It doesn't seem to make sense to me that after the ICE has been running and obviously warmed up that it needs to incur another warmup cycle just because the car was powered off for a 5 minute period ? Does the engine cool that quickly. If it does I understand if it doesn't cool that quickly it seems like a temperature sensor in conjunction with some minor reprogramming could be use to let the system know that another warmup cycle isn't necessary. There'd be less fuel wasted because you wouldn't incur another first five minute penalty that wasn't needed as the car's ice was still warm from the previous driving segment. Could some please explain to me why this happens or maybe my observations of what is happening are incorrect ? Thanks in advance
I don't know "why" as in "how did the programmers decide to do this"...the S1 phase is quite short after a brief shut off, but it's real and can have an impact on FE...if I'm going to be shut down for <5 minutes I prefer to leave the car in READY unless I have to shut it off.
The O_{2} sensors need to be hot enough to return the trim signal to the engine controller. This takes a bit of heat and the engine has to run a bit. With my NHW11, we're taking about just under a minute or about 0.1-0.2 miles. But I agree that I'd prefer to have the car be immobilized but engine enabled. IMHO, it would be great if there were some way to leave the parking paw engaged but the car in "READY." You want a type of transmission lock. Bob Wilson
The catalytic converter cools down faster than the engine and needs to be warmed again. Prius' design philosophy is to minimize emissions, which is not quite the same as maximizing fuel economy. As Evan alludes, if you have a 2004 or later Prius and plan to be stopped for less than 5 minutes or so, consider putting it in Park instead of shutting it OFF.
At any rate, in Pearl at least, the warm-up of the cat is only about 15 sec. or less if the engine was just running. If you have the interior heater or cooler on (auto A/C) it could be longer if the traction battery is down a bit or the system is calling for heat. This is a "hit" on fuel economy for sure, but not a big one. As the above posters said, you can leave the car in "ready" with it it "Park" (THAT'S what the park button is actually for!), and lock the door with the key when you step out (you don't actually leave the car on and walk away with it unlocked do you?). Be sure to first apply the e-brake firmly so as to not tempt it jamming the parking gear when you put it in park.
