Impressions after a Sierra trip

Well, I finally took my 3.5-month-old Prius on a nice long trip into the Sierras for a backpacking trip with some friends, and figured I'd write up some impressions, especially considering that many people here don't have many opportunities to drive in the mountains or on rough roads.

Overall, I got a somewhat disappointing but not awful 46.3 mpg (calculated) on the 500+ mile trip; a bit below my typical 50 mpg on the other 1000 miles the car has, but I suppose to be expected given the huge amount of mountainous terrain and large weight of occupants and gear (roughly 800 pounds, I estimate). I also spent lots of time at 3000-4500 RPM while going up mountains, at speeds both low (20) and high (50), which I'm sure was a leading contributor to my poor gas mileage.

The trip involved driving from about sea level up to about 8000 feet (Sequoia National Park), then down to 1200 feet and back up to 7600 feet, the latter portion on a 1-to-2-lane road with occasional sand/gravel stretches, and plenty of washboard and potholed surfaces.

The large elevation changes (especially from 8000 feet down, which was on a well-maintained road) meant that I had to use B mode quite a bit, which was an interesting experience. However, I noted on the less-maintained road that B seemed to do very little, other than burn gas; my ScanGauge indicated the engine wasn't going over about 1500 RPM most of the time, and I felt very little engine braking. My presumption is that B does not apply much drag at the speed I was traveling; about 15-25 mph, due to the steep slope, sharp blind curves, and the narrow and poorly-maintained road. Having more drag from B would have been nice, even if it only kicked in when I pressed the brake pedal. However, there was a little bit of rolling, and some acceleration needed after some of the curves, so I managed to avoid completely filling the battery most of the time, despite the 6400 foot drop (over about 23 miles). I also didn't feel too bad about blasting the A/C on max on this part of the trip, since there was an excess of energy available from regen, and a lack of battery capacity to fill.

It does seem to me (and I think this has probably been noted elsewhere, though I don't recall for sure) that B will cause the Prius to use more fuel, as it doesn't turn off the engine nearly as readily. Because of this, I switched back and forth between B and D fairly frequently in a few areas, so that I could stealth down gentle slopes, while getting extra braking on the longer, steeper descents when the battery was nearly full.

Traction, steering, and braking all performed well; some of the travel was on very steep sand and gravel, or rough surfaces, or braking quickly when another car came around a blind corner on the narrow road. I did not notice any dropouts in braking as reported by others, despite a good 23 miles of nearly-continuous braking at low speeds over a variety of slippery and rough surfaces, though I wasn't exactly trying to cause one, as doing so might've landed me off the edge of a rather large cliff.

The Nav system did OK; it differs somewhat in route choice from Google, and definitely thought that some roads were a lot slower than they really were when calculating the ETA. I was a little disappointed that I only encountered traffic in areas where there were no possible detours, but I suppose that's why the traffic was so heavy in those locations anyway. I'm still not entirely used to how to do everything on the Nav system, but I'm getting better. I feel like the interface could use some simplification, even if it meant losing a feature or two.

Thankfully, there were no tests of the PCS or airbags, nor did the resident marmots of the area eat my radiator cables or electric wiring, as they are known to do in the particular area of the park I visited.

Next weekend's assignment: a car wash, so she returns to her natural Blue Ribbon Metallic color from the current approximation of Sandy Beach.

Great story (and review), thanks for sharing. Any pictures of your trip? I've never been there, and would LOVE to see this pictures to go along with it!

As for the B mode and gas burning, my understanding regarding the engine braking is that while the engine does spin, to consume some momentum, it does not burn any fuel in doing so. If this is wrong, I would love to hear more about this, but that was my understanding.

Disappointing? "Poor Gas Mileage"? 46.3 mpg's given the description of your trip sounds excellent to me.

I guess I should learn, that many Prius owners have higher standards, but I always have to laugh a little when I read the "complaints" of 40+ mpg averages.

As a current non-hybrid owner, I would have to hitch my automobile to a team of horses part time to approach that mileage. So all I can say is...Hakuna Matata, given your description of elevation, inclines and weight of passengers and equipment 46.3 doesn't sound all that disappointing to me.

That was my understanding too, but if the ScanGauge is to be believed, is not the case; it was somewhere around 0.2 gallons/hour most of the time. Granted, I didn't always have the GPH gauge up, and I was paying a lot more attention to the curves and traffic than the gauge, so I can't say for sure if that was always the case, but at least some of the time it was. Worth noting though, that even at 20 mph, that's still 100 mpg, so it's a pretty small amount.

Oh, it was good, don't get me wrong. The other driver on the trip was a little jealous that she had to spend almost twice as much on gas as me for her Accord. But, on the other hand, given that most of the trip was on flat highways with cruise control where I've tended to average about 54 mpg indicated, and there were several descents where the engine stayed off for >30 minutes, I was hoping to recover a bit closer to my average. The first 233 miles averaged 51.37 mpg, while the last 391 miles (which included nearly all the hills) averaged 43.72. Climbing the hills tended to be a continuous 20-25 mpg indicated for >30 minutes, which is obviously what dragged the average down.

Pictures! I wanna see Sierra pictures!

I think the scangauge, at least depending on calibration of the fuel cut input, will lie, telling you fuel is going in when it is not. I think your fuel use going down mountains is zero whether in B or D. The engine spins above 41 (gen2)/45 (gen3) and in B mode.

The climbing uses a lot more fuel, of course, and any bicyclist will tell you that you never get back the time or energy of the climb during the glide down the back side. Thus, there is no way to get flatland mpg on a round trip to the mountains, because way more work is required, even though fuel use on the down is zero.

Rolling hills allow good results with proper technique, but long climbs are pretty tough. I think your results are stellar, given the elevation delta and weight.

Thanks so much for the insight into driving in the mountains. I am planning a trip to the southern part of Colorado in mid-Sept and was really wondering what to expect from the Prius. I will have many miles of flat, good roads before climbing to an altitude of 8500ft. Now I have some information on what to expect during that part of the trip! Thanks again.

What I found is both Prius injector timing and MAF sensors show a non-zero value even when there is no engine operation. The sensor "zero" is not really zero and has to be factored out when working with raw, recorded data. I don't know enough about the Scanguage to comment on it.

If on the descents you could keep your speed under 46 mph and not in "B", there was a good chance the ICE would have been stopped. However, once the battery fully charged, the brakes would have warmed up.

Personally, I prefer using "B" and moderating speed as needed with light braking.

Bob Wilson

Yikes, you people are demanding! ;-) I didn't really take any of the road (or the really dusty car), in case that's what anybody is interested in seeing. And they're all on everybody else's cameras, as mine isn't the latest and greatest of the group, so I left it behind. But, until I get a photo or two, you can check out Google Street View, which goes up to the park border:

[ame=http://maps.google.com/?ie=UTF8&hq=&t=p&layer=c&cbll=36.439779,-118.768194&panoid=SYv73_vE9_sRgh8AR-Ei7A&cbp=12,273.68,,0,-4.47&ll=36.43979,-118.776412&spn=0,0.049524&z=15]Google Maps[/ame]

The park (at least the part we were in) was rather more forested, green, and at a much higher elevation. We had to hike across a few remaining snow drifts up to about 5 feet deep, though they were melting quickly; a couple of the smaller patches were noticeably smaller after about 3 or 4 hours.

Funny you mention 'any bicyclist,' considering that was my only mode of transportation for a year and a half before getting the Prius... Never biked 500 miles in a long weekend though; I peaked at 125 in a day. Did cross lots of mountains, though - turns out there's a few different ranges in between San Francisco and Maine. Pretty awful Cd on my bike though, which makes it hard to get above about 50 mph. A high Cd isn't all bad, though; it made for a great day when I had a 40 mph tailwind for an hour.

It wouldn't surprise me if the SG showed the wrong info. On the other hand, though, the GPH goes to 0.01 when the engine is off, so it at least gets that approximately correct...

Most of my desire to use D instead of B came from the fact that when I was in perfect conditions to stealth glide, the engine would continue running. So I'd push lightly on the accelerator to reduce the CHG to zero, or even lightly into the "hybrid" range of the HSI, and the engine would still be cranking away. At that point, it was undoubtedly using fuel. Shifting to D would let the engine RPMs drop to 0.

Okay, got a few for your enjoyment... Not much of a distance view in most of these; it was fairly hazy, and there were lots of trees in the way. But that's what my weekend was like! It was a lot of fun - I dragged 6 others out into the wilderness with me for 3 days, most of them had never camped in the wilderness before.

Some other thread on the GIII points out that the cruise control works in D going downhill, sort of precluding the need for B mode. I don't know if that would make a big difference, because the car is still going to use the ICE as a Jake Brake once the traction battery reaches its highest allowable state of charge. I suppose it would depend on your smoothness of control in B mode, compared to the cruise control's in D.

This is not true. You can easily (with the correction cicumstances) find an uphill route that gives you "only" 25, 30 or 35 mpg, for example. Now you find a route back down, possibly a longer less steep road, and you coast all the way down. The downhill "miles" are more than the uphill miles, but the elevation change going up is the same as the change going back down.

Thus you "can" get very high mpg on a moutain road round trip that exceeds what you get on flat land. Most of the time people don't get this because the situation is different and/or they don't want to coast down at a low speed. It is just incorrect to say that there is "no way" to get this kind of mileage.

3PriusMike

Great story and pics! For us non-Prius types: What are B and D modes?

D is Drive and B is Engine Braking (akin to L on an normal automatic).

Thanks!

Some of my Auto Enginuity data suggests ~4,200 rpm is a peak rpm for maximum EGR. I suspect this may be the highest, optimum ICE rpm that should be used going up a hill. On power display, leave the smallest possible 'black' rectangle in the peak-power, red area. Nibbling solid and a little 'black' would work just fine and let the car and grade negotiate the speed. Anything slower would of course be even better but don't run a solid 'red line.'

Bob Wilson

Wow, you took your Prius up Mineral King Road? I've always dreamed of heading up there but never had the guts to do it with a low car like a Prius. Was it OK overall? Maybe I'll head up there in August after most of the snows are gone...

No trouble on Mineral King Road, and I have no doubt you could do it with a much lower car than the Prius, too. Wouldn't recommend it in ANY car if it were snowy, judging by the sharp curves and sheer cliffs a few feet off the edge... Luckily, it's closed in the winter for use as a snowshoe/ski trail.

I was perhaps slightly more worried about a forest road in the National Forest north of the park, which was more sandy and had some decent ruts in it, but no trouble there either. Just a little shock when the engine revved at 3000-something RPMs while crawling up a steep sandy incline at 5 mph - I think it was the first time I've dragged the battery low enough to warrant charging it.

And most of the snow was gone by the time we got there; at least, in the areas we were in. Nothing anywhere near the road, and only a few patches along our hiking path (around ~9000 feet; there's probably more at the higher altitudes).

Good to know, thanks! Can you recommend any decent day hikes (2 to 8 miles round trip)? After reading your post I might head up there this weekend for my birthday, haha. You can private message me if you prefer.

I could have told you that you'd have no problem on the trip with a GenIII. My GenII has been all over the Sierra (west and east slopes) and foothills with nary a worry and your GenIII is better equipped. I even drove it on 52miles worth of logging roads just to find a rare carnivorous plant!


*this was the smooth section

Well, there was this one time that Hyo Silver and I almost got stuck on the wrong side of a steep hill but that is another story.....