Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Diesel engines

I recently just heard that diesel engines run a bit harder than gasoline engines and they need extra lubricant. Also I heard that biodiesel is even more abrasive on the diesel engine. Does anyone else know of this?

Should I use a lubricant like Marvel Mystery Oil to help with that? Also is that okay to mix with biodiesel?


If your vehicle has a diesel engine, follow the recommendation in the owner’s manual as to the type of oil you should be using. There is no such thing as “extra” lubrication. The oil specified by the engine manufacturer will provide all the lubrication the engine needs for as long as you own it.

For information about biodiesel fuel, try

Stop basing your decisions on internet chatter and rumors. Diesel engines are DESIGNED to deal with the loads imposed on them. Just use oil rated for diesel engines, whatever your engine manufacturer recommends IN THE OWNERS MANUAL. You CAN BE SURE Marvel Mystery Oil is NOT listed. Marvel is simply a light mineral oil with some red dye and and a little Oil Of Wintergreen mixed in…Properly filtered, there is nothing “abrasive” about biodiesel…A little kerosene (10%) might aid winter starting and prevent geling. Ask your suppier or the legions of internet experts…

I recently just heard that diesel engines run a bit harder than gasoline engines and they need extra lubricant.

No, they don’t need extra lubrication, but they often need oil that meets different specifications than gasoline engines. Generally the oil needs to handle more soot in the oil so it needs extra detergent in the formula.

I heard that biodiesel is even more abrasive

No, but it can cause problems on diesels not designed for it. On some diesels it may not be compatible with some of the parts in the fuel system and various failures may result.

Both issues are easily handled by doing one thing:

Read the owner’s manual and follow the instructions there.

Because diesel acts like a lubricant, it’s actually generally a lot easier on moving parts than gasoline. Many parts rely on the diesel to lubricate them, most importantly the injector pump, which is a very important and expensive part.

Commercially-produced bio-diesel is generally fine with most diesel engines, but that’s not to be confused with vegetable oil. The terms are often used interchangeably by many, but they are not the same thing. Bio-diesel is usually produced in large-scale operations and is purpose made as a motor fuel. Though it comes from biological sources, most commonly soy-beans, its properties are generally pretty similar to diesel. Veggie oil (waste or otherwise) is exactly what it sounds like-- it’s vegetable oil and it’s designed for cooking, but can be used as a fuel. The major problem with veggie oil is that it’s slightly corrosive and it will eat away at rubber fuel system components on older cars. It also has different lubricity characteristics from petroleum-derived diesel and on some cars the life of the injector pump can be shortened somewhat. Adding a supplemental lubricant with veggie oil might lengthen the life of the injector pump, but probably not by any really measurable amount and certainly not enough to justify the cost of buying the stuff, and it would do nothing for the rubber corrosion problems.

A small amount of biodiesel such as 2% added to your regular fuel enhances the lubrication qualities of commercially available diesel fuel that are needed for your injection pump and injectors which are not lubricated by the engine oil. The biodiesel is normally not needed but will serve as a guarantee that the lubrication qualities lost by removal of sulfur from petroleum diesel for air pollution requirements are not lost. Injection pump lubrication additives are commercially added but are not guaranteed to preclude undue injection pump wear and you can be sure that there will be many truckers who will loudly object if their diesel injection pumps wear out prematurely if the lubrication additive is forgotten or used too sparingly. You will likely not find this topic addressed in your owner’s manual. A little searching on the Internet would be good to do.

In general, diesel engines are used for large vehicles that haul a lot of weight. So, generally, they are asked to do a lot of work compared to the average car and commercial diesels spend a lot if time sitting idleing. However, a modern diesel car doesn’t necessarily work any harder than a modern gasoline car.

Diesel fuel used to be a biproduct of gasoline production. It was so unrefined back then that it helped lubricate the diesel engine. However, today’s low sulfur and ultra low sulfur diesel are much more refined. However, testing of biodiesel shows that it lubricates better than normal low sulfur and ultra low sulfur diesel. So if you really feel you need extra lubrication in your diesel engine, buy biodiesel.

One last point. Your diesel engine uses motor oil for lubrication. If your fuel also lubricates your engine, that is a bonus that may allow you to extend your oil change interval. However, if you change your oil as often as you should, you should not need to worry about this issue.