The heat recovery system, that the CCV is an integral part of, is designed primarily to reduce warm-up time/maintain the coolant temperature closer to normal after being parked. In cases where the drive is "normal", eg: 8 miles or more one way at near highway speeds, I doubt there would be any noticeable difference. In point-of-fact, cars delivered in a number of markets do not even have this system installed.
I just got a 2006 Prius that had no heat. Showed 34-36mpg on the screen! Changed thermostat first (didn't fix heat) and then mechanic ran code that said coolant control valve. His scanner also picked up a misfire cylinder 3....Keep in mind I had zero warning lights on the dash. Long story short the control valve brought back heat....and the spark plugs were really shot too! And my mpg immediately jumped to about 41-42mpg on the screen. So hard to say if it was plugs or the valve...or combo of both. But, wouldn't you think with bad CCV the computer would be tricked into thinking that the car is operating cold and run the gas motor for longer periods of time...and thereby ruining mpg? I am probably messing the mechanic lingo up (I'm really bad with cars) but I read something similar to that here before. That a bad CCV runs gas motor longer.
Not if you are driving the car at speeds above 20 MPH, the engine is running ALL the time. The ONLY part of the cooling system that controls engine temperature is the thermostat, it's more likely when replaced some residual air was trapped in the system that was purged when the CCV was replaced, returning the heater to normal operation.
I replaced thermostat/CCV at exact same time...And got air out of system same time. And changed spark plugs same time. For weeks MPG on display was 34-36 tops....After repair jumped to 41-42. Spark plugs were shot but didn't drive like they were shot. 161,000 miles.
