Having a ScanGaugeII this winter revealed something new. It never dawned on me that coolant temperature would be the trigger when the engine starts up for the heater. But sure enough, it happens the same way everytime. 145°F is that magic temperature. (aka: 63°C) Needless to say, this discovery has had me captivated all week. I feel enlightened knowing precisely how close the car to that threshold. It's pretty sweet! So... I'll be adding this info to the User-Guide. Anyone got any other related comments to include? .
I never noticed that specific threshold, but at 154F (per CAN-View) you have the theshold for stealth being enabled. At about 121F you have the threshold for S2 to start and the end of the initial warm-up phase. I usually leave my heater OFF until I get to around 170-180 ICE temp just so I have a buffer that the ICE won't run more than necessary even after a long glide and cool down of the ICE.
With my 2003, NHW11, I found the ICE would restart at ~63C but I could get the ICE to stop a second time from regenerative braking and slowing down and further cool down to 60C. However, ICE would always run once it reached 60C. My experiments with my thermistor hack revealed the ICE is unreliable until a minimum temperature of 40C is reached. Using my thermistor hack, I've operated my 2003 Prius with engine coolant temperatures in the 50C range. BTW, I've been testing the block heater in my North American NHW11 and found it of limited use. Typically, I only heat the block for about an hour before driving and the cost savings are modest. However, with the thermistor hack with a 45 second delay, I suspect the economics will change significantly. Best of all, the thermistor hack will work when I can't plug-in the block heater, like at work on running errands. Bob Wilson
SOOooo. . . what is the implcation for driving in winter with the heater on. Should one be paying attention to water temp, and increasing the length or power of pulses to keep the engine in a certain temp range? Or to time the pulses to when the ICE will be kicking on anyhow so that the power is used to power the car as well as warm up the engine. Or does it really matter, since the system will do its own thing? Or am I just suffering from a combination of OCD and cerebro-rectal insertion?
By leaving the heat off initially you reduce the air circulated around the ICE which pulls away some of the heat from it. You shorten warm-up time. Once warmed up though turning the heat on does little "harm" in most situations.
I see the same thing John. What bothers me is the engine usually starts while I'm at a light, due to the coolant temp slowly dropping, but while idling at the light, the engine coolant temp doesn't climb. It stays at where it was when the engine started, or continues to slowly drop, just more slowly. In other words, I could freeze to death if the light froze! BTW, the coolant will drop to about 40C while idling, if the outside temp is close to -18C/0F. It will stay there until you drive. Also, contrary to the excellent dissertation at Technofathom about the stages, I find stage 4 starts at about 65C, not 70. A small discrepancy, yes, but a discrepancy just the same.
Just got my Scanguage last week for my birthday, nice to see the data that the car uses to determine what it's doing. Before, I sometimes had trouble knowing if the ice was running or not! The first 5-minutes of my commute is mostly downhill, I usually leave the heat off until I get to a place where it's uphill for a couple miles and I know the ice will be running more, mpg sucks uphill anyway and engine temp will go up. This is also the place where the windows will start to fog up, I turn the AC on and it immediately clears. I think the more I learn about the Scanguage readings the more efficient I'll be. I too noticed the 145 degree threshold.
