Just bought my Prius - early mileage questions

You being at 77 mph and colder weather is what's hurting your mileage. I'd never even heard of Shenandoah Valley until I looked it up. I don't know how accurate this site is but I see temps at History : Weather Underground. Without knowing your tires and tire pressure, I don't think your mileage is that far off for 77 mph in the winter.

To take from the http://priuschat.com/forums/gen-ii-...answer-these-questions-esp-if-youre-new.html:
- What are the approximate outside air temps?

- Is your oil overfilled? (i.e. above the full mark on the dipstick)

- Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).

- What are your tire pressures?

At Consumer Reports Cars Blog: Tested: Speed vs fuel economy, they did some tests of mileage vs. speed. Too bad no Priuses were in there. Bob Wilson at http://priuschat.com/forums/prius-hybrid-news/68731-consumer-reports-mph-vs-mpg.html did some work on mph vs. MPG but he's not active on PC anymore. He also never owned a NHW20 (what you have). He only had a NHW11 (1st gen) and ZVW30 (3rd gen).

I don't recall if he or anyone else did a lot more work on plotting mph vs. MPG for the NHW20. Bob was pretty thorough (another example at http://priuschat.com/forums/gen-iii-2010-prius-fuel-economy/64355-puzzle-75-mph-vs-80-mph.html). But again, he never had a NHW20 and the ZVW30 does better on the highway than the NHW20.

The behavior you describe about the "flashing back and forth" on the MFD is normal when using cruise control on the highway. I wouldn't worry about it.

Since you mention "fighting to get the car to stay around 50mpg", you're not going to get 50 mpg at 77 mph on level ground a 2nd gen Prius (well, maybe w/a strong tailwind). It sounds like you have some expectations set based upon EPA ratings (48 city/45 highway, 46 combined) or what people have self-reported. If it's based on EPA, you might find http://priuschat.com/forums/other-c...uth-about-epa-city-highway-mpg-estimates.html insightful (average speed on "highway" and "high speed" portions is only ~48 mph).

There is so called "superhighway mode" (SHM) but as I posted at http://priuschat.com/forums/gen-ii-...y-mode-alternative-65-75-mph-range-hints.html, when I lived in the Bay Area, I found it completely unsuitable for the speeds I needed to maintain. It would be even less suitable for you and you'd need a http://www.scangauge.com/.

 

I live on windy coastal plains. High winds and high speed driving are what lowered you mpg. The Prius and most other hybrids get there best mpg's in city/urban driving at speeds between 30-60mph where the electric assist is at its most efficient.

 

You purchased your Prius 2 days ago, and this is your first long trip? So I guess my advice would be don't worry about "early mileage". A better picture of the mileage you are capable of routinely achieving will come with time.

If you already haven't looked it up, this site has a wealth of information in regards to tips for maximizing Prius gas mileage. Tire Inflation, Driving Techniques, Etc...

You did say you had your cruise control set at 77...well any vehicle will be more efficient at 65, 60 or even 55 mph than 77....

 

Only winds within about 15 degrees of your tail help mpg. Head and side winds are killers. What you have described and achieved is reasonable, even with more experience.

When you get a chance, reset trip B and check your cruising mpg at any or all of 50, 55, 60, 65, 70, 75 on reasonably flat ground with light wind and warm temps. Then compare to bobwilson4web's graph. You should be in the ball park.

Have a little patience. Good luck.

 

Stop analyzing and just drive the car for a few tankfuls then report back. Your current results mean very little and no one can really give you advice until you establish a baseline.

 

It's absolutely the high speed, unfortunately there's no way around that. I once got caught in a traffic jam in my Prius on the highway, and had to book it like a wild librarian after to make up for lost time. Driving like a maniac and at comparable speeds to you I got 43-44 mpg for the 50 mile or so highway trip, so 39 mpg for high winds and hills is not surprising.

It's also best to get used to the car like many have mentioned. That being said, here's my two cents anyhow. :-D

Get up to speed fairly quickly on the highway. Pick a top speed that's nice and slow, let's say 68 mph or so (it's all relative, isn't it...). Don't try to gently edge up to speed, because then you'll always be accelerating in that 35 mpg range like you mentioned. Once you're there, back off slightly on the accelerator, and if you're on a flat or downhill you will likely barely maintain speed or lose a little, but your mileage will shoot up into the 70s or more as instantaneous mpg. This is called Super Highway Mode, read up on the threads others have provided. Since you want to stay relatively quick, just accelerate back up to 68 mph or so whe you hit 60 mph.

Secondly, for the downhills, don't coast with regen braking (not sure if you meant that or not - that's with your foot off the gas pedal completely). Instead, let up and reapply just a hair. You'll see the yellow arrows come on from the battery. This is called Warp Stealth and is brilliant on downslopes or before taking an exit. This is not a huge drain on the battery as you might think, but you're not using fuel while also not slowing as much like you would with the foot off the pedal. It is the most fuel efficient possibility on the highway and should be used as much as possible.

What it boils down to is get to speed, then find the minimum amount of pedal needed to keep the thing moving. Slow slightly to take advantage of various states described above then reaccelerate lightly, etc., and enjoy the better mileage.

 

19-28 mpg seems pretty low. I usually get 25-30 mpg when going up hills. How long was your drive? Wind and going 75 mph could have an effect, but I don't think that it would be that bad. I'd test it out and record the fuel mileage for a couple of tanks, but it does not sound too good.

 

Are you driving up hills with comparable grade at comparable speeds?

 

Yes, to the original poster I'd confirm that I regularly get as low as 19 instant mpg while climbing tough hills, and average on those I'd say more like 23-25. I wouldn't be concerned by those numbers.

 

High wind and high speed is an MPG killer. 40 MPG is probably about right under those conditions.

Do a bit of "around town" driving and you'll be averaging up around 50 MPG no problems.

 

The engine has to work a little harder sloshing through the extra oil. It may also hasten the dirtying of the throttle plate and the MAF sensor.

Check tire pressures at least monthly, and check them when "cold" (that is having driven no more than 1 mile in the previous hour). Keeping the tires at 42/40 PSI front/rear makes it easier to get better MPGs.

 

Let me admit upfront, a disadvantage and a philosophy approach I "try" to embrace for myself. I currently do not own a Prius. So I hesitate to give direct commentary...as to what an "experienced" driver would get under simular situations..that's better left to the experienced drivers...

I'll make a semi-exception...and say given my time spent in Prius Chat..and my knowledge of Prius..I don't think the numbers you present, given the conditions applied, necessarily raise any red flags that you have a problem.

So I feel confident in presenting the idea that you simply do not worry too much about initial numbers based on an early road trip, under less than ideal circumstance.

It's almost like medicine. "If" you have a problem? It will get worse, and/or become undeniable..

At this point? I'd say averaging almost 40 mpg..on a long road trip, with hills, wind and an average speed of 77 miles per hour...is IMO actually pretty good.

My guess...is you are fine. Wait for summer, look up tips and advice here..and I bet you can just consistently improve...

 

Interesting. I just did a trip DC>Richmond>DC - long grades but less incline... and averaged 54. Accelerating up hills was down near 25 mpg, I tried to allow myself to decelerate as I went uphill to not drop much below the 25-30 range. As soon at I crested the hill I backed off the accelerator all the way and then re-applied until the MPG was in the upper 70s to maintain speed / build speed back until I could coast.

My average speed was probably lower 70s mph, same day, similar temps, maybe slightly less wind, definitley milder hills. The car has mid-life Michelin (?? low resistance?) at 42/40psi.

 

^^^ That's pretty good MPG for the speed you were traveling.