Two problems related to oil pump have been reported for the 1999 Toyota Sienna. The most recently reported issues are listed below.
Engine oil gelled/became sludged in July 2002, oil pump failed in November 2003.
Engine of 1999 Toyota Sienna (van) had sludged engine oil in July 2002, dealer rebuilt engine. In November 2003, oil pump failed on same vehicle. Dealer contends the failure of the oil pump is not related to the engine oil gelling/becoming sludge. Since engine was rebuilt, owner has changed oil every 3,000 miles and has receipts to prove it.