A Slippery Subject

Just because you may never put 3,000 miles on your garage queen engine doesn't mean that you shouldn't change the oil. Water can combine with sulfur and fuel contaminants to create acids that can eat bearings. The pits in these bearings were created by acids.

For example, Farner says that for every pound of fuel burned in an engine, the combustion process also creates a pound of water. Some of this water will eventually end up in the oil pan. If the engine rarely sees sump temperatures that exceed 212 degrees F (water's boiling point), the water quickly mixes with another combustion byproduct--sulfur--to create acids that can eventually eat bearings if the oil is not drained.

Another reason to perhaps shorten drain intervals for performance engines is that oil is an important component of ring seal. If engine oil is contaminated with water, the water evaporates almost immediately around the rings, reducing ring seal and horsepower. Several years ago, we witnessed this firsthand at the U.S. Nationals when John Lingenfelter's small-block-Chevy-powered Pro Stock truck suffered an internal water leak. Once the water mixed with the engine oil, the 9,000-rpm engine lost double-digit power, which cost him the race.

The ultimate seal with piston rings is assisted with engine oil. The highest friction loss in an engine is found between the rings and the cylinder wall. Quaker State's research indicates that a too-thin oil can actually vaporize at the top ring, sacrificing ring seal.

Fuel is another contaminant that is often found in engine oil. Fuel can enter the oil from several places, most commonly as blowby past the rings. Even though we think of fuel as easily evaporated, according to Farner only the light ends of fuel evaporate at room temperatures. The heavier ends require temperatures as high as 450 degrees F to fully evaporate, which means that even at 300-degree oil temperatures, there can still be residual fuel that tends to reduce your oil's effective performance.

All of these are excellent reasons normal drain intervals are a good idea, even if you decide to step up to the more expensive synthetic oils. There are also synthetic blends offered by most major oil companies that are a composite mix of both synthetic and petroleum-based oils and are less expensive, but also reduce the oil's overall potential performance.

Track days on road courses are becoming increasingly popular with the Pro Touring crowd. Even a couple of laps of wide-open throttle use will rocket oil temperatures far above 300 degrees F if the engine is not equipped with an oil cooler.

Thinner Is Better?
Besides the inherent high-pressure lubrication advantages in areas like the cam and lifter interface and piston rings to the cylinder wall that synthetics offer, there has been a move in the last few years to create lighter viscosity oils that can still deliver protection and temperature stability with thinner oils that are easier to pump. It's a generally accepted fact that thick oil tends to create higher oil pressures. The thicker or more viscous the fluid, the more power is required to push the lubricant throughout the engine.