big pieces of wood in your fireplace instead of smaller branches. Because of Diesel’s heavier nature, essentially what you’re seeing is the residue leftover from combustion, similar to the ash left after a wood fire goes out. The reason you don’t see smoke from modern diesel powered cars and light-duty trucks is because manufacturers are required to add exhaust particulate traps and catalytic systems downstream of the engine to process particulates and other emissions into less toxic gases.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Diesel in gasoline tank

Yes, this can happen from time to time. The entire fuel system will need to be drained and flushed, the fuel filter, which is in the fuel tank as part of the fuel pump, may need to be changed. The...

Q: Exaust system

Hello, thank you for writing in. While most components in the exhaust system have their own name, the piece of pipe that connects the exhaust manifold crossover pipe to the catalytic converter is considered part of the converter, or known...

Q: Coolant is leaking also smoke is coming from engine.

If the white smoke is coming from the engine / engine bay, then it's possible that the leaking coolant is coming into contact with hot engine and/or exhaust components and causing the smoke. If the white smoke is coming from...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.