Most oil advertising, when you get past the claims about how they are much better than the competition, make claims about engines being prone to the dangers of engine sludge.
What is this mysterious engine oil sludge?
Oil sludge is what forms when you don't change your oil often enough. Oil functions in several important ways. It obviously provides lubrication and protection against the frictional damage of two metal surfaces rubbing against each other. Oil also contains additives like detergents, anti-oxidents, dispersants and anti-foaming agents, each of which performs an essential function to protect your engine.
Detergents clean undesirable dirt and byproducts from the metal engine surfaces, protecting and extending their life. Anti-oxidants protect the oil's life by stopping dangerous chemical reactions (oxidation reactions) that can break an oil down and shorten its life. Dispersants grab hold of particles like dirt and dust and keep them trapped in the oil film and away from metal surfaces that they could otherwise damage. Anti-acid additives (not yet named) neutralize harmful acids that form in the engine environment to protect these same metal surfaces. And anti-foams keep the oil lubricating film strong and intact by resisting air that threatens to get worked into the oil and destroy its lubricating ability.
So as you can see, the oil has a lot of responsibility going on. And we haven't even mentioned that oil is supposed to function in cooling the engine by moving heat out of key metal parts. That's important, too.
Oil sludge forms when the oil isn't changed often enough. As the oil change interval extends further past the point that all those protective additives have been used up, the oil fills with contaminants and oxidation materials (which would be cleaned out of the engine if the oil had been changed). Now it's not best able to resist the oxidative breakdown that can occur as the spent oil is continually exposed to more heat and pressure within the engine environment. Soon, the oil reacts and polymerizes into a sticky gel that can either sit in the oil crankcase or coat whatever metal surfaces it gets carried to.
Because it's a good insulator, it can cause your engine to retain heat, leading to stress and shorter life for your cooling system. And since oil sludge is actually part of the oil itself, when you get sludge development it means you have less actual oil lubricating your engine.
What To Do?
You can prevent the formation of oil sludge by making sure that you change your oil when it is recommended. That's the single best thing you can do for your vehicle. If you do have engine sludge (if your mechanic points it out or if you're skilled enough to look for yourself, check out your valve covers), you can use a quality engine flush like Bell Performance Engine Flush to clean the sludge out. And it won't cost you $40 or $50 like it might at an oil change place.