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Can You Put Regular Motor Oil in a Diesel Engine?

It happened. You accidentally put gas motor oil into a diesel engine. It’s an honest mistake; people do it all the time. Maybe you just dumped a little 10W-30 into the crankcase, or maybe a rookie mechanic did it at your shop. Is it going to blow up the motor? Or is everything fine? Diesel oil and gas oil have different properties, so here’s what happens if you put regular motor oil in a diesel vehicle.

The answer is: it depends. For example, some diesel engines can use 5W-30 oil, which is a common gasoline engine oil. Using synthetic is a safer bet. But some diesel engines (specifically newer ones) require different oil that has special additives for emissions control and engine cleaning.

Can You Use Gas Engine Oil in a Diesel?

Diesel engines (especially in pickup trucks) take a ton of oil. The 6.7 Cummins diesel takes 12 quarts, and the old 7.3 Powerstroke takes 13. It may be tempting to use cheaper oil meant for gasoline engines. So, can you use gas motor oil in a diesel engine? Well, it depends. In short, it’s usually best to use diesel oil in diesel engines. But it matters more in some engines than it does in others.

Why Can’t Some Diesels Use Regular Motor Oil?

Diesel engines that aren’t designed to use standard motor oil can’t for a number of reasons, and doing so can cause damage to the engine.



Here are some of the reasons why you can’t run regular gasoline engine oil in certain diesels. Small “EuroDiesel” engines used in cars and compact trucks often fall into this category.

-Detergents

For example, everyone knows that diesel engines run a lot dirtier than gasoline engines. This is because diesel fuel is a lower-quality and less refined fuel, and contains a number of impurities. Diesel motor oil contains essential detergents that clean carbon and other gunk out of the engine. Detergents are especially important on modern light-duty diesels, as excess gunk can foul up sensitive (and expensive) parts.

-Additives

Detergents aren’t the only additives in modern diesel oil. In some areas, it’s helpful to run diesel oil with cold-weather additives to encourage lubrication on sub-zero days. Remember, the viscosity of oil declines when it’s cold, and so do its lubricating qualities.

-Emissions

Sometimes, diesel oil contains additives to help reduce emissions. These additives are less important to some individuals in the diesel truck community, which is quite alright.

Can You Use Diesel Motor Oil in a Gas Engine?

Using diesel motor oil in a gasoline engine is typically fine provided it meets the specifications of the motor. Make sure the viscosity is correct; you don’t want to put heavy oil in a car designed to use an ultra-light oil. Some brands sell dual-purpose oil for diesel and gasoline engines.

Still Not Sure? Where to Find Out

If you’re concerned about using gasoline engine oil in a diesel engine, just check the forums to see if your engine can use standard motor oil. The owner’s manual may also provide some direction. Chances are it’ll be fine for a while. But if your diesel can’t use oil meant for gas engines, it’s best to drain and replace the oil as soon as possible.