Call it an experiment...

I'm about 65 miles into my current tank of gas. When I filled it up the temps were in the high 30s/low 40s. Cold enough that we were in fairly heavy coats, but warm enough that the AC didn't really seem necessary. I did run the AC for one 5 mile commute when I had my wife with me b/c she complains when it's cold at all, but other than that I've been driving this tank without the AC--even when it was in the mid-20s coming home from work at 2am last night.

And guess what....even with the fairly cold temps over the past 24 hours and several sub-5 mile/sub-10 minute commutes I'm getting 51mpg currently on this tank. It had been up to 53mpg before my 28 degree commute home from work last night. Before this tank my previous best start (ie. milage after the initial 10-20 miles was about 48 mpg and that got trashed when we were hit with a cold spell.

I have to attribute the entire mpg gain to the non-use of the AC. It's a little chilly in the car at times, but since we're already bundled it's really not bad--I don't wear gloves. The car stays in the garage and it's about 50 degrees in there. I did wear gloves coming home last night, but it really didn't feel that cold.

I'm not saying folks shouldn't use AC, but I'd give serious consideration to keeping it off when it's not particularly hot or cold out--I think you'll see a major difference in MPG.

It's a little cold today with a high expected at 27 degrees. But the rest of the week should have highs around 40 with an upward trend toward 50 degrees by early next week. I'm hoping for big things this tank!

 

Well, there are some points to clarify. My lifetime mpg is 44.3 mpg. My best tank was 46.2 back in Oct. when it was warm, but before the Prius was really broken in. I don't really consider my driving 'city'. It's more 'rural'...part highway, but with several points about 1-2 miles apart with stop lights that I must stop. I have to do frequent 5 mile commutes to drop off and pick up my kids at daycare and school. The area is pretty hilly.

But, as far as tips. This post shows a big one...there's a pretty significant hit on MPG with the AC running. If/when you can leave it off, do so. To me it doesn't seem like it's a good idea to turn it off and on several times during a trip as it will work harder to warm the car (or cool it in the summer) to the preset temp. I also leave the AC (in winter) at either 65 or 67 degrees. I find that quite comfortable when I'm wearing a coat/jacket for driving. I'll probably aim for 74 or 75 degrees in the Summer when I must use it.

Tire pressure is a biggy. I use 42f/40r--44f/42r is probably more efficient, but since 44psi is the maximum the tire is rated for and b/c pressure will increase with higher tempertures I prefer the margin of safetly since I don't check it every day.

Check you oil level....if it is even slightly above the 'full' mark have some drained. This is not an uncommon problem--the engine with new filter will take 3.7 quarts to fill...well, oil comes in 1 quart bottles. If they check and see that the dip stick isn't registering at 3 quarts they're likely to add the full 4th quart which will over fill. That can both decrease fuel efficiency and cause harm to the engine.

Brisk acceleration is another factor, though I'm skeptical about how much of a factor it is. When you can safely do so briskly accelerating (your goal is about 4000rpm on the ICE) gets the ICE up to it's most efficient range (most power for fuel used). If you try to nurse it along but the ICE is turning you are at a lower and less efficient rpm--it will take you longer to get up to speed and burn more fuel getting you there.

When you reach your desired cruising speed use the cruise control, even if you're not going a long way. Any slowing and reaccelerating or speeding up then slowing down will impact milage. The hybrid system is happiest at a steady state.

Keep speeds modest, don't over accelerate, speed demon, etc. I find myself staying at or just slightly above the speed limit now days and it really makes a difference.

Anticipate stop lights and turns. Get off of the gas as early as possible when you think you're going to need to stop. This allows both a prolonged regeneration and for the ICE to shut off that much sooner. An added occasional benefit is that as you're rolling up to the light it may change for you before you get there so you don't have to come to a complete stop. Static friction is the most difficult to overcome and if you're able to roll through with a little speed you save on the hard consumption during acceleration from a stop.

Short trips, esp. when the engine can cool b/w stops, is a killer too...it's very hard to do better than 25-35mpg in the first 5 minutes. So even if you get 50mpg your second 5 minutes you're still going to average out to 35-40 mpg for that 10 minute period.

Factors you can't control: Cold temps will take a big hit on MPG. I'm supper stoked about the 50+ mpg I'm seeing--I've maintained that today despite 23 degree temps and fairly winding conditions and very short commutes (4 seperate 5 mile trips with time for the engine to cool between each trip). I think that in the spring with warmer temps I could easily hit a 55 mpg tank, maybe better if circumstances permit. It'll drop back down in the summer when using the AC becomes necessary, of course, but I'm still pretty excited.

Wind is another factor. Humidity, road conditions (esp. when wet or snowy), elevation you drive at, hills/mountains, etc. Contrary to what the press will tell you frequent stops and starts, esp. every block or two, will be very hard on your mpg. The 'city' the EPA ratings come from allow much more modest driving distances and start/stop cycles.

If you have a PDA, download Wayne Brown's THS II Simulator http://www.seawell.net/Prius/PalmTHS2/THS2HiRes22.zip and find out what your local conditions are and try out what it suggests you'll get for mpg--my experience is that it's frighteningly accurate. Still, it can tell you a lot about what you should expect. Physics is the biggest determinant of your mpg. All the other little tricks above are relatively minor factors, but they do add up over time and may give you a 1-2 (maybe more) mpg edge over 'regular' driving with factory tire pressures.

Hope that's informative--it took a long time to write!!

:idea: Danny, if you're out there, maybe we need a thread or specific place to have stuff like Wayne's Simulator and an FAQ with an expanded answer like this one we could refer people to. I bet it's not the last time this question is asked.

 

I don't think having a link to his information would be a problem.

 

Think of the words "Air Conditioning" more literally rather than mistaking it for meaning "Air Cooling" the way we, in the US, traditionally use the term. WRT the Prius A/C refers to both heating and cooling (and dehumidifying). Since the temperture is set to a specific temperture when you turn on the A/C it will automatically heat or cool the car depending on whether the preset temp is cooler or warmer than that preset.

So, turning off the A/C turns off all heating/cooling/fans, etc completely and thus creates on drain, what so ever, on the system.