2016 Gen 4 Two ECO vs 2011 Gen 3 Two on the highway

Yesterday I took my first highway trip in my new Prius Two ECO, a roughly 60 mile run to Springfield MA, 5 hours wait (for paint protective film and tinting), and return. Mostly on divided highway, where I noticed differences between my Gen 3 and the new car which may be useful. I'll try not to repeat too much of what has already been posted about differences in warmup and local driving.

(1) Compared to my Gen 3, the battery feels like it has a lot more oomph. The car will move along gas engine off at much higher speeds and up steeper inclines. My Gen 3 was 5 years old, so perhaps its NiMH battery had weakened?
(2) The Gen 3's gas engine restarted exactly when the load reached the line marking the midpoint of its range. The Gen 4 has a bit of latitude there.
(3) It will go into battery-only at far higher speeds, >60mph, than the <46mph that the Gen 3 was limited to.
(4) It will coast in N up to at least 70mph with the gas engine off. So this becomes a possibly useful highway tool, for example if the battery is fully charged and you don't want the drag of regen slowing you down.
(5) Here is the big one: Cruise control is a bad idea because it never shuts down the gas engine, even under conditions where the car would happily run with the gas engine off if cruise control were not set. Perhaps this is because it never lifts off the gas completely, and this is the "trigger" the car needs to stop the gas engine?
(6) Subjective, but it seems that shutting the gas engine off requires a very deliberate lifting off the accelerator and depressing it lightly. So I have to constantly remind myself to do that if conditions seem right to go battery-only. It seems to me that the Gen 3 would shut down its gas engine on its own "initiative" under conditions of light load.

Incidentally, (5) and (6) are some of the reasons that autonomous cars will need a lot of programming to match the MPG that a live driver can attain.

The averages were 76.3mpg on the way there and 83.0mpg on the way home, nearly identical route in opposite direction. I was quite pleased with that until I read that the average mpg in the 2016 Prius reads 5% high, just as the 2011 Prius did! I have not run a full tank through it yet so I'm not sure, but it was probably more like 72mpg and 79mpg actual.

Conditions were: mostly at 55 +/- 5 mph. It includes a warmup from cold (car is parked outdoors overnight) and from 85F coolant temp when I started home. Ambient temp around 60F on the way there, 70-75F returning, not much wind, humid, occasional drizzle both ways. OEM Toyo tires at 45psi.

One of the best summer highway trips in my 2011 netted 76.8mpg indicated over 140 miles (I found a photo of the display), or about 6mpg less than the 83.0 on my return trip yesterday. The EPA highway ratings for the two Prii are 48 and 53mpg, a difference of 5mpg. A surprisingly good correlation.

 

Thanks, I'll try those things. I was at 50-60mph yesterday so always above the 45mph "barrier". Most highways around here have lots of mild up and downhills, so I try to take the downhills engine-off and uphills engine-on (and charging the battery). More or less.

All of this is new. With the Gen 3, no matter what I did at speeds >46mph the engine was always running so cruise control was fine.

 

I'm still exploring that. Definitely above the 46mph limit the Gen 3 had. It seems to be more load-limited than speed-limited as the Gen 3 was.

At least from my viewpoint it's an improvement in almost every way from the Gen 3. Less space to store stuff inside the car, which is forcing me to cut back on the junk I had in the Gen 3, not necessarily a bad thing. Though it would be nice to have space under the trunk floor for a first aid kit and a set of jumper cables.

Methinks you need a test drive!

 

Ditto here. I use a Scangauge set to display RPM as one of the four readouts, and RPM did not go to 0 with cruise control set on that run. I was not paying attention to the green EV icon. You're right that around town when not using cruise control the green EV icon correlates with RPM=0. I have highway trips to do Thursday and Friday so I'll check out cruise control again on those runs.

 

Good point. I'll look at the GPH reading as well.

 

I took more highway trips and have to revise what I said earlier. I was wrong:

When the "EV" light goes on, the Scangauge shows RPM=0 and GPH=0.04, and I can feel the gas engine shut off. The 0.04 seems to be a sort of placeholder. I always saw a minimum of 0.02 in my Gen 3, so I assume these placeholders are to avoid calculations using a zero value, which might cause problems in the computers?

More importantly, cruise control does not LOCK the gas engine on, at least not completely. Monitoring the greenish curved load bar, one sees that the gas engine kicks in when the load rises to the line marking the midpoint (50%) of the range, and shuts off when the load drops below 25% (assuming that the coolant temp is high enough and other parameters are satisfied). This happens whether the cruise control is ON or OFF.

So say I am are driving along with cruise control ON and the gas engine running with load >50%, say going up a hill. As I crest it, the load drops, say to a steady level somewhere between 25% and 50%. As long as the load remains 25-50%, the gas engine will continue to run. If the downhill is steep enough, load will fall to <25% and the gas engine will shut off, contrary to what I posted previously.

However, if cruise control were OFF in the same scenario, assuming I am alert enough to notice (not always!), as soon as the load drops to <50% I could lift off the throttle for a second or two. Load momentarily drops to <25%, gas engine shuts off and I go into EV. Then I can reapply (electric) load via the accelerator pedal, and the gas engine will remain off as long as I keep my foot light enough to hold load <50% (for as long as battery power lasts.

I still think I get better MPG with cruise control OFF because I can use EV more, at least in the gently rolling terrain around here. But I have to be paying attention to kick the gas engine off when possible.

I apologize for the confusion, I think I have it right this time!

 

For most purposes I find cruise control to be too militant in keeping a precisely constant speed no matter what. Especially if no traffic is behind you, letting speed sag approaching the top of a hill can improve MPG since speed can be regained on the downhill after the crest. And you can build up momentum near the bottom of a hill to carry you along onto the next hill or level stretch.

I'm still figuring out the Gen 4, but in the Gen 3 it can help MPG to coast in neutral on the highway. According to the ScanGauge, the GPH when coasting in neutral is about half what it would be while coasting in D, so therefore the MPG roughly doubles. At highway speeds the Gen 3 does not shut down the gas engine even in N, so the savings could be even greater for the Gen 4 if it will shut down the gas engine while coasting in N. Another advantage of N is that one can coast down gentler hills that one would have to drive down in D.

Obviously if the battery needs regen or if the hill is so steep that the car would pick up too much speed in N, it can be left in D to take advantage of the braking effect of regen.

In the Gen 3, I used the cruise control on the highway a lot because the gas engine would never shut down. So I'd roll along in cruise control and switch to N when I came to a downhill.