Posted 08 August 2003 - 10:49 PM
I use Mobil 5W-30 in both of my cars, the Lexus of course, and a '94 Camaro Z28. Neither burns any oil, and neither has any leaks.
In most cases I have found, and certainly with some customer cars, that oil burning is the result of piston rings which get sticky from infrequent oil changes. What can correct that condition, over time, is regular oil changes with a quality oil. The fresh oil will tend to clean varnish and deposits out of the ring grooves and allow the rings to conform better to the cylinder walls. My advice would be to shorten up the drain interval - maybe 2000 miles or so - for a few changes and then monitor the oil consumption. In most cases the engine will begin to burn less oil. Also be sure the crankcase breather (PCV valve) is in good condition, as when it plugs the internal crankcase pressure goes up and that can push oil past the rings.
In some cases I have flushed very dirty engines with good conventional oil, on very short changes, like 100 miles or so, and then gradually increased the interval as the engine cleaned itself internally.
At the end of it all, if the engine does continue to burn oil, but doesn't foul any one sparkplug (all cylinders are burning a bit) and the catalytic convertors continue to function efficiently, then simply add a bit of oil between changes and don't worry about it. If one cylinder seems to burn the oil, that would indicate a mechanical problem, if all do it evenly, then it is just normal wear.