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.
Car Problem Reports
Toyota Highlander Sludge Buildup on Engine Due to Infrequent Oil Changes
Toyota Highlander Problem
Engine Affected: 3.0L V6
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.