Gas Mileage Deterioration

welcome!

winter temps can reduce mpg' up to 20% or more. so cooler mornings could be part of it.

lack of the shield reduces aerodynamics, another factor.

check your tyres pressure.

inverter coolant keeps the inverter cool. there is a reservoir under the hood on the firewall. check it when checking all your fluids when gassing up.

make sure your air and cabin filters are clean, and the oil level is between the high and low marks.

all the best!

 

A Gen2 Prius (2004-2009) usually averages 46 MPG, not 50. It will get somewhat better MPG in mild weather and get less in cold weather. You should check the air pressure in your tires as tire PSI will drop at colder temperatures (This is a law of physics) and that will reduce your MPG as you noted. I always run my Prius tires at 42 psi in the front and 40 psi in the rear to maximize MPG, but it still drops in cold weather.

As for "coolant" there are two independent coolant loops in your Prius. One cools the gasoline engine (ICE - Internal Combustion Engine) and the other cools the Power electronics unit that manages the electrical power that goes to/from the motor generators (there are two MGs). The power electronics perform several functions, one of which is to generate high voltage AC power from the 200+ V High Voltage (Traction) battery, This process is called "Inversion" so we tend to call the unit an Inverter.

JeffD

 

like your avatar.

 

As already mentioned, there is nothing wrong with 45 MPG in a Gen2 Prius. 50 MPG is for Gen3, but many folks drive too fast to get that.

Here are two relevant posts:
Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat
Why Mileage Gets Worse in the Winter | PriusChat

 

The short hops are MPG killers. The engine has to run to get up to operating temp and to heat the cat. The colder the outside temp the longer it takes. Blocking the grill will keep more of the generated heat in the engine compartment. Search for "grill blocking" and you'll find a number of approaches.

There have been winters where a 35 mile mostly highway commute won't keep the engine warm and waiting for a traffic light was long enough for the coolant temp to drop enough to cause the engine to fire up.

Without knowing the particulars of your route there's no way to guess what you could expect. Just pumping in a "little extra" gas to round up a purchase or the bladder stiffening to take less to "fill up" will cause wild swings when measuring fuel economy tank to tank.

 

50+ mpg is great but those who get it only show what is possible with their individual cars, not what you should expect from yours. Fuelly.com doesn't have an easy way to see what 2009 Prii still being reported are getting but the overall average for 2009 is 43.5. All the Gen II are in the 43-44 mpg range. Keep in mind that with those 50+ people in the mix there have to be enough under 43 to get the average down to where it is. It's great to want to improve but also be happy with your "above average" car. Enjoy it and don't fret too much about it.

 

For the first minute the car is on (or longer if it's colder), the car operates in open-loop mode, meaning that it's not really using the sensors to determine fuel mixing and timing, and so runs the engine very rich and with conservative (fuel-inefficient) timing (Stage 1 Warm-Up). Once the o2 sensor and radiator water temp warm up enough to operate correctly, the Prius will get much better fuel economy(Stages 2-4). If you have to immediately go hard on the gas after starting, you'll likely get better fuel economy by starting the car and waiting a minute before driving off. See this for a full explanation on the Prius warm-up stages: http://techno-fandom.org/~hobbit/cars/five-stages.txt

Yes, all cars get worse fuel economy in the winter due to needing longer to warm the engine up to ideal operating temp, and that the air is actually denser, resulting in more aero drag on the highway.

This one is definitely affecting your fuel economy. I had the exact same happen to me - it tore off on me on the interstate. I immediately started seeing about 5mpg less on the highway. After I fixed it (with lots of epoxy and some plastic sheets), fuel economy was restored.

 

The shield under the radiator is not to force air its to keep road damage like rocks and debris from damaging the very expensive AC Condenser which sits in front of the radiator. Punctured condenser no AC and possible damage to the AC compressor. Its very important you have that shield installed. The G2 is very low to the ground and it will pick up alot of debris.