Dear Tom and Ray:

I am the proud owner of a '67 VW Bug. It is a great little car, but leaks about a quart of oil every 1,000 miles. Since it only holds three quarts, and since I have put in three quarts by the time I reach 3,000 miles, is it necessary to change the oil every 3,000 miles?
Steve

TOM: Changing the oil on a '67 VW Bug. Isn't that a little like worrying about the curtains on the Titanic, Steve?

RAY: Actually, the answer is yes, you should change the oil regularly. There are two main reasons for changing the oil. One is to replace the old, broken down oil with new, more effective lubricant. But the other--just as important--reason is to clean the junk out of the engine.

TOM: The motor oil picks up and suspends small contaminants (i.e. dirt) that get past the oil filter. So when you drain out the oil, you're also draining out a bunch of the dirt the engine produced in the last three thousand miles, along with whatever small pieces of the engine may have also fallen off during that time.

RAY: If you never drain the oil, that dirt is just going to stay in the engine and turn to sludge.

TOM: But more importantly, if you don't change the oil in this car, you'll never change the screen. VW Bugs, as you probably know, Steve, don't have oil filters. Instead, they have a screen that is supposed to be cleaned out with each oil change. If you never clean it out, it'll eventually get plugged up with crud, and your engine will melt.

RAY: And when it melts, you may notice some, small, incremental decrease in performance.... especially on hills.

TOM: So if you really do like this car, Steve---and you say you do---go ahead and change the oil every 3,000-5,000 miles. And better yet, get the leak fixed, too.