Diesel Vs. Conventional Oil: What's The Real Difference?

An oil change is a great starter task for anyone learning about car maintenance, but picking the right oil for the engine to is just as important as technique, especially when faced with deciding whether to use diesel or conventional engine oil.

Much like the fuel you fill into the tank of a diesel or gas car, the engine oil you use to lubricate the motor is also subtly different. Each oil is engineered to optimize the performance of a diesel or gas engine through its makeup.

While the basic composition of the two oils is similar, qualities like the viscosity of the oil and the additives used vary between the two products. So, to ensure you're using the right oil for your beloved project car, we've rounded up the main differences between diesel and conventional engine oil.

Because most of us drive conventional gas cars, we'll start with the engine oil we'll all be most familiar with. Conventional engine oil is made from a base oil, usually derived from crude oil or manufactured synthetically, that is then combined with additives to reduce wear, prevent corrosion and stop the oil from oxidizing. Conventional oil also includes specific detergents to keep your engine clean, as well as anti-foaming additives, explained manufacturer Pennzoil.

These additives are mixed into the oil to prolong the life of your engine. They're specifically formulated to clean away contaminants produced when gas burns to prevent buildup and deposits in the engine.

If additives like this weren't mixed in with your engine oil, contaminants could quickly build up in the oil and you'd be required to swap it out much more regularly. As it stands, you probably only need to replace your oil every 5,000 miles or so. 

Diesel oil, however, is a little different as it's engineered to work best in an engine that burns diesel fuel. The biggest differentiator is that it is much thicker than traditional oil, and it also contains different additives, as Machinery Lubrication explains:

The most prevalent are overbase detergent additives. This additive has several jobs, but the main ones are to neutralize acids and clean. Diesel engines create a great deal more soot and combustion byproducts. Through blow-by, these find their way into the crankcase, forcing the oil to deal with them.

Diesel engine oils also contain a compound that helps with wear, called zinc dialkyldithiophosphate, or ZDDP. This compound can cause havoc with the catalytic converter in a gas car, while diesel CCs are designed to deal with the compound.

The damage that ZDDP can cause to your gas car's catalytic converter is just one of the reasons why it's so important to ensure you're filling your car up with the right kind of oil.

The second big problem you could face stems back to the thickness of diesel oil. The higher viscosity of the liquid means that more friction can be generated between the oil and the engine components, causing it to heat up. This shortens the lifespan of the oil and can also increase wear on components as the thicker oil may not be able to flow where it's needed most.

Because of this, it's best to make sure you're using diesel engine-specific oil only in motors that run on diesel, and conventional oil in your gas powered car. Now, take this newfound knowledge and go forth for your first oil change! Good luck.