I have had my prius for about 5 months now ... the pump noises from under the hood when i shut down the car have become louder as the colder weather has moved in. It almost sounds like it is grinding or something. Also i have noticed that my milage has dropped significantly ~50 to ~35ish .... are these characteristics normal? thanks.
The fuel economy drop is to be expected. Any car's FE drops in cold weather. The effect is exaggerated somewhat in the Prius because of its unique warmup sequence. Some of us use an engine block heater and/or block the front grille to improve winter FE. There are several threads on each; a good search should tell you all you need to know. The noise you're hearing may be the coolant heat storage pump. If your car has less than 60K miles, it may qualify for replacement under this TSB.
