Typical affect heater has on MPG?

I turn my heater off at stop lights, otherwise the ICE keeps running. In situations such as a cold start or going up hill-let 'r rip.

 

As I recall, we can set them to celcius:rockon:. Think that would help?

 

You can also drive with ECO mode on - this will prevent the ICE turning on ever so often.

 

I wait until the car is warmed up before putting the heat on Auto and leaving it set at 68.

My results:

Temp Trip Distance MPG
27 35 61.5
34 38 59.1
25 35 60.1

My ride is varied w/ predominantly back roads driving and a 8 mile stretch of highway. Lots of hills, but generally downgrade going to and upgrade going from. I get to use the eco band probaly 95% of the time.

I'm sure it'll be worse if the temps were in the teens or single digits. But I'm not driving with a jacket and gloves on in my car. I'll drive conservatively, but I'm not going eskimo.

 

I've found the same, also the fan can kick it in.

I don't mind the temp at 65, for me it's a constant battle to keep the windshield defogged with a car full of people.

 

HI works great with ECO when set to manual.

The engine will shut off when engine coolant is above 114°F, which is quite cold by coolant standards. Sitting in silence at intersections with the heater still blowing (medium fan) is really nice. You can cruise along up to 46 MPH without the engine that way too.
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I live in a low humidity area, so I let outside cold air into the cabin when I first start my trip on cold mornings, to keep the windshield clear. Once the ICE has warmed up to 140F or so I turn on the cabin heater, usually in 'auto' mode at about 70F. Most of my radiator is blocked, so 5 minutes of driving is more than enough time for the ICE to warm up.

If my hands and feet are not cold, I can tolerate moderately cold (25F) weather for a couple of minutes without much fuss. The absolutely *best* way to deal with cold winter mornings is 20 minutes of exercise before I leave the house. Then the cold weather is pleasant.

 

happy new year boys and girls.When running the heater I set the the system to recirc mode. Not sure it makes a difference but common sense says it should since I am not sucking in outside cold air and heating it verses heating warmer air in the cabin already.
Thoughts ?

 

Recirc leaves things more "moist" in the car, which can create issues with defogging.

 

I was thinking of wiring up something that turns the heating system off when taking the foot off the gas, and re-engages AUTO on when the gas pedal is pushed beyond a certain amount (the engine on region). Maybe could do it by tapping into the wiring behind the AUTO and OFF buttons along with micro-switches (or equivalent) near the accelerator.

 

Since this is my first winter with the Prius I was wondering what some of your strategies are to using the heater. I have a few ideas but I would love to hear what others have to say. Thanks!

 

When traffic permits, to warm up more efficiently, I try to accelerate in the 5/8 HSI area, instead of faster acceleration and then letting off the gas pedal, causing the engine to continue to run inefficiently without producing any motive force. I also see that when in Auto mode in the heater, once the fan indicator reaches 2 bars or so (depending on interior air temp), that this is my sign that the engine will shut off when I lift off the pedal in ECO mode. Remember the shut off engine temp. threshold is higher when not in ECO mode. In the first mile or two of my home-bound commute I sometimes turn the heater system to OFF. The advantage of toughing it out a bit, is a faster warmup, better mpg, and one appreciates more, the reward of comfortable heat a little later on in the drive. When almost fully warmed up and going uphill or traveling at higher speeds, I up the temperature into the high 70s F and go out of ECO mode, so that I can extract the excess heat the engine that would otherwise be directed outside the car, so that when I get to the next slow down or traffic lights, I can turn down the temp to the upper 60s F, and the residual heat will hold me through a traffic light cycle without an engine on event.

 

I keep my heater at 22c and don't care if the engine is running to keep me warm. Whatever happens, I'm still using less fuel than in any other car out there (with the exception of the plug ins).

 

Well...sort of. If the ambient temperature is low enough, even with grill blocking I observe that running the heater can drive engine coolant temperature way down, and this affects engine efficiency a lot.

The effect is bigger than "how much gas do you need to burn to make that much cabin heat". When the engine gets cool, oil viscosity goes up increasing friction, plus there's the whole Carnot cycle efficiency limit - cooler heat engine = less work extracted.

On cold days, I keep an eye on water temperature, and only run the heater when the coolant is 80C or hotter. When I've stolen enough heat to cool to 79C, I shut the heater off until I can get the engine temp back up where I want it.

 

... I am in the Grumpie camp we just heat to 70F and don't worry about it...but the thing I notice in the winter the traction batt is usually in the green start-of-charge, I think due to ICE running more to make heat. If I put on rear defrogger (eg; snow storm) then HV batt gets more drain.

 

I dress warmly and set the temp on low for the first few miles. That way I can keep the windows clear while I drive. The cool breeze isn't a problem-fogging windows are a problem!

 

What I find is that when it is really cold (and it gets below 0 here in Nebraska), these are the best techniques for maximizing your mpg's, for those of you without an engine block heater (not possible if you park outside like I do).

(1) Start the car and go. No need to "warm up".....if you do, the Prius engine will run for a very long time, especially with the heater on, using about .01gal/minute. The worst thing to do with a cold engine is rev it high (freeway @ 60mph or more). Since very few people live right next to a freeway, your car will warm up as you begin to drive. Make sure engine has been running at least 3-5 minutes before hitting highway speeds......I am counting stop lights in those minutes, since engine will run when cold. You'll know engine is warm when it shuts off automatically while heat is OFF.

(2) Keep "recirculate" on. The engine will work harder and warming the cabin will take longer if it's bringing in cold outside air. Eventually this will cause your windows to fog, but that's your signal to switch off recirc since it means your cabin is comfortable and the engine is warm enough, so that it can quickly heat even super cold outside air.

(3) You are MUCH BETTER off keeping temp LOW but fan HI. It took me some trial and error to realize this. If I had the fan LO and the heat HI (85), then the engine was running all the time.........even at stoplights..........trying to give me that warm air. But if I turned the temp down to 70 and the fan at one of the HI settings, I am just as comfortable. And it's much more efficient, since running the fan takes NO fuel (it runs off the battery), but running the engine to get warm 85-degree air does. Trust me, when its 10 degrees outside, 70 feels just fine!

 

I believe if the temp is actually set to "HI" instead of say a degree lower, this invokes a different algorithm that keeps the engine on a lot more. I would say do some trial and error with temp set to 84F with low fan speed vs HI with low fan speed, to see difference in engine off time. I suspect putting the fan at high speed with lower temp has the side effect of a wind chill, and also lowering the coolant temperature at a faster rate, perhaps somewhat mitigated by the lower temp setting which mixes more non-heated air with the hot. It would be interesting to know how much of the engine heat on a 0F day is given off within the engine bay. If that is a high %, pulling the heat faster from heater core to heat the cabin (84 F and high fan speed) may be a good strategy as the heat will otherwise be dispersed to outside via the engine body itself acting as a heatsink. One can then, turn off heater then when it just about to reach the engine on temp threshold.

I understand Toyota has the "HI" setting engine algorithm for extreme conditions, where maximum heating is required and efficiency is of lower priority as engine stays on much longer. Also disengaging "ECO" when in "Auto" mode will allow the system to automatically raise the fan speed to a higher amount, further maximizing extraction of heat from the heater core.

 

One more thing I forgot to add:

(4) When you first get into car on a really cold day, as mentioned above, the engine will run, even at stoplights. Thus, you are getting "free" heat since the car is warming itself up (and also charging the battery, which as others have posted, means you get more green batteries in cold temps). Thus there is no mpg 'penalty' for heating up during these first few minutes, and you probably want to get warm fast anyhow!
After a while, though, when the engine has warmed up (you can tell when it shuts off at stoplights, with heater OFF), then a good way to maximize mpg is to turn heater on/off corresponding to when engine is on/off (orange arrows). That way you are again getting 'free' heat, since the engine has to be on anyhow during that part of the drive to provide power. If, however, you are at a stoplight (or running in EV mode (yellow arrows)), then turn heater OFF, if you can stay comfortable. If it is uncomfortable, then at least set the temp lower (70) and the fan higher. That way, the engine is less likely to turn on......and no mpg penalty. In short, avoid using the engine as your personal heater...but don't hesitate to 'steal' its heat when it has to run anyhow.

 

Not sure if this has been covered, but anyway:

My observation is that it's not just heater being on or off that triggers the engine. The temp you've got it set to is just as instrumental. I was sitting at a red light with engine turned off, and heater temp at maybe 20 C. Ticked the heat up .5 degrees and engine went on. Ticked it back down to 20 and engine went off. Did it several times: quite consistant.