The first column I wrote for The River Reporter three years ago was on synthetic oils. It covered the basics about oil changes and the many advantages synthetics have over regular oils. Now, three years later, has anything changed? Several things.

Now every manufacturer offers synthetic oil and existing brands have been reformulated and improved. There are more synthetic blends around, too. The blends are supposed to bridge the gap between true synthetics and regular oils in terms of price and performance.

A major advantage of synthetics is their ability to remain stable at high temperatures without breaking down or oxidizing. Petroleum-based oils will boil away at high temperatures. By-products of oxidation include tar, sludge and thickening.

While petroleum-based oils boil, a good synthetic will lose only about 4 percent of its weight. At higher temperatures, 475 degrees and above, conventional oils will volatize completely. Synthetics, originally developed for use in jet engines, will continue to lubricate at 700 degrees.

Eventually, all the oil in the crankcase will oxidize and breakdown which is the reason for the recommended 3000-mile oil change interval for regular oil. The oil gets saturated with contaminants that are byproducts of the oil's own decay and not contaminants produced by combustion. Synthetics don't need to be changed as often because they don't decay like regular oils.

Several manufacturers use synthetic oils. Porsche uses Mobil 1, with 15,000-mile oil change intervals. Corvettes use synthetic oil exclusively. I've been using synthetics for years-with 10,000-mile oil change intervals.

Besides its resistance to viscosity loss at high temperatures, synthetics also have much stronger film strength, which is the amount of pressure needed to force out a film of oil between two flat pieces of metal. A good petroleum-based oil measures at 500 lbs while most synthetics hit the 3000 lb. level. This is important-because of this there is much less blow-by past the rings and thus less oil contamination.

Another benefit of synthetics is their ability to lower oil temperature in the crankcase. Oil not only lubricates but also serves as a coolant medium, drawing heat away from the engine's reciprocating parts. As temperatures rise, petroleum-based oils have a tendency to bead on the metal surface while synthetics will wet the entire surface, showing affinity for the hot metal rather than itself. The lower oil temperature extends engine and oil life.

Besides these benefits, synthetics offer less resistance so the engine produces more power, usually in the 2-3 percent range. Because there is less internal friction, an engine will use less gas, too-in the 3-4 percent range. I got a 1.5 mpg mileage increase on my 1998 Neon and highway mpg went from 30 to 31.5 when I switched to Mobil 1. It doesn't sound like much, but a 5 percent increase can add up.

Mobil has been advertising their newly-formulated synthetics as being even better than before. They've tested a new engine from the very start and at 300,000 miles the engine showed no measurable internal wear. At 1,000,000 miles there was wear, but the engine was still in good condition.

Most people are still leery when it comes to long oil change intervals. If your car is still under warranty, you should go beyond the manufacturer's guidelines unless the manual says you can if you use a synthetic.

All I can do is pass on my experience. Our AWD Caravan now has 220,000 miles and I've been changing the oil every 10-12,000 miles (filter every 5,000) and the engine runs like a top.

As for the blends, they cost about half the price of a synthetic and my feeling is, what's the point? They don't state what percentage their synthetic content is, either. If you're going to use a synthetic, you might as well use the good stuff.

[Peter C. Sessler is the author of 25 books on cars, published by Motorbooks International, Tab Books, Smithmark Publishers, and HP Books. Some of his titles include "Ford Pickup Red Book," "Muscle Car Greats," and "Car Collector's Handbook." Publication is pending on his latest book, "Model Car Handbook," to be published by Scale Sports.]