Using Heater

Cabin heat is provided by engine heat. If you start your car when the engine is cold and turn on the heat, the Prius decides that maybe you would like the cabin warmed up. To do this, it puts a priority on getting the engine warm enough to provide sufficient heat.

Normally, the Prius will stop the engine while you are coasting, running on electricity alone, or sitting at a traffic light. However, an engine that is off does not warm up. Therefore, if the heat is on, and it's cold out, the engine won't turn off when you are coasting, running on electricity alone, or sitting at a traffic light, until the engine has warmed up sufficiently to provide you cabin heat.

So, for the first 5 to 10 minutes, depending on how cold it is, your engine would be running continuously. Therefore, you will get significantly less MPGs.

This is easy to verify. When you are sitting at a traffic light on a cold morning with the heat on, you will notice that the engine is still running. Turn off the heat, and you will notice that the engine will immediatly stop. Turn the heat back on and you will notice that the engine turns on within a second or so.

Once you have been driving for a while, then the engine will be warm enough to continue to provide heat even when it is off. At that point, the car will return to it's normal gas saving operation.

 

Perhaps in a mild climate, you can forego the cabin heat. In a severe climate like mine, that's a no-no. At the very least, the cabin fogs up, and your fingers get cold, especially at -20 C and colder.

When you combine extreme cold and the need for cabin heat, fuel economy is much worse, especially in city driving. I speak from experience after putting up with last winter, with many -40 days.

So far this winter has been much milder, but a few things have helped reduce the fuel economy loss. In order of biggest improvement:

1. Fashioned a winter front. The lower grille is blocked off with a piece of paper machine rubberized felt. The two slits in the upper grille I cut a piece of 1/2 inch foam pipe insulation and shoved them in, as per Frank Hudon's suggestion.

This provides *much* more cabin heat, and even that one morning at -27 C, the ICE still shutdown at red lights, at least for a few minutes. Last winter, with no winter front, in temps much below -18 C, the ICE would run constantly.

The winter front surprised me. I wouldn't have thought a winter front would make any difference in city driving, unless you were driving something old fashioned with a solid-hub radiator fan. The Prius cooling system is obviously very efficient, even the minor airflow at city speeds provides a lot of cooling.

2. Pick a more "efficient" route. I find a constant 60-70 km/h provides maximum fuel economy. Within reason, driving an extra 10-15% may result in less fuel burned than a very inefficient route with many stop lights.

3. Mobil 1 0W-20 as a "winter" oil. So far, compared to the dealer 5W-30, Mobil 1 0W-20 has helped on the order of 10%. I would not recommend using a viscosity different from what the factory recommends. Please wait for my used oil analysis on this oil to see what - if any - effect there is on wear metals.

 

Also during the warm-up period electric resistance heat elements are utilized to assist the warm water heat which uses power from the battery requiring the ICE to run to keep up the charge.

 

Cabin heat in an automobile is energy that must be gleaned from some place. In this case two sources of heat are harvested. The gasoline engine generates excessive heat that must be dissipated. Coolant (mainly water) is circulated via a pump from the engine inners to the radiator. The hot coolant passing through the radiator (heat exchanger) is passed off to the outside air. When the cabin heater is operated, some of the hot coolant is diverted to a smaller radiator located in the air path of the cabin’s ventilation system. This radiator (heater core) transfers heat to the cabin. Because the hybrid design uses a smaller gasoline engine, it’s ability to heat the cabin under sever conditions is reduce. This model provides auxiliary heat generated by electrical resistance via a ceramic heater element. All of this requires electricity which is harvested from the battery. Replacing this battery energy consumes a minimal amount of fuel.

 

The electrical load due to the A/C compressor seems to have less impact than running the engine for heat. Even in Florida, I'm pretty certain you'll get significantly better MPG in the height of summer than winter.

Now, don't get me started on the fact that in Florida you get cars fitted with auxiliary electric cabin heaters and heated wing mirrors, but we don't in Britain...

 

Actualy since there is no physical load of an a/c compressor on the engine and that load is transfered over to the HV system you will notice no vehicle performance losses when a/c is running. On top of that, the a/c compressor is variable speed, so it turns and compresses based upon the needs of the cabin to attain and maintain a particular setpoint. It is a very efficient unit. In addition, I'm inclined to believe that my MPG loss due to a/c was negligible, maybe 2 mpg. My mpg loss due to winter is about 12 mpg. I'll take summer with the a/c on full any day over the winter.

 

We have a mild climate here but with a radiator blocker I can "afford" to keep my self warmer and still maintain engine temperatures and mpg. I keep the cabin temp down until the coolant temp is above 162F then turn the cabin temp up.

 

Same here! With help of CANVIEW!
Of because when I'm driving alone.