TORRANCE, Calif. -
Close to 650,000 Toyota Prius models across the world will need to have their water pump repaired to fix a coolant issue, according to various news reports.
Toyota Motor Sales USA spokesperson John Hanson told Auto Remarketing on Tuesday that approximately 378,000 Prius models are impacted in the U.S. 

The model years of the affected vehicles range from 2004 to 2007.  
Toyota said it is addressing a possible issue in the water pump that that may lead to the coolant overheating.
If that happens, the power output of the vehicle could be diminished.
Hanson stressed that this action is neither a recall nor a safety issue, but what is what is referred to as a “limited service campaign.”  He explained that the water pump is vital in cooling the hybrid components.
“The water pump is part of a system designed to cool the hybrid powertrain components and is separate from the engine cooling system,” Hanson noted. “A fault in the water pump can cause air bubbles to build up and disrupt the flow of coolant, which can lead to overheating.”
The check-engine light could light up if the hybrid components heat up. Eventually, the vehicle could go into “fail-safe model” should the hybrid components get overheated, officials explained.
This is designed to keep the components from being ruined. Toyota is asking owners of affected vehicles to bring in their vehicles to be fixed.
“This program basically extends the warranty period to allow them to do that,” Hanson shared.
 Starting early this month, the automaker is sending notifications via first-class mail.
 Owners can have their water pump replaced for free provided they request an appointment before Nov. 30, 2013.