Colder weather has zapped my mileage to 44mpg

Glad to know I'm not the only one who say so...

Let's face it. The Prius does deliver fantastic FE and I really recognize the good aspect of the HSD technology. The problem IMHO is: everything has to be so perfect to attain great efficiency on it. My expectation for the 2010 Prius was to get a lifetime MPG a bit higher than EPA estimates because that’s the way it has always been with any of my past cars. I, for several occasions, found myself mastering FE in my Prius back in the summer. I could "score" consistently and considerably higher than EPA no matter the speed, regardless if it was pulse and gliding slowly on the back roads or cruising at 75 MPH on the interstate! But the winter is bringing my lifetime MPG to such low levels, unlikely to be compensated in the summer until it starts dropping again in mid-fall. To me, the disproportional drop in cold temperatures should be made very clear by Toyota and dealerships up front. No wonder the car was launched right at spring and before summer. I know there are ways to minimize the effects of cold temperatures and ksstathead has done a great job explaining some this in his last post, but how about the ones who just want to drive it just like any other car, without compromises, without wondering about if another trip to the home improvement store to buy more foam pipe for grille blocking is needed, without slowing down to a ridiculous pace, without thinking about if letting the cabin to freeze may be necessary, without over-inflating the tires, and I could keep going on and on…

Obviously I’m not cut out to be a proud Prius owner… sorry.

 

68 MPH average (indicating faster travel at times) resulting in 36.9 MPG in conditions well below freezing is bad?

What do you hope to achieve by complaining here? We have already documented the effects of seasonal change heavily.
.

 

Thanks! Excellent data accurately captured:

I appreciate appreciate the grill block photo. There are two styles:

1. open inlet, back block - easy to implement, it means air is channeled into the inlet and bleeds out the sides. This potentially has a tendency to increase drag from vortex formations at the left and right edges as well as lower lip. These bleed energy ... think parachute.
2. closed inlet, front block - flush with the bumper surface, no air is trapped and bleed through and out the inlet. This preserves the air momentum and lower drag.

This block was made from a piece of house insulation with the foil barrier on the outside and beaded styrofoam on the inside providing compression strength. Packing tape held it to the inlet. Now I use a split water noodle that achieves the same effect without the tape residue.

In the first case, the snow and slush increased the effective air density for higher aerodynamic drag and rolling drag against the tires. The data is good and useful because it includes the 'wet' conditions including snow and slush on the highway.

The second case, dry conditions, is also important because many folks do not realize the importance of air density on aerodynamic drag:

What is not often understood is the same velocity with higher air density will push the Prius into less efficient power regions. What this means is a speed of 68 mph can easily require power settings closer to 75-80 mph. At 80 mph, I measured 39 MPG at a temperature of 62F:


I fully understand your concern about cold weather performance at highway speeds. The recent cold snap in Dixie has shown that urban speeds 35-50 mph, in dry conditions, our ZVW30 is showing closer to a 10% mileage drop.

Since you use "Fuelly," which I think allows access to per-tank data, you might find similar latitude, non-hybrids, and look at their per-tank mileage over the same interval. What this will do is get a clue to the impact of cold weather on non-hybrid vehicles.

Another option would be to rent a gas-only vehicle and use it for one of your long distance drives. This would give you something to compare against the ZVW30.

Hybrid skeptics have history of using high-speed, winter driving for Prius vs <insert other> testing. The most recent example was "Green Human" with their Portland to Portland test. But there was another test a year or so earlier from Car and Driver (?) or Motor Trend. It is only at high speeds where aerodynamic drag predominates and gas and diesel engines are working closer to their design limits that they become competitive.

Bob Wilson

 

I understand your disappointment. This complaint should be directed at the EPA, not Toyota. In the U.S., the EPA requires auto companies to report the official EPA mileage and wording: "Your mileage may vary."

Tom

 

Thanks Bob! Very nice...

Do you think my traditional foam pipe blocking could then have resulted in increased drag? Looking at all my 26 trips recorded so far compared to my last ones with the block, it does appear that the block may have had a negative impact instead of helping. Of note, this week I’m having the opportunity to do some low-speed back road driving, the same driving where I used to get 65+ (MID) right after I got my Prius before I even started recording MPG in my iPhone app. In my first drive this morning with the block in place, I only did 52 MPG... so still a 20% drop from the 65 I used to get... my point being… maybe the block is not really helping at all!

 

I would be very surprised if the block had any noticeable negative impact. Instead, what this shows is that there are a lot of uncontrolled variables in the mileage equation: Change something and rerun the test - mileage will likely go up or down. Change it back and run the test again - mileage will once again change, and often in a random direction.

The factors controlling mileage are complex and interrelated.

Tom

 

Thanks for understanding. But Toyota does know very well how the mileage drops in the winter... and dealerships likely have a clue too.... but it seems very “convenient†to "hide" that important piece of information and blame EPA for not recognizing it... would you agree?

 

Thanks for posting those pics. Judging from the salt on your bumper, you drive in harsher road/environment than me. I thought my Prius is dirty!

I still think your MPG is lower than expected.... especially for the Gen3. There is another possibility that I can think of. Did you hit anything on the road that may cause misalignment?

 

My last car was a 2001 Galant. EPA ratings were 25 highway, 17 city. Living where I do now and doing the exact type of driving I do now, I averaged about 19 mpg when doing local driving and about 23 on highway trips. This was in the summer, winter, spring and fall. Changes to mpg due to temperature made very little difference, if any.

I got my Prius in November. The first tank did about 46 and it has been steadily downhill till my now average of low to mid 30s for local driving, mid to upper 30s for highway. Thats a huge drop from the EPA estimate. I don't expect to meet or beat EPA estimates but I do expect them to be close.

Would grill blocking help me? Maybe. But why should I have to mess with a brand new car? Would driving uphill and keeping out of the power zone help? Maybe again but I can't drive at 15 miles per hour on a 35 mph road and have a string of cars following and tailgaiting me.

All these fuel savings tips that I have found here are great for the person who wants to make a hobby of squeezing the last mile out of a gallon of gas. The average person does not want to take a brand new car home from the showroom and start blocking the grill or inflating their tires to 100 pounds or driving at dangerously slow speeds.

I like the car except for the low gas mileage I get. Something is very wrong here. Not sure if it is the EPA testing method or the design of the car or some of each but the actual driving results should come close to EPA estimates. My last car did in all seasons and past cars have as well. Its just this car that fails so miserably.

 

I suppose an incredibly naive buyer could be mislead by the EPA figures, but unless someone had never before made a major purchase, I don't see how anyone could be surprised. So much information is available, especially in these days of the Internet. It is common knowledge that the EPA figures are only a metric.

Tom

 

I drive way too much to keep my Prius clean outside in the winter... it's just not worth washing it. My car is very clean where I have control, which is inside. I get rid of any unnecessary items inside it and keep the cabin clean all the time.

I have been thinking about misalignment because I lost one wheel cover for no specific reason. Did not hit anything apart from the usual periodic bumps in the WI hwy (I think those are for drainage, not sure). It is not obviously misaligned when I cruise in the hwy but I may be missing it. Maybe I should check it.

 

Tom, very true, and I did know about Gen 2 having a big MPG drop in the winter. This was classic. The word was spread across the community. My colleague next door has a 2007 Prius and she warned me about this. She also warned me about the rattles as a matter of fact. But, back on spring of 2009, my dealer and Prius chatters truly believe the problem was solved or was greatly improved for gen 3. If it was improved, I can't imagine how gen 2 was...

 

Remember that the EPA estimate is 48mpg highway, and uses a test pattern totally different from what I would consider "typical" American highway driving (70+mph, 1hr+ with no stops). Even so, with the stock tires & hubcaps I was consistently getting 44-45mpg (in temps around 20F) before putting on the snow tires - which should be easily offset by the 55-60mpg I will probably get in the warmer months.

And even after adding open-spoke wheels and snow tires, I seem to be beating your numbers... So, methinks something isn't right with your car (above and beyond the impact of lower temps), and for high-speed driving that's more likely to be something with aerodynamics and/or rolling resistance.

Did anything at all happen to your car (esp. the front end) in late Sept / early Oct?

 

Excellent. That paragraph captures my whole rationale behind how I I find the Prius a very poor value. Nicely put.

It makes it hard to like it when its major selling point is the gas mileage...

 

I had to replace the back passenger door back on Sept I think but that should not have resulted in FE drop... besides, I have got great mileage after that anyway until the temperatures started to drop...

 

GM has no problem designing a whole campaign around 230 mpg for volt. So if it has say an 8 gallon tank I should get a range of 40 AER + 230 x 8 =1880 miles without stopping for gas, right? Wrong. The 230 is a completely meaningless number that the EPA may sanction (it remains to be seen). So, no, Toyota is not hiding anything, nor blaming the EPA. The car performs as advertised.

Either something is wrong with your car and/or your driving habits are not as favorable in this car as the EPA test cycle. Or, maybe your spring/summer/fall results will get you back close to EPA.

 

Not if I drive it like a normal car without worrying about what I have to do to prevent a MPG drop upon minimally adverse conditions...

 

I have not done the experiment, yet, but I'm pretty sure a flush block is more efficient than a recessed block. My current, NHW11 block is a split water noodle that extends about an inch further than the surfaces of the bumper. I am pretty sure this avoids the worst of the vortexes that form on a recessed block.

I've been planning to 'do the test' this winter and this week is good enough. Cold air makes it easier to measure aerodynamic drag effects. I'll post the results here and at Ecomodder under a dedicated thread.

Bob Wilson

 

It must take a huge hit to lose the trim ring. Are you running without one now? It suppose to improve the aerodynamic especially at high speed.

 

Detail please.

Since I am a huge supporter of JUST DRIVE IT, which is simply driving along with the flow of traffic, what are you doing that's different?
.