Colder weather has zapped my mileage to 44mpg

Using the 3 years of Classic Prius data I have collected, extracting JUN-DEC spreadsheet entries, the average comes to: 46.4

Using the 5.5 years of Iconic Prius data I have collected, extracting JUN-DEC spreadsheet entries, the average comes to: 49.1

Using the 7 months of 2010 Prius data I have collected so far, also JUN-DEC spreadsheet entries, the average comes to: 51.2

So, even though the outcome for this month of December was indeed 44 MPG like the topic here, it really doesn't mean much overall. It's just among the lows which fall below the average.

Don't forget about the big picture.
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During the summer we averaged around 48 MPG with mainly short to moderate trips. On road trips it was easy to achieve over 50 MPG in the summer.

Our last major trip in Sept. we got 57 MPG, calculated.

I just can't imagine the big drop in MPG's during the winter. The winter MPG's is my major disapointment.

alfon

 

Alfon, 10% of 20 mpg is a very manageable 2 mpg decrease.
10% of 50 mpg sticks out like a sore thumb.

But it is still 10%

 

I tried grill blocking last year. From my calculations, it did seem to improve things by 1-2 mpg. The distance is critical. If I drive 10 miles instead of my usual 5, I get 10 more mpg.(44 vs. 34 mpg). I park outside so an engine block heater is unfortunately just not practical for me. I do think most cars suffer from poor mileage driving short distances.

 

How much blocking did you do? Obviously a 5-mile trip may not be enough to warm the engine even with 100% blocking, but with such a short trip you would be pretty safe trying that.

Good to know that it can pay off on the trips over 5miles.

 

For those following this thread and my thread where I have been posting my MPG experiments during winter (http://priuschat.com/forums/gen-iii-2010-prius-fuel-economy/71937-influence-speed-temperature-weight-mpg-3.html#post1026228), I took 2 more long trips during the holidays, this time using a scangauge to monitor the water temperature and I concluded that:

The hwy winter MPG drop in the 2010 Prius is NOT due to inadequate engine warm-up.

In my two 360-long hwy-only trips (air temps of 33 and 11F!), the water temperature in my 2010 Prius reached 190F quickly (less than 5 miles from a cold start) and stayed in the 190-200F range all the time while cruising in the hwy.

I'm glad I did not block my Prius grill before getting the scangauge for my hwy trips because I'm sure that would likely have resulted in overheating. In fact, 2 other shorter hwy-only trips in my Honda Odyssey during the holidays (similar temperatures) revealed that the water temperature rarely gets above 190F and stays between 170-185F most of the time while cruising in the hwy, therefore, the ICE temperature during hwy-only trips in the 2010 Prius (20-30% MPG drop in cold weather) is actually warmer than the Odyssey (2-5% MPG drop in cold weather).

Amazing!

 

In those temperatures, blocking would not increase the observed water temps. Instead, the rpms (and fuel usage) would decrease because less heat loss means less need to turn the ICE in order to maintain normal operating temp and supply cabin heat. I, for one, never meant to imply that you were failing to reach normal operating temp, just that you are using more energy to reach and maintain that temp than you would with some blocking. Most of the savings will be in shortening your warm-up and in those rare cases when you are not on a highway, but there should be some savings on the highway and there will be no increase in water temp in cold temps.

As an aside, your 5-mile warmup is almost 2 round trip commutes for me, so you can see how critical the blocking is for me, even in spring and fall. No doubt that colors my perspective in favor of blocking, FWIW.

I ran full blocking on my Tacoma V6 due to all these short trips last winter, and left the blocking in until August (>100F) when on a long highway trip I observed water temp climbing from 190/191 up to 195, then removed it. The OEM temp guage never moved, of course; just watched the SG.

 

It will not overheat. The thermostat would open the coolant loop to flow through the radiator. If that's not enough, the radiator fan will just come on, like in the summer.

BTW, how did you measure 2-5% MPG drop in Odyssey?

 

What outside temp & driving speed?

195 is the hottest I ever see (with full lower blocking) while cruising on the highway with a very brief (10 seconds) hit at 197 while climbing a hill, even when it's as warm as 55 outside. That's no where near hot enough to overheat.
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Weather has been cold the last few days. Temperature -17C/1.4F during the day, not counting wind-chill factor. The consumption from yesterday's fill up is:

16.6km per Liter
or
39.65 miles per gallon

Not so impressive comparing to what is advertised but my BMW X3 would be a lot worse.

 

FYI,
Regarding to the engine coolant temp...

• green zone: below 203F, normal condition and controlled by thermostat
• yellow zone: 203 - 212F, trying to be cooled down by radiator fan
• red zone: above 212F, overheat range

Ken@Japan

 

What's advertised for temperatures so cold?

EPA here doesn't include conditions that extreme.
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Toyota website is listing it at 51/48 mpg city/Hwy. Compares to my reported 40 mpg city/hwy (at about 50/50 ratio) combined, it is not something that I would brag about among friends. Unfortuately, winter in Ontario Canada at 0 degree C or 32F is normal, and -17C or at 0 Fahrenheit isn't uncommon neither.
I wish all car manufacturers can also list their gas consumption with city/hwy ratio and at what temperature did they observe their ratings.

 

Just to throw my hat into this ring. I bought the car somewhere in the August time frame (maybe september?), and my 50 mile one way commutes usually end up in the 57-65 MPG range. This was with temps ranging from 55-75 F. Going into work is always lower, but it's more uphill.

I don't know if what we have for temps now here in NC counts as "cold", but the car reported 37 F in my garage when I started out, and 25-27F for the trip in today. It did far better than I would have hoped with a reported 54.0 over 51 miles. This is with pipe insulation over both the upper and lower grill. My speeds did NOT change (about 60 MPH, 65 on the downhills and through various merge sections where it's prudent to run closer to the PSL).

Anyway, color me surprised. I didn't think I'd be able to pull more than a 50 MPG over this trip today. 54 is stellar for these temps, IMHO. The MPG drop is about the same as my previous car, but the percentage is way lower. For comparison... my 99 Elantra was good for about 40-42 MPG for the trip to and from work in summer, and about 34-38 in the winter (no blocking). Now, if I could just keep the missus out of my car, I might have a shot at making a 60 MPG lifetime .

 

The thing is... it's not their test. It's the EPA's test. And the criteria and temps are available online... it's something like 75-78 F or thereabouts? The vehicle manufacturer is not responsible for those numbers.

 

Here is another NC guy throwing in his hat. I have been off the last two weeks of the year and my driving has been purely around town. My 49 MPG average dropped to around 40 MPG. The cold weather along with the short trips really cause the MPG to drop.

Driving my 26 mile trip to work today though, with about 20 miles being 60 MPH highway driving, the 1 minute consumption screen was showing between 50 to 55 MPG and this with the temperature showing at 23F. I was really surprised at this also after reading all of these posts. With the 55-75F weather in the summer/fall the 1 min consumption screeen would show in the 55-60 MPG range.

I have no problem with this, especially since I replaced a 15 MPG Jeep GC with the Prius !!

 

Sounds like another vote in favor of grille blocking...

 

Oh hell yeah . I had blocked the grill sometime in November, with the pipe insulation on the bottom grill only being half blocked. I took the car through an automated car wash and forgot about the insulation. I was at a loss as to why my consumption rates seemed way off the rest of the day, with one highway trip only averaging 48 MPG at 36 F over about 20 miles. It wasn't until I walked by the front of the car the next day that I noticed my insulation was gone. That pretty much sold the grill blocking for me as a very noticeable effect, and anything below 60-70 F is going to find insulation stuck to the front of my car... which also sparked the comment of "why do you always do weird @#$ to our cars" from the missus .

 

Those are overall estimates.

The cold testing is only a small portion of that and the temperture only goes as low as 20°F.

So, it is quite unrealistic expecting mpg anywhere near that high for much colder conditions.
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Interesting, thanks to you both. I may then block the lower grill in my next trip to see if there is any improvement at all with hwy-only driving. I'm sure some people here in the past have suggested that the Prius ICE never reach adequate temps during winter without blocking, even while cruising in the hwy and that is simply not true. It may indeed waste more energy to get there (above 190F) but the prius does it better than my V6 Odyssey, which I found remarkable. Cruising steady at 75 MPH in my Odyssey for 1 hour has failed to bring ICE temps above 190F unlike the Prius.