One problem related to water pump 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.
I believe the product to be defective because of the issue that I had faced with this vehicle 2 weeks back while driving in the freeway. Two weeks back while I was driving with my family (wife and 2 kids) the vehicle on 275 s freeway @ 70mph on 8th March 2015 1:00 am, the engine check light turned on and I noticed the engine heat indicator fluctuate like a fuel indicator. I tried to slow down, but by that time I lost the power of the vehicle , which made it really hard for me to steer the vehicle between the lanes and take it out of freeway to a shoulder, the brakes were not functioning either. It was one of my scariest ride I had in my life (you can imagine yourself, engine loosing power while driving in a freeway, I was with my entire family, and not having control on the vehicle), it put me and my family at such a big risk. Glad I was able to some how take the vehicle out of the freeway and used the parking brake to bring the vehicle to a stop at a freeway shoulder @ 8 mile road exit. The next day, I took the vehicle to victory Toyota of canton, a Toyota dealer for diagnosis. After thorough diagnosis from the dealer, he figured out the engine water pump failed, which lead to the engine getting overheated and engine got damaged, which needs to be replaced. They came back with the cost of 10,000 usd for fixing the vehicle. The vehicle has only 66,860 miles on the odometer.