One problem related to engine failure has been reported for the 2007 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2007 Toyota Sienna based on all problems reported for the 2007 Sienna.
Driving car in town for about 10 minutes. Stopped at friends house and noticed when I backed out a large oil puddle. Got out and looked under car to see undercarriage covered in oil from front of car to midway down car. Could not tell where it was coming from so I called tow truck to take to Toyota dealership. They found small hole in oil cooler line was spraying oil out. It was half empty of all its oil in that short amount of time. The dealership told me it was going to cost me $360. 00 to replace oil cooler lines. I was very lucky I had not driven very far or probably would have been catastrophic engine failure. After quick check on internet, this appears to be a common issue with oil supply lines in this and other model years. Also looks like there is a new all metal oil supply line and a warranty extension (ze2), neither of which I was made aware of by my dealership and was very difficult for me to find.