September 2, 2021

Diesel Engine Questions and Answers – Part 2

Written By: ProSource Diesel

At ProSource Diesel, we like our customers to be informed about diesel engines, diesel parts, and how these engines work. There are a number of diesel terms, concepts, and diesel engine parts that may not be familiar to new owners or those who are only familiar with gas engines.

This is part two of our list of common diesel engine questions and answers to help you get up to speed. Diesel Engine Questions and Answers – Part 1 was posted last month.

Q: What causes black smoke from diesel engines when accelerating?

A: You’ve probably seen clouds of black smoke coming out of the exhaust of a diesel truck, especially if the truck is hauling or towing a heavy load or is under hard acceleration. The black smoke you see is elemental carbon that results from the incomplete combustion of diesel fuel.

The primary cause of black smoke from diesel exhaust is over-fueling. Over-fueling is caused by worn diesel fuel injectors. Excess fuel leaks into the combustion chamber and is not burned off.

Diesel engines are not inherently capable of efficiently burning excess fuel. This means that excess fuel is wasted and comes out of the exhaust only partially combusted. Other possible causes for black smoke include the following:

  • Dirty air filters
  • Excessive oil consumption due to worn parts
  • General engine wear
  • Excessive engine deposits

Q: What is a diesel engine?

A: A diesel engine is an internal combustion engine that uses compressed, high-temperature air to ignite diesel fuel as it’s injected into the cylinder. This is different from a gas engine, which uses a spark to ignite fuel.

Because diesel engines generate a large amount of torque, they are the primary engine type used in large freight trucks, locomotives, and large marine vessels. Diesel engines are also available in just about every class of passenger vehicle, including cars, trucks, SUVs, and vans.

Q: When to use a block heater on a diesel?

A: The exact temperature where you might need to use a block heater can vary. The main thing you should consider is how cold it will be at night or in the early morning hours if you need to use your truck right away in the morning. Modern diesel engines can usually start at temperatures as low as -22 degrees Fahrenheit, but it can cause strain on the engine.

Generally, it’s a good idea to plug in your block heater when the temperature is 5 degrees Fahrenheit or lower. Remember, if you need to drive your truck right away in the morning and the overnight temperatures will drop below 5 degrees, you should plug in the block heater in advance.

Q: Why do diesel trucks have two batteries?

A: If you’re a first-time diesel truck owner, you might be startled to find two batteries under your hood when you look for the first time. Yes, it’s true, diesel trucks have two batteries versus most gas-powered engines that have only one.

Diesel trucks have two batteries because they need more power to turn over. Diesel engines need a high-resistance load to successfully start. To put it simply: diesel engines require nearly twice the amount of energy to start versus gas engines, and a second battery provides this extra energy.

Q: Why a diesel won’t start when cold

A: It’s not universally true that diesel engines can’t start when the weather is cold. As previously mentioned, most modern diesel engines can still start in very cold temperatures even without a block heater.

However, it is true that the process of starting a diesel engine is hampered by cold temperatures. This is due to the fact that diesel engines use compressed, high-temperature air to start versus the spark that starts gas engines. As you might imagine, this process is not as easy when the temperatures are very cold. Diesel engines don’t have spark plugs, but rather glow plugs.

These plugs heat up the inside of the cylinders, which allows the diesel ignition process to go smoothly even without a block heater. So, if your diesel won’t start when it’s cold, it’s very possible that your glow plugs have gone out. Glow plugs should generally be changed every few years. Another tip is to allow your glow plugs to heat thoroughly a couple of times before trying to start your engine in cold weather.

Q: What causes a runaway diesel?

A: Runaway diesel happens when a hydrocarbon or flammable vapor gets into the air intake system and the engine begins using it as an external fuel source. This causes the engine to start running off these vapors, which leads the governor to release less diesel fuel.

Eventually, only the vapors are running the engine. If the runaway diesel isn’t stopped immediately, the engine will overspeed, the valves will bounce, and flames can get through the manifold. The flames can ignite more flammable vapors and cause a catastrophic reaction.

A large-scale example of a runaway diesel is the Deepwater Horizon explosion that happened in 2010 in the Gulf of Mexico. The worst part about a runaway diesel is that it can happen within 3 to 12 seconds of low concentration gas levels getting into the engine intake.

Count on ProSource Diesel for a wide selection of diesel truck parts, including Cummins parts, Duramax parts, Powerstroke parts, and all types of diesel performance parts for upgrades and repairs. ProSource is where the diesel repair shops shop for diesel parts.

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