Q I just purchased a 2003 Buick Park Avenue with 203,000 miles. It's in good shape, and I foresee driving it for the next decade with good maintenance.

I have been told that I can change to a synthetic oil, and using special filters I would never have to change the oil again, unless it became contaminated and the filter didn't seem to be taking care of it. I was told this is because synthetic oil will never break down at normal or even high operating temperatures. So I could just change the filter every 3,000 miles or three months and replace the oil lost in the filter.

My mechanic says that even with synthetic oil, I should change it every 5,000 to 6,000 miles. He says he's seen cars where the owners changed only the filter, and inevitably the engines are coated with sludge inside. What do you recommend I do?

A Listen to your mechanic. Change the engine oil and filter -- regardless of the type of oil you choose to use -- every 4,000 to 5,000 miles. With your estimated 7,000 to 10,000 miles per year, that would be twice a year at most. Even at $50 per synthetic oil change, why would you not change oil and filter?

Every automaker's recommended maintenance program includes regular oil and filter changes. Every automotive warranty requires following the carmaker's maintenance schedule. And the bottom line, of course, is that it's your name on the title and registration.

Yes, synthetic oils are better at maintaining viscosity than petroleum oils, but they contain the same additives to protect against corrosion, foaming, wear, etc., including additives that work as dispersants to keep contaminants suspended in the oil. Additives are consumable, meaning they're used up over the service life of the lubricant. Motor vehicle engines use full-flow oil filters that filter every drop of oil before it is pumped into the engine. These filters trap particles down to 10 to 15 microns. Any finer filtration could restrict oil flow in cold conditions. That's why you need to change the oil and filter.

No matter the type of lubricant -- petroleum or synthetic -- soluble contaminants like combustion acids, water and fuel can remain in the oil until it is changed. A bypass filtration system that pumps some of the oil through a much finer filter might justify longer intervals but wouldn't eliminate the need to change oil.

Modern automotive engines and lubricants are far better than even those of 10 to 20 years ago. But they still require regular maintenance -- which is your responsibility. You make the decision.

Q I own a 2003 four-cylinder Camry with 110,000 miles. After the car is parked overnight and then started, smoke comes out of the tailpipe for about two seconds. The car does not burn oil between oil changes, nor does it emit smoke at any other time. What could cause this smoke?

A What color is the smoke? White smoke could indicate coolant leaking into the cylinders and vaporizing with the heat of combustion as the engine starts. A cooling system pressure test and/or testing for exhaust hydrocarbons in the coolant might pinpoint a leaking cylinder head or intake manifold gasket. White smoke can also be normal moisture accumulation in the exhaust system vaporizing at start-up.

If the smoke is blue, it's a tiny amount of oil that has drained past the valve seals into the combustion chamber overnight and burned when the engine is started. At 110,000 miles, this would not be abnormal and doesn't indicate a problem that needs repair.