Why does my diesel oil look black right after an oil change? This is a common question from people who own diesel vehicles. There are a few reasons why this happens that we will discuss here.
- High Compression
Diesel engines use compression to ignite the fuel. High compression is used in diesel engines to optimize torque and horsepower while also minimizing emissions. Because compression is so high in diesel engines more blow-by occurs. Blow-by is when combustion gases bypass the piston rings and end up in the oil. This results in soot, or carbon, which makes the oil black. Soot is normal in diesel engines.
- Emissions system/EGR
The EGR (exhaust gas recirculation) also plays a role in higher soot or carbon build up. The EGR system recirculates some of the exhaust back into the air intake system and into the combustion chamber for better fuel efficiency. Doing this helps reduce the amount of exhaust emissions exiting the tailpipe. When the exhaust gas reenters the intake system some contaminants enter as well causing the engine oil to be darker in color. This is also considered normal for diesel engines.
Here at Rogers Mobile Lube & Tire, we use Amsoil Synthetic’s Signature Series engine oil. Amsoil is high in detergent that keeps the carbon suspended in the fluid, so it does not build up on engine parts. Keeping carbon particles suspended helps them reach the filter where they are trapped.
We also use Amsoil oil filters that are 99% efficient at 20 microns filtering out nearly all contaminants large enough to damage your engine. To read more about Amsoil and its technology click the link here. Even with this superior filtration technology, when we drain the old black oil from your diesel engine, there are small, harmless particles of soot that still coat the internal parts of the engine. When we install the new oil these particles will then be suspended in the new oil giving it the dark color almost immediately. This is a totally normal and expected phenomena.
Authored by Steven H.