This page covers the warm-up and cold start characteristics of an NHW11, 03 Prius. However, thanks to a data record from Yoshiyuk Mimura, we now have some NHW20, 04 Prius warm-up data.

Stationary Warm-up and Commute

The following chart shows the fuel consumption and speed as a function of time. The vehicle was started with the daylight running lights off and in "P." After the car performed at least one "auto-stop," it was driven on my usual work commute route:

The normal commute route starts at the bottom, the southern limit, and proceeds to the northwest:

Initial Startup

You'll notice initially the ICE is spun quickly for several seconds before fuel flows and we see evidence of power generation:
There is an 80 second interval with fairly low ICE power requirement and then the injector timing drops. From this point on, the ICE is generating power to put a charge on the battery. This would include the self-discharge and other deficits. Within 180 seconds, the battery is charged and the rest of the ICE warmup continues.

Another way to look at warmup is ICE efficiency. Again, during the initial 80 seconds, the ICE runs 'full rich', a fairly inefficient mode:

Driving in this first minute and a half leads to high fuel consumption. It is better to wait until this mode ends before driving off.

NHW20 Warm-up Performance

Thanks to the thermos bottle, the NHW20 achieves warm-up in about two minutes. It also has excellent low-speed performance:

NHW11 Warm-up Performance

The earlier, NHW11 Prius suffers a longer warm-up due to the lack of a thermos of hot coolant. However, addition of an ICE block heater; transaxle oil pan heater; and use of Type WS transaxle oil, we may be able to achieve nearly the same warm-up performance of the NHW20. But for now, we don't have any pre-heaters and still use a Type T equivalent, Amsoil ATF:

We can also see the ICE efficiency over the same route:

Unlike the NHW20, the NHW11 will continue to run the ICE after the battery is charged. Although this helps warmup the ICE, it does nothing for fuel efficiency. This suggests a better strategy is to start the trip right after the initial battery charge completes.

NHW20 - NHW11 Performance

This chart combines the NHW20 and commuting, post-warm up, NHW11 performance. The longer USA commute also includes sections at higher speeds than the NHW20. The NHW20 achieves better warm-up and commute performance over the unmodified NHW11: