Not an owner, but considering a Prius and have test driven one. My understanding is that the gasoline engine is not running at idle, but this morning (a humid) morning, I pulled up besides a Prius at a stop light and exhaust gases were obviously pouring out of the tail pipe. How can this be? Assuming a Prius buyer is not do dumb as to be sitting at a light revving the engine.
The gas engine will run under many specific circumstances but, when the car is stationary, chiefly when (a) The cabin needs heat (b) the car has just been started and the catalytic converter needs to be quickly brought up to operational temperature and (c) the battery needs charging.
It is not possible to "rev" a Prius engine. The accelerator pedal is precisely that - it makes the car go. It does NOT do this by varying engine throttle, but by a complex combination of activities that cause the electric motor to move the car, plus the gas motor - if needed. "Blipping" the throttle on a Prius has no effect whatsoever on engine revs when the car is in Neutral. This is unexpected and somewhat bizarre behaviour!
If the heater is set to max the engine will run until there is enough heat in the engine coolant to provide sufficient heat to the cabin heater to achieve the max temperature. In practice I think this means that it will run most of the time when the heater setting is max. Oh, and by the way, when it is the cabin gets VERY hot!.
I have to say I "just drive it" and let the car manage itself. If I'm cold I'll use the heat and if I'm hot I'll use the cooler. Don't see a lot of point in switching off the heater when the car is being driven - all it means is the heat generated by the engine will go outside the car rather than inside! Only if the car is standing for long periods will the engine be needed solely for cabin heat. In my case (UK) the difference in gas mileage between winter and summer is about 5 mp(UK)g I'm prepared to tolerate this for a bit of comfort!
Hi Chas, My wife just drives it and that is all fine. I find myself being tuned in to the little things. It is all good. Between us I find that I will get a couple of MPG higher (by this I mean that I generally push the tank's MPG average up a bit and she generally brings it down a bit to over-generalize).
I do find that the engine does indeed start up when I would expect it to be of, solely due to the call for cabin heat. There will be times when I do the foot trick to get it to stealth on a flat road and it just will not turn the engine off. Turning off the heat at that moment fixes that problem I have found.
Over the last 4 thankfulls we (together) have been getting 53 MPG average here in NJ. Tomes
1) initial warm-up - the engine runs until the catalytic converter and engine coolant are warm enough. The earlier, 2001-03 Prius can take over
5 minutes to get the coolant warm enough. Although the 2004-current Prius has a thermos, if it was sitting unused over a long weekend, the hot coolant could have chilled and warm-up would take longer.
2) other loads - depending upon the cabin controls, the engine may run to sustain coolant warmth or handle battery management. Defrost is notorious for causing the engine to run longer.
3) warm-up phases - there are some distinct warm-up phases that might not have been passed through.
A Prius engine runs when a Prius engine needs to run.
If you *saw* exhaust vapors then the engine and exhaust pipe were still cold and burning off moisture in the exhaust pipe.
Heater doesn't have to be on high for the engine to run, but the higher its set the more the engine will run when stopped. The defroster runs the A/C, and when sitting the engine will run about 1 minute out of 10 when the A/C depletes the battery.
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