Why is the internal combustion engine running?

The ICE needs to keep itself and the catalytic converter warm to limit pollutants.

If you are traveling at more than 42mph (67kmph) the ICE will always run, to protect the electric motors from overspeed.

 

The weather is colder, now. The ICE needs to run more often to keep the engine/cat at a nice toasty temp. This is normal operation for a Prius in BC. You won't see decent fuel economy numbers until June . If you really want some better numbers, get an engine block heater (ebh) or the thermistor hack.

 

Not precisely true. The pistons in the ICE must be rotating over 42 MPH but it does not necessarily use fuel or spark.

AND, there is no 'ICE running' indicator so you can be moving on electric, showing 99.9 MPG but the ICE can still be idling on a small amount of fuel.

 

There are a lot of factors affecting mileage. As the other posters have noted, mileage goes down in the winter. That said, 35 mpg is really low. My winter mileage drops from 56 mpg to around 46 mpg. Obviously shorter trips will make it worse.

Tell us what your typical trip is like.

Tom

 

I'm guessing since you are in a cold region of the world, that you have the heating on a lot. I've noticed since it started to get cold here and thus I have the heating on, that the ICE runs a LOT more. After having the car on for, say, 15 minutes, if the ICE is still idling, try pulling over and completely turning off the heat and blower, and see what happens. If the ICE goes off, it was just on for heat.

Even 36mpg is still really good - in my experience even at those 'low' numbers you are practically guaranteed that fuel economy. Can anyone say the same for a Corolla etc. ?

 

We are just about 35 miles north of you and gased up today.
41.98mpg (Imp)/34.95mpg(US). Driving includes several trips over the Malahat and we use our heater generously with gas at $0.889 (today). Suggest you ask some of your friends driving the gas guzzlers what their mpg is during the winter up here and think you will be pleasently surprised-----I was ever since owning a 2005 and now the '08.
Enjoy
Gary

 

I don't think a lot of the responders read the OP very carefully.

What he describes is a mystery.

 

Nothing kills the fuel economy more then heating the cabin. Try setting the Auto A/C to 65 or off. Also as it gets colder your tire pressure will decrease, this is a good time to check your tire pressure.

 

Someone pumped your tyres up.

 

I can understand the frustration with varying MPG. The little unknown secret of the Pruis is that on short trips of 10 minutes or less, a driver will never obtain the high MPG that is expected. All of the respondents are correct; short drives, outside air temp., wind, and tire pressure make a BIG difference and each other above can change on a daily basis. I use to get frustrated thinking it was the quality of gas but it has also has to do with factors that I can't control. Just enjoy the car and accept was MPG or KPG you achieve. It is still a good value.

 

OK, it seems you are getting too low mileage. Even I get 5.3 l/100 km right now, and I drive short trips and it's not warm (just above or at freezing).

1. Make sure your tires are inflated properly. Putting more in them than the door post indicates is a good idea. I use 40 PSI front, 38 PSI rear. Have you changed the tires? Most replacements will cause you to get poorer mileage. I use Nokian WR true all-season tires. They give as good or better mileage than the stock tires. Available at Kal Tire.

2. The engine will run for 30-45 sec. after you turn on the car to warm up the cat. It will do this whether you have just driven the car or not. It's a cycle it runs through whenever you turn on the car. I have never noticed the car running to "warm up the cat" at any other time. It's a minor cause of engine running, as the cat warms up so quickly.

3. I use A/C Auto. The switch to control this is on the steering wheel. If you have this on when you start the car, and the temp in the car is below the set temp the engine will run. It will run for no good reason. Prius will not warm up unless you drive it. It WILL warm up within a few blocks of driving. So, turn off the A/C whenever you come to a stop. The engine will usually stop within 10 sec of stopping once the coolant is above about 50C. When you go turn it back on. This will maximize your winter fuel economy. Once the coolant is over about 62C the engine will stop even with A/C on and demanding heat. So you only have to do this when the car is "cold".

4. I'm sure a block heater will help, but I don't use mine at all. I can't predict when I'll be driving. So if I can get in the low 5s l/100km in the winter it should be easy for you. Note that I saw low 6s in the dead of last winter, when it was in the -20s outside.

5. Because the Prius engine is so efficient, it struggles to keep the car warm. I'd recommend blocking the grills. Use ethafoam pipe insulation. I use the 3/4" for the top grill and 1 1/2" for the bottom grill, with two zip ties each for holding it in. Search the site for more info. This is safe until the ambient temp gets above 20C.

Let us know if the above ideas help. I doubt there is anything wrong with your car, but doing the above will tell. If it helps then your car is "normal".

 

What he describes is, in fact, completely normal. Read the
five stages document. If you never crested 34 MPH on your trip,
and it wasn't long enough to sufficiently heat the ICE to the point
where you could stop and do the "idle dance", you never got out of 3a.
.
No mystery, just annoying operational quirks.
.
_H*

 

Are you past the 5,000-or-so mile marker yet? Thats when the Prius' parts get "broken in" and then the fuel economy gets way better. It took my Prius 5,2000 miles to get there. Pre break in, I was getting 36mpg at best. Post, and its hard to go below 40, usually getting 45-50.

 

Hi Bikesmurf,

What your are describing, is the jist of the real art to driving a Prius for commute fuel economy. The 5 stages need to be matched to the road conditions, during the warm-up period. I finished the last tank at 63.9 mpg, even with morning temps down as cold as 26 F during the tank.

When you start the car you want to pick a route that has a continually moving conditions except of a stop light for at least 5 miles. In the first morning drive, try to use secondary roads without allot of traffic, before I get on the highway. Even though I could get on the highway allot sooner. Getting into even slow-and-go taffic when the car is starting cold will cause the car to have to rewarm itself over and over. This uses allot of gas. Driving the car at highway speeds before its fully warmed up will use more gas too.

Secondarily, to get good mileage you need a temperature guage. In my car, once the engine gets to 70C, If I can have that happen near a downhill greater than 35 mph speed limit, I can glide that down hill. If its up above 73C, it wont glide. So, I try to get a route where the downhill is long enough that the car cools down below 70C, so when pulling up the hill at the far end of the downhill, the car warms back up to something less than 73 C. In other words, I choose the uphill speed to avoid going over 73 C. Then I can glide again. After that second down hill, however, the engine is going to go above 73 C. After which the car needs to get up about 76 C before it will glide again. The route I take has a average upslope at this time, so the gets to above 76C rather quickly. Then above about 79 or 80 C, the car wil not allow glides for a period of time, and all of a sudden the temp drops a few degrees. Only after this drop, and rewarming above 80 C will it be glide-enabled. Typically, when the car reaches this 79 C glide-enabled, I have a long downhill. And on cold days the car will actually drop down to 70C its such a long downhill. And so, the game to get back to 79 C starts all over. But with the engine compartment warm, it goes through the cycle in about 1/3 the time.

But, this game is not over yet. Once the car gets up to about 86, it will go glide-disabled again, until you get can get to a stop for a about 10 seconds. After that, and getting the engine up to 88 C or so, then it will be fully warmed, and will glide on demand.

This time of year with the starting temps so variable, its very difficult to figure out a route that matches this pattern.

During the summer, things are very consistent. And one can develop an optimum route. So, that when one is downhill, that car is in a glide-enabled temperature range/status, and when comes into a stop light, its the right time for the Stage 3/4 transition.

This is definately more complicated than it should be. But I am no expert in emissions controls either. But that is why its done. Japanese styling tends to be "busy" and overcomplicated to western eyes. I think this might just be some of that expressed through the engine control