Poor City MPG - 28!!!

<div class='quotetop'>QUOTE(lefat1 @ Nov 26 2007, 08:19 PM) [snapback]544488[/snapback]</div>

Hello fellow Southern Floridian. Temperature must have a lot to do with it, I've never had less then 45 mpg, with 3000 miles on my odo so far. Averaging around 48-49 with a 20 mile trip to/from work (40 mi. round trip)

The engine gets up to temperature within one minute (often way less) in the hot weather here, so it sounds like an engine block heater is a good idea for northerners, or letting it sit idling until the system warms up before driving off.

 

That sounds about right.

The temperature here is around 20-30 these days, I am doing 5-15 min trips and my current tank is giving me 37 mpg (only about 50 miles in this tank yet). In warmer weather, it's about 51 mpg when I do this type of driving. It will get much better in the spring.

 

That's actually one of the worst things you can do. It is much more effective to drive the car to warm it up than to let it idle. Fuel economy will also be better.

Remember, if the engine is running and you're not moving, you are getting 0 mpg!

 

<div class='quotetop'>QUOTE(drees @ Nov 29 2007, 12:39 PM) [snapback]545723[/snapback]</div>

I'm getting an average of 60.1mpg on my commute with my '08 Prius. I also drive 53MPH using cruise control. Worst average I've seen on a tank of gas was about 47mpg.

 

high 30's in winter-stop and go driving

I agree with those who range in the high 30s in winter. I too, have a short commute each day (6 miles), of which I can rarely go more than 30 mph with lots of traffic lights. In the winter I rarely do more than 37mpg and in the summer the low 40s.

Only when I can get the car on a highway (or hit that sweet spot of about 39mph steady, when the car goes straight electric), does my mileage improves. I still love Mr. Prius (that's his name).

 

a

Let me suggest you do a two part mileage test on your commute:

1. first two miles - use a trip meter and MFD for mileage
2. remaining miles - reset trip meter and MFD

What I've found is it takes about two miles to get the ICE coolant through 'warmup.' Thereafter, you should be getting 'hybrid' mode mileage. This two part measurement doesn't change the total but it gives insight to what the 'hybrid' part can accomplish after the car is warmed up.

Bob Wilson

 

The above story is true on a conventional vehicle, but it is not true on Prius.
Prius engine is not used to move forward for the first 56 seconds, instead only the motor is used during that period.
Sometimes, such motor only drives worsen your fuel economy.

Ken@Japan

 

Hi All,

For the short trip driving below 40 F, one would do well to grill block. Especially, if those 10 minutes trips are strung together with at most 15 minutes stops inbetween.

The car has the 35 mph stage 3-4a transition. One can glide in stage 2, but once the car is up into stage 3, which is the usual stage the car reaches after a some driving in these conditions, one needs to get the car up to 35 mph, to drop into a glide-able situation. Otherwise, even small accelleration invokes the ICE to come on. Once the engine is on, in stage 3, it wants to stay on. To get into a glide capable mode, one needs to get up to 35 mph. With the engine off, things cool down, and the car will want to turn the engine back on more readily.

So the trick in freezing and just below weather, in slow traffic, is to avoid accellerating, until you can be sure that you can accellerate steadily back up to 35 mph. Grill blocking will reduce cooling, so that the glide-mode will stay in-force for a longer time. One wants to time this so that the glides occur on the long down-grade sections of the road as well.

 

Ken, I don't follow you. I said that it is never more efficient to idle the car to warm up. If the engine is running, you should be using it to move the car as well. You are saying I am wrong and the engine isn't used for the first 56 seconds? Surely that must be a type-o, or some difference in the way the Japanese Prius operates compared to the USA Prius.

The Prius will automatically start the engine after powering in about 10 seconds. It will power off after some time, but not sure how long, but the colder it is, the more the Prius will run the engine to reduce emissions (at the expense of CO2 emissions).

 

Are you familiar what's going on during the initial 56 seconds, called stage 1a?
We observe the ignition timing is minus nine degrees of BTDC, or very late nine degrees of after top dead center, in stage 1a.
It means the engine can't produce any usable torque, and the exhaust gas becomes very hot to warm up the catalyst very quickly.
So, if you drive during the stage 1a, Prius goes to EV mode and the HV battery level will be down fairly quickly.

Ken@Japan

 

I think it has already been said but I find brisk acceleration isn't the mileage killer but hard braking is. Anticipate the next stop and lift your foot well in advance, you may even avoid stopping, maintaining more momentum, using less energy.

 

Drees, to elaborate a bit on Ken's last response: The ICE's total focus in that first minute or so is warming itself and the catalytic converter. So of course it's running, but providing little to no power for propulsion. Instead, when you accelerate during that interval, it's the battery that's powering the car. If your first minute of driving is under high-demand conditions (e.g., high speed or hill), then battery charge can be drawn down considerably, requiring the ICE to recharge it. Though your previous statement that sitting still with the ICE running produces 0 MPG is true, you'll pay for it later. (There is no difference between the US and Japanese Prius in this.)

I recently moved. My new neighborhood is favorable for immediately starting to drive; it's a steady gentle downhill in a light-traveled residential area. My previous residence had a quarter mile driveway, mostly uphill, with the first segment particularly steep. There, I would sit until the S1 stage passed -- i.e., the ICE cut off -- before moving. (An engine block heater shortened that stage to about 30 seconds.)

 

Thank you for the detail, I did not realize the Prius did this to warm up the cat. So if you floor it with a cold engine and the car in stage 1a, the car will stay in EV mode or will it finally let the engine do some work since you've exceeded some throttle threshold?

Can someone point me to where all the various operating stages are described?

So from what I can tell, the net effect on fuel economy from driving the car before it's switched out of stage 1a is break even. What am I missing that would cause worse fuel economy by driving instead of waiting?

 

Frankly, I'm not sure what would happen if you floored it in S1. I've never tried it.

Here is the 5 stages document.

It's not that driving in S1 will worsen fuel economy, it's high-demand S1 driving that could worsen it -- again, hills or speed. Substantial depletion of the battery charge, again, requires the ICE to recharge it. In doing so, the ICE is either running when it doesn't have to or supplying less power for propulsion than it might otherwise.

I should add that the fuel economy hit, if any, is small at best and would be tough to quantify.