I think we can all agree that the oil needs to be changed even though there is often some debate about when it needs to be changed. Have you ever thought about WHY you need to change your oil? There are several reasons, but the importance of changing your oil regularly has increased exponentially in the last decade or two because of advancement in engine design.
The main, and possibly most obvious, reason for engine oil is basic engine lubrication. The oil in your engine is distributed via a labyrinth of oil passages under pressure provided by the oil pump. In the old days, you simply changed your oil to keep your engine bearings happy. Modern engines, however, have many other things which are lubricated by or are dependent on oil pressure.
Timing chains and systems have changed greatly. An old dinosaur like a Chevy 350 would use a timing chain setup similar to this:
More modern engines, like this 2.2 Ecotec engine from a Saturn, have a timing system like this:
You can see the complexity of the later model (2001 in this case) timing set as compared to the older 350, but modern timing sets can be much more complicated than that! For example, the 4.7 Dodge engine users three separate timing chains, and four timing gears. Most of this complexity comes from the overhead cam designs used in modern engines. These modern setups use one or more nylon timing chain tensioners and guides which usually use hydraulic tensioners like this one:
Notice the small oil hole in the red circle. That’s where the pressurized oil enters the tensioner to keep the chain tight. If the chain gets too loose it can “jump time” and cause serious damage to your engine.
Another contributing factor necessitating regular oil changes would be oil jet like this one.
This little gem sprays engine oil on the timing chain to keep it lubricated. You can see how tiny these holes are. Just one little spec of dirt or other debris can clog these ports and prevent oil from lubricating the chain as it should. I suspect this chain failed because of a clogged oil jet.
In this picture, you can see where the chain has worn clean through this chain guide. There used to be a nylon pad below an L-shaped bracket and the chain simply cut through it like a chainsaw because it wasn’t lubricated properly.
Beyond all the things mentioned above, there are a myriad of Variable Valve Timing actuators (VTEC, VVTi, etc.) under today’s hoods. These are nearly all oil pressure actuated and are very sensitive to any contaminants that may be in the oil.
Next time you see that little sticker at the top of your windshield (you do have a sticker don’t you?), pay attention to the mileage and have your oil changed then! If you want to do it yourself you may be interested in this post. If you have any questions or comments, let me know in the comment section below. Hope this helps!