Well, I'm at roughly my mid-tank level using 91 octane and my Energy Monitor currently reads 28.7 mpg. A item that's noteworthy is that I've never been able to get the EM above 28.4 mpg this far into a tank of gas using either 89 or 87 octane. So, various thoughts come to mind: a) my amateur attempts at hypermiling have suddenly improved (highly unlikey), b) the energy monitor reading is off somehow due to the change in octane level (possible), c) luck, statistical fluctuation (most likely candidate), d) getting better FE with the 91 octane (wishful thinking).

I guess time will tell... the current FE number is moot anyways... The weekend is coming up and a trip to SF should sink my numbers back down to reality... it typically falls back to about 27 mpg...

 

Well, despite my spouse's and my nephews' and my sister-in-law's best efforts to drag down my FE by blasting the A/C on high all weekend (was sizzling hot in the SF bay area) and keeping their "are we there yet" impatience placated with 70-75+ mph speeds, my FE only dropped modestly from 28.7 mpg to 28.0 mpg, at least according to my Energy Monitor.

When I finally filled up my tank with about 14.5 gallons, my distance was 390.7 miles, putting my FE at 27.0 mpg (about 4.4% lower than my EM).

That compares with 26.3 mpg from my previous tank where I used 89 octane => about 2.7% higher with the 91 octane... Some improvement, but not very significant. If I compare 27.0 mpg against my baseline of 26.1 mpg, a 0.9 mpg difference is about 1.5 standard deviations... so starting to get statistically significant, but not conclusive.

Qualitatively, it does seem to be easier to maintain higher FE numbers with the 91 octane, but the numbers don't conclusively support this (and I suspect psychological biasing is affecting this as well). So, I see some preliminary evidence to indicate some improvements, but that's stretching it at this point. I'm trying another tank at 91 octane to see if I get consistent results.

At the end of the day, how you choose to drive under what conditions seems to be the main driver. A weekend of A/C with 70-75 mph speeds can easily erase a week of hypermiling gains.

Is it worth the extra cost? I calculate that I would need to see improvements in FE around 3.2% to break-even. So... unlikely, at least from a strictly monetary point-of-view. However, is the extra cost worth the improved responsiveness and "smoothness"? Perhaps... on the fence on that.

 

Seeking advice on HiHy driving

Have had a 2006 HiHy Limited for ~ 3 months with 2,500 miles.

Average today is ~ 24mpg - highway is actually ~ 27.

The issue is that recently (ie - last two tanks), I have been getting considerably worse milage for city only driving, ~ 18 mpg. I have been running the AC higher (live on the very hot East Coast) and city driving is usually trips that are less than 1 - 2 miles each way.

Any advice to get back up to the ~25 - 26 that I was getting in the city on the first 2k miles.

Thanks

DC HiHy

 

I too live on the hot (recently rediculously hot) east coast (NYC). During the height of the heat I was looking at 16-17mpg tank averages. I drive mostly local streets.
What I realized was that my FE was dependent, in part, on the level of charge of the battery. With the heavy A/C use, my onboard temp was reading 100-102, the battery was draining and as a result forcing the ICE on to recharge it.
On the highway I had no problems because of the excess power being transferred to the charge cycle. On the city streets however, the ICE was coming on frequently to charge the battery when I didn't need the power from the ICE.
I had two choices: turn the A/C off or find some excess power. I decided to drive more agressively in the city and my FE improved about 10-15%. There are also tips on maximizing A/C effectiveness on other threads.
So in essence, pay attention to your battery level and avoid having the ICE do the charging while idling/coasting.

 

So, I finally got a decent FE reading for my 3rd tank using 91 octane. This, despite two long trips, one to SF and the other to Carmel (A/C included). When I finally pulled up to the gas station, I recorded 419 miles on 15 gallons, which translates to 28.1 mpg. (BTW the energy monitor read 29.5 mpg, the typical 5% discrepancy I have grown to expect).

I knew I had something a little unusual when I passed 340 miles and I my fuel gauge had not reached the 3rd marker yet, which is where it's usually at at that distance. I was able to squeeze another 50 miles (i.e. 390 miles) before it finally crossed the 3rd marker.

So, I think I have a little bit better understanding of how some of these hypermilers with the HiHy get such impressive numbers. At least from a person that started off with typical FE around 25 mpg, here's what I've noticed:

• All that Pulse and Glide propaganda... hogwash. At least my experience with the HiHy and at least for FE's between 26-28 mpg, PnG is totally irrelevant and in fact, a little dangerous always watching that stupid Energy Monitor. Maybe PnG becomes a valuable technique if you're able to hold speeds at 35 mph and are going after +30 mpg in the HiHy.<
• Speed is a FE killer. Need to try and keep the HiHy in that sweet spot between 35-45 mph. Moderate traffic congestion is your friend. On the expressways, I try to drive behind a slower car. On the freeways, ideally you want to keep your speeds < 70 mph. 65 mph is good, even slower is better: again moderate traffic congestion is ironically your friend. If you need to keep at 70 mph, what I try to do is let up slightly on the accelerator once in a while to let the electric motor kick in.<
• Acceleration appears to be another FE killer. I've come to a compromise (if I want to have +26 mpg FEs) that I can't expect a heavy SUV to accelerate with the same response as a normal passenger car. I can do it, but it comes at a heavy price. So I find a sweet "spot" for acceleration where I'm accelerating very smoothly but hear no grumbling from the ICE.<
• A/C really sucks... literally in terms of bringing down your FE. It doesn't seem to have much of an impact when you're around the 24-26 mpg, but the higher the FE, I seem to notice the bigger impact it has in knocking those numbers down.<
• 91 octane, at least for me allows me to ironically drive more slowly by making the experience more comfortable. I'm able to accelerate comfortably from a stop without any ICE grumbling... just smooth as silk. Also, when I'm in that sweet speed zone 35-45 mph, the HiHy just feels remarkably smooth and responsive with the 91 octane. I dunno, maybe it's psychological, but it seems to be working for me...<

Another trick I've learned is that even if you are having a crappy tank, you can still make up a lot of FE as long as you have at least a 1/4 of your tank left (i.e. 3rd marker in your fuel gauge). Just for that remaining 1/4 tank, exercise major constraint in acceleration and moderate speeds. I've been able to recover from 26 mpg => 27.4 mpg (EM reading, the actual is 5% lower).

Anyways, I hope this helps others who may be wondering how in the heck these guys can get +28mpg on their HiHy. It's doable and there's no real magic: moderate speeds, light on the acceleration, keep it smooth. Don't bother with that stupid Energy Monitor; squeezing all electric... forget about it, I think it actually may be detrimental to your overall FE because it drains your batteries too much...

 

Nice writeup Han. Everything that you've said is true and parallels my experiences.

One possible thing that you did not mention is the effect of oxygenated fuels on your mileage. In California you have no choice (10% ethanol everywhere) , but in other states it is possible to purchase and use 92-94 octane 100% gasoline, and that may have a positive effect on fuel mileage for those of us who are able and willing to use it.

 

Thanks Han! I'll second chucko's comments re: parallels to my experience.

Your comments on the A/C are dead on. We have finally broken free from a heat wave (in Michigan terms) where the temps were in the mid to upper 90's with humidity around 60-70%. I had to keep the A/C running between 4/5 to 5/5 most of the time. Doing so dropped my mpg to the mid 24 range.

I have tried the P&G approach but it doesn't work well for me during my commute to/from work. The next step for me is to try to find fuel w/o the 10% ethanol content to see what kind of impact (if any) it has on mpg.

 

FWIW, I find that 10% ehtanol has about a 2MPG impact, as does running the A\C (basic HiHy). I look forward to stopping the A/C (I'm in PA). I don't have a lot of options on ethanol, since we are in what is considered a high pollution area. My recent MPG of about 27-28 should improve back to the 30 range we experienced whan we first got the HiHy. Overall, I am still satisfied with the MPG figuring the vehicle size. For over 5000 miles we have averaged 28 MPG, not bad. It is way above what I averaged with my previous vehicle.

 

On the issue of the impact of ethanol and other "oxygenated reformulated gasolines (RFGs)", I found an interesting article that contains a Wisconsin on-road fuel economy test, (albeit sponsored by Chevron):

http://www.chevron.com/products/prod...h_Rvw_chp1.pdf

The study claims: "When the results for all the road tests of all the vehicles were combined, the average fuel economy of the three oxygenated federal RFG gasolines was 2.8 percent lower than the average fuel economy of the conventional gasoline"

Now, the study does include different types of RFGs including MTBE, ETBE and ethanol. So, the vehicles using the ethanol mixture may be worse than the overall average, but statistically speaking it can't be much worse. So, my 28 mpg (if ethanol were to blame) could have been about 28.7 mpg. Namely, let's say about roughly ~1 mpg higher. It's also possible that the affects of electric hybrid assist could have made this ~1 mpg even more significant, say 20% or so to about ~1.2 mpg. I guess folks in CA will never know... I'm not aware of any gas stations that do not include ethanol due to the regulations here. But good to hear if there are any...

The article also has a nice table that summarizes various factors that affect fuel economy (FE) for regular conventional cars (it's in Figure 1-7). As we have empirically determined, speed, acceleration and A/C are roughly equal and signficiant contributors to impacting FE. They report reductions in FE between 20-25%. Idling/warmup also is a big factor: another 20%.

-Han-