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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: Why does my vehicle go into reduce engine power mode. 2008 Chevrolet Silverado

Hello. I would need to know what code you are getting to know what needs to be done to take care of this. If you are getting a MAF code then the sensor may be failing, but that will not...

Q: Bad catalytic converter and white smoke from tire

Hello. This does sound like a problem related to the catalytic converter being faulty. The smoke from the driver’s side front wheel could be caused by the front driver side caliper locking up. This may make the wheel difficult to...

Q: Diesel poured into a gasoline car

At least you didn't put gasoline into the diesel car. If you did and started the engine, the engine would blow up. Diesel fuel is a lower grade fuel so your engine is probably going to ping. I'd advise draining...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
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.