Sludge can build up in the engine because Toyota did not recommend frequent enough oil changes. Lexus will sometimes offer a discount on cleaning the engine if necessary. Owners who changed their oil every 3,000 miles did not experience these problems. This sludge build up can lead to excessive oil consumption.Google+
Car Problem Reports
Toyota Highlander Sludge Buildup on Engine Due to Infrequent Oil Changes
Toyota Highlander Problem
Engine Affected: 3.0L V6
Average Mileage: 56,156 mi (42,312 mi - 70,000 mi)
Visitor, 2001 Toyota Highlander, 3.0L V6, 70,000 mi
Suddenly started using one quart of oil per 100 miles but only on highway 60 mph or more. Around town used no oil. Regular oil changes were always done.
Visitor, 2002 Toyota Highlander, 3.0L V6, 42,312 mi
3 quarts of oil in 500 miles, so much for toyota reliability. I sould have bought another Ford.