I have been noticing that as it has gotten a little colder out and my heater has been running, that my mileage has gone down. I have now had the car for about 7 weeks and driven a little over 3,000 miles. My mileage has averaged somewhere around 39 (just over on the display and just under when calculated). With the heat on it seems to be closer to 38, not a big difference but a little confusing. I am used to a car whose air conditioner lowers fuel economy, not the heat. On the TCH, the air conditioner doesn't seem to effect the mileage, just the heat.

Any ideas what may be causing this???

 

Fisher. I actually find that the A/C has a big effect on efficiency, about 3 - 4 mpg according to my very unscientific observations.

I know what you mean about heat, but it may make sense in a hybrid. Normally the engine stays on all the time, but that's not the case in a hybrid. The engine will come on to get the TCH to operating temperature. Perhaps the ICE needs to run longer on start-up to reach the temperature and it's also possible the engine is cooling down requiring it to again start up because of temp.

I do have to say that for the few minutes at a time the ICE might be off it doesn't seem likely that it would cool down enough to have a big effect on temperature.

 

I noticed that around 50-60 F there is huge difference how long the engine takes to warm up. At 60-70 F it takes about 2-3 min. for the engine to warm up and then shutdown if not needed. Bellow 50F it may take as much as 10 min. It will probably get even worse when temperatures drop way bellow freezing but we didn't have that here yet.

 

Yesterday morning it was 34 degrees, rolled out of garage on batt then engine starts closed garage door drove 500ft to gate opened gate(homelink) drove thru gate stoped closed gate(homelink) and engine temp was 1/4 in below where it normally runs. This car warms up faster than anything I have ever seen, I suspect a large electric coolant heater. SK

 

It's not only using your heater: it's the effects that cold weather has on ALL cars. Read on:

Getting low MPG in cold weather is not a problem with hybrid technology, per se. If it was, there would be ZERO drivers achieving EPA numbers in the winter months, and that is not the case.

There are many reasons for cars not achieving max MPG in the colder months...

Car engines must warm up to a certain internal operating temperature before they most efficiently use the fuel. Winter months and colder temps make that transition from cold start to most efficient take a little longer.

Also: new cars go through what is called a "break-in period" where the metal engine parts are still grinding against each other more rigidly, creating more friction, which also reduces efficiency. Over time, the "extra metal" shaves off and gets lubricated better (expecially if you use Synthetic Oil) and the friction is reduced, which affect MPG numbers. A lot of us with a TCH are still in the break-in period.

The hybrid systems are also tuned to work best with a warmed-up engine. So you will be using electric assist less often until your vehicle warms up.

Winter formula fuels used in most states hold less energy and this also hurts MPG.

Generally speaking, colder weather in many areas means "rain, snow, or slush or ice" on the roads - these things add additional resistance which the tires must push out of the way to contact the road, so they hurt MPG in that way.

Tire pressures also are lowered by the cold weather too. Most people fail to properly inflate their tires all year, but ESPECIALLY in the winter when it is cold and you might have dirty tires and you just don't want to deal with spending time in the cold airing up a dirty tire. Low tire inflation adds quite a bit of rolling resistance, which forces the engine to work harder to "push" the car forward, thus using more fuel.

Additional idling uses more fuel and hurts overall MPG, and many people in cold climes by habit or necessity are warming their cars up in the morning. That is good practice to stay warm, but BAD for MPG numbers. While idling in your garage or driveway or carport, it is getting 0 miles to the gallon !!

People who use the defroster in a Hybrid are many times using the A/C compressor to help reduce the humidity in the car and clear the fog. That is a MPG killer too. The compressor can be turned off, but usually by default it comes on.

Personally, I am looking into some kind of engine block or oil heater system to help combat the cold. My current tank, with mornings being in the upper 50s and low 60s for the past week has dropped to 35.2 after 50 miles.

See this science page for more explanation:

http://tinyurl.com/3s7lo

 

FisherJ:

Are you aware that there's an electric heater built into the TCH? It can operate to provide the passenger compartment with heat until the internal combustion engine (ICE) reaches its normal operating temperature range, provided the ECO mode is switched "off." Then the ICE takes over. Of course, this electric heater depletes the 12-volt battery, which needs to be recharged by the ICE, thus degrading fuel economy overall. If you switch ECO mode to "on," this electric heater is disabled, and you have to wait for the ICE to warm up before hot air is provided. [ECO mode also reduces NiMH battery power usage by the air conditioning compressor when switched "on."] Try switching ECO mode "on," and see if this improves your mpg. You'll have to wait longer for heat, though!

Stan

Notes:
(i) This electric heater heats the air directly, it does NOT pre-heat the ICE coolant.
(ii) So far as I can tell, the TCH does NOT incorporate a thermos flask, like the Prius, to keep the engine coolant hot overnight. This conclusion is based on examination of the inside of the engine compartment as well as a perusal of the Service Manuals.