I can't believe what I'm saying as I always say to start driving (slowly) to warm up the engine. Besides, who has the time? But, this AM, I was stopped as soon as I exited my driveway as big garbage trucks blocked my cul-de-sac street. The engine went through the warm up cycle as I waited stopped and later, I went through my usual commute. The thing is the commute ended at 67 MPG (indicated). I usually get "only" 60 MPG on the very same route, unless the engine is prewarmed before driving and I get exactly 67 MPG. I always clear MPG trip counter before driving on a daily bases. I need more testing to prove or disprove it. Has anyone seen that effect? I also see block warmer in my future!
I have seen in some of the Japanese data from Ken@Japan that is one of their practices. I've also helped a local couple go from 50 MPG to 58 MPG by suggesting they let the car 'warm-up' in place. But I agree it needs more study and there may be an ambient temperature variable. Bob Wilson
I've been doing this for three months. I have several intersections on the way to work that I use as checkpoints for displayed fuel consumption. Once I'm past the first 3 miles or so I'm doing as well or better than driving immediately on the cold start. It's also a much better feeling taking off with the engine contributing to the propulsion (and the battery freshly topped up).
I've identified these specific, cold-start, warm-up phases: catalytic converter light-off - ~50 seconds, the engine runs "open loop" using the stored fuel trim. The car uses traction battery at moderate acceleration. It can reach 40 mph and shifting into "N" results in high, instant MPG numbers. engine coolant warm-up to 60/70C - ~3 minutes, the engine is running "closed loop" but uses higher than normal fuel consumption rates. With each 10C increase in coolant, the Scangauge II shows a decrease in the gallons/hour. The car will shutoff the engine at a stop but otherwise runs. EV mode is possible but only to 9 mph. efficient power operation - the engine consumes 0.60-1.20 gallons/hour at urban speeds, 50 mph or less, and the engine will turn off automatically. This happens up to 46 mph but more reliably at lower speeds. 70F and higher cruise control speeds of 25-27 mph -> approaches 99.9 MPG cruise control speeds of 28-32 mph -> closer to 85-95 MPG cruise control speeds of 33-35 mph -> closer to 75-85 MPG During colder weather operation, I can see the instant MPG scale peg during the engine coolant warm-up by shifting into "N". But lately, I'm not seeing the same jump over keeping the car in gear and on level road, cruise control, speed maintained. During the catalytic converter light-off, I'm also not seeing the same instant MPG pegging. It is an area that begs further investigation and metrics. Near as I can tell, the warm-up costs consume the bulk of the fuel. This is where the PiP has the advantage of letting the engine warm-up at minimum fuel consumption while EV provides motive power . . . the short trip penalty. Bob Wilson
I had to work today and I started the car inside garage before driving, when I came back after brushing teeth, ICE was already off. It's hot these days, about 80F in AM. I got 63MPG in the first part of the commute, however, little traffic, and I drove faster, so this shouldn't count. At least there was no loss of FE with all that idling. It rained hard when I came back and I had to use defog of lot. The average MPG dropped to only 55MPG for today. Rats!
I don't think more than a minute of warmup (enough to exit stage 1a) is worthwhile. You can force the engine to start immediately after the Ready light by giving the accelerator a tap. I then fasten my belt, tune the radio, adjust the mirrors, etc. to spend the time.
...that would be nice but I am under impression PiP does not really solve the low MPG at ICE start-up problem.
If the ICE warm up while you are moving 10-15 mph, you can easily get 50 MPG. Above 25 mph, you can accelerate and still get instantaneous 50+ MPG. The PHV battery is more aggressive in assisting during the warmup.
Today I forgot to do the prewarming routine and got exactly 60MPG. This is what I will do. I will alternate prewarming days with no prewarming days for a nice study with controls.
Someone will certainly correct me if I'm wrong..... I was under the impression that the computer does not calculate mileage unless the car is moving. Thus, any gas burned while parked is just ignored. Seems like this would negate any assumptions or calculations made regarding warm up effecting MPG displayed.
The instant MPG calculation is turned off when the car is just sitting but it is my understanding that the trip A and B mileage are still being calculated accordingly.
The Trip A/B mileage is calculated strictly by dividing the miles traveled by the gallons consumed while the car is in Ready mode. Very early in a trip you can see the ave. consump. value decay as you sit at a stop sign with the engine idling.
You must have a different display than I do. Unless you're talking about the fuel consumption display on the NAV screen. The MPG display on my dash is "----" when sitting still.
Actually it recalculates when any gas is burned. In my UPS studies, I needed to know how much gas was burned at different power levels. So I would park the car with a value on the trip meter and note it. Then I would put the load on. After a suitable interval, an hour or so, I would get the decreased MPG and use the first and last measurements to calculate the fuel burned. Bob Wilson
OK, I have results of my "study" with 22 data points. Alternating idling warm up vs no warm up. Runs with AC on or rain discarted. warming up mean MPG 63.5 (range 58-67) no warming up mean MPG 61.2 (range 59-65) NOT STATISTICALLY SIGNIFICANT (p=0.09) But we have a trend of better MPG and at least not worse for sure! Not sure if the results will be similar winter time with longer warm up.
BTW, one day after the "study" was over I got the record high MPG (my highest ever) for this commute: 71.5 MPG. Guess what? Yes, I idled before driving that one. Sadly, lately, there is no time for it. I just start and drive (slowly first). Understandably, MPG suffers (barely 60 MPG).
We park in an underground garage at our apartment. Would we be better off sitting in place for the ~50 second S1a period or rolling slowly (<10 mph) while driving out of the parking garage during the S1a period? Is there any way to force the Prius to skip S1a? In our Fusion Hybrid I can force the car to skip its equivalent of S1a and go right to S1b which I've found greatly increases the efficiency in the FFH.
