Real driving MPG?

With the 1.6L engine, we've found one hour of block heater will save about 1 minute of warm-up time. Depending upon the cost of fuel, it usually saves enough to make it worth while. Since the 1.8L engine weights about 5 lbs more, we would expect a similar warm-up savings.

I think Wayne has published warm-up data with and without a block heater.

BTW, the first minute is pretty important:


Reducing the initial fuel burn provides a lot of benefit for the 1.6L Prius and folks are expecting similar results with the 1.8L.

Bob Wilson

 

First fill up today after one week with the car (left the dealer with a full tank): 400 miles/8.73 gallons to fill up = 45.8 mpg. AC on most of the time, about half city, half highway, no special driving techniques.

This is my first hybrid so I'm still learning...I expect to do better before the next fill up.

That is calculated mpg...the display said 48 average.

 

Trip from Des Moines to St. Louis to watch the Cardinals in my new 2010 Prius last week and got 55.1 mpg overall.

 

Do you have an estimate of the amount of fuel saved? How much power does the EBH draw?

EDIT: and if it saves so much fuel, why doesn't the Prius have an integrated EBH running from the HV battery?

 

Well after reading this thread I understand why I'm stuck at 49.5-49.6 mpg on the display on my first tank. Tires are set at 40-38 psi and I'm stuck with short trips between two-four miles as a normal operating procedure. The start up warm up of the engine is what is killing my gas mileage.

Still a hell of a lot better than the 20-21 mpg I was getting in my previous car.

 

From a posting Jan. 18, 2008 in "Prius Technical Stuff:"

Roughly a 5-9 cent savings for each day of use.

The HV battery energy comes from burning gasoline including road taxes. The grid power comes from a power plant optimized for efficiency. But typically we only get 1/3 of the energy from a gallon of gas from the engine running to charge the battery pack. It would be more efficient to burn the equivalent amount of gas in a heater under the engine.

Bob Wilson

 

I drove 460 miles on 9.24 gallons that gave me a average of 49.78 MPG..

Fuelly isn't reflecting my MPG correctly...

 

Bob,

Thanks for the figures. I have calculated the extra gas use for warm up in winter (Dutch winter that is, temp ~0 C) to be 0.05 - 0.1 l, based on my first 5-min block, which usually is around 2.5 l/100 km higher with a cold engine. The first block takes me to the first traffic light, a distance of 2.5 km: 2.5/100 * 2.5 = 0.0625 l. But the engine is not fully warm at that point, so will continue to use a bit more after that point. That is consistent with your observation of 0.02-0.025 gallons.

What does surprise me though, is the amount of electricity required to heat up the block: 0.44 kWhr. Others have talked about heating the block for 2.5 hours or more. Do you always start your EBH 1 hour before you leave?

You say: "The grid power comes from a power plant optimized for efficiency. But typically we only get 1/3 of the energy from a gallon of gas from the engine running to charge the battery pack." Power plants may be optimized for efficiency, but still get typically 40%. Add grid losses and you're down to less than 40%. I don't see a big difference there.

 

I start it anywhere from 30 minutes to an hour and a half. What I'll do is when I first wake up, I'll bundle up enough to plug in the car and then come back in to make breakfast and get ready for work. Also, I tend to do this when the temperature is 40 F (5 C) or colder because of the nature of my 10 mile (16 km) commute.

The engine block heater (EBH) is a resistance heater, a constant energy load. As the heater runs, the engine block gets warmer and heat losses increase. Eventually, the block gets warm enough that the heat loss equals the heat added. Experiments have shown that is about +35 C after 4 hours. The engine block temperature will stay +35 C relative to the ambient temperature. There is a formula for this relationship:

To my eyes, anything after the first hour is pretty much a losing proposition. We are still paying the same electrical cost but the engine is not getting that much warmer.

So this is what it looks like in practice with my NHW11 Prius:


To my eyes, an hour is affordable but anything much longer shows evidence of diminishing returns. I don't fault anyone else who wants to maximize their block temperature before they drive off. In a colder climate or with different goals and objectives, a longer heater time may make more sense. Living in Alabama, we don't really have sub-freezing temperatures to deal with.

This is why I've been thinking a combustion heater may make more sense. You'll get all of the heat energy from the fuel to warm up the engine block but there is a better solution: co-generation.

Bob Wilson

 

Thanks for all the info Bob, appreciate it.

And of course, in very cold climates, an EBH is worth the extra comfort and safety. If you can recoup some or all of the cost & energy by improving your mileage, then that is a bonus.

 

Bob, it's time to update the graph to reflect the new 1.8L enigne vs. the 1.5L of your Classic.

Wayne

 

I have a GEN II 2006 Prius that we've put just over 62,000 miles on it since new. we live in the Northeast and my wife commutes 60 miles a day. We get mileage in the high 40's in winter and in the mid to high 50's in summer. Our average over the three years we have owned this car is 51 MPG. Also worth mentioning is our ONLY repair has been to replace the HID headlights. They both failed several months apart. Toyota paid for the most recent one as it has been determined that (especially on the 2006 model year) these are failing in epidemic proportions.

 

I did an unscientific test today, 7.4 miles in each mode with similar roads and traffic conditions (NE and N Atlanta...hilly and stop and go).

Normal mode: 61.5 MPG
Power mode: 60.5 MPG
Eco mode: 58.7 MPG*

*Eco mode's test ran out with a pretty good hill climb, prior to this it was at about 71 MPG but dem's the breaks.

Point is...not a big difference in modes *IF* you drive the same. I actually think I could have met or beat the regular vs. power modes had I not had to accelerate around a slow moving vehicle and then brake and regather speed after a clown stopped in the left lane to cross over to enter a plaza on the right.

 

Actually I've noticed your posting some data. But it won't be until December-February that freezing weather will return to Alabama. By then I should have instrumentation.

Bob Wilson