MPG Impact of Heater

The Prius heats the cabin with engine coolant, just like any other car. And as long as you're not using AC, not much of a dent.

 

You will notice a slight drop in MPG during the winter months, but that is really due to the winter fuel blending. All vehicles suffer from this, some worse than others.

I usually set it around 76 or so and let auto do it's thing. Everyone has their own temperature they like. Play with it until you are comfortable. If you use no heat and or no a/c you will get the best MPG. But where you are heat will be a given just like A/C is a given here.

Best of luck to you and enjoy your v

 

This is correct. When the weather is sub-freezing the ICE can run much of the time purely to make heat. The higher you set the inside temp, the higher the system will keep the coolant temp, so lowering the temp saves some fuel.

Best choice is to use auto mode with the hybrid system in ECO mode. This will limit some less economical HVAC functions, will lock out bi-level vent mode too, and may also change how the defroster responds (in terms of when and how much A/C is called for).
Mostly, the auto system control is smarter than the average driver, it really is a set it and forget it system. Just keep the temp setting low in the winter and higher in the summer.

 

agree with all above, plus, the engine has to run longer to warm up, and more often to stay up to minimum temp. so even without heat, there is some drop in mpg's. i used to notice about a 20% drop from ideal conditions to the coldest days, all things considered.

 

Stop beating around the bush guys. Winter weather and heater kill your MPG as much as 30%. Your 44mpg city can get as low as 30mpg. In winter, with heater on, you will get worse mpg than summer with AC on. The Prius engine is very efficient. It produces less heat than any other cars. Plus the engine shuts off when you cost and/or come to a complete stop. Engine runs longer and uses more gas just to warm up and maintain the heat. You can block the grill and seal the hood/fender gap with foam tubes to trap the heat in the engine compartment. Even with all that, you'll only gain 2mpg back, 5mpg if you're really careful. It won't be nearly enough to compensate for the heat loss of cold winter and heater on. I get 50mpg with 50% upper/ 95% lower grill block and 100% fender/hood gap block without heater in 35-45f weather. 44-48mpg with heater. My area never get below freezing. In spring, I get 55-60mpg in 75-80f weather with cracked window. In summer, I get 48-52mpg in 90f-115f weather with AC on. These are calculated MPG not what the display says.

 

I can reliably turn the engine on/off at a stop, by ticking the cabin heat setting up/down. The threshold's around 21.5C I think.

 

Unless you use BOTH auto and eco modes, you don't get HVAC energy savings associated with eco mode. Keep the heat set as low as you can tolerate is the main thing. But if the blower is showing 3 or fewer pips you won't be using much energy regardless.

 

Gee it should be interesting to see how our 2010 handles southern Minnesota winters. Frankly, ANY car gets substantially less MPG around here in winter due to winter blend and warm up. I'm not too worried about it.

I have read differing opinions on the Prius in extreme cold. Some folks seem to think the car warms up *faster* than a traditional car..some don't. Of course, this is subjective. I'll chip in my opinion sometime this winter.

From what I'm reading, It does sound like grill blocking is a necessity though..I'll have to get on that soon.

 

Ignore the green light on the A/C button, it means nothing. The A/C compressor only runs when humidity is high enough to trigger it. For some reason the engineers decided to have it on all the time. If you manually force it off, you can't get the benefit if its super-humid.
If the system isn't keeping things warm enough for your taste, just turn the temp up.

 

When the AC light is on, the compressor runs, maybe 50/50 on/off. At least with a regular Prius.

 

That's entirely up to the conditions. In cooler weather it may not run at all. (in auto mode)

 

The only time* Ive seen the compressor stay right off is when I've got the AC button off (no light) and set Mode to Heat/Defog. Normally this will run AC, at somewhat lower wattage. But at temps maybe lower than 5C, it stops doing so. But with AC button depressed, unless temps are very near freezing, the compressor's running, off and on.

I'm monitoring AC wattage with Scangauge. It shows zero when the compressor's off, various wattages when it's running.

* Well, also, if you've got it on any mode but Heat/Defog, and the AC button off. Again, then the compressor will not run.

 

The New Car Features Manual for both the Gen 1 and Gen 2 (the latest ones I have, sorry) both rate the heat output identically at 5,300 watts. That refers to the amount of heat it can extract from the hot engine coolant when the heater is running full out, and by the TANSTAAFL principle, all of that heat will be replaced by burning fuel in the engine. On the other hand, if you weren't using it, a lot of it would just be gotten rid of at the radiator anyway.

5,300 watts is about 7.1 horsepower. If the engine's thermal efficiency is around 38%, then the engine is producing at least that much waste heat anyway, any time it is running above about 4.4 HP output - that's a bit above 5% of max output.

Of course the heater doesn't often run full out - it runs at whatever fraction of full out it needs to maintain the settings you prefer. Also, before the engine is totally warmed up, if the heater needs to run full out, it also kicks in the electric elements, which add about 700 watts in Gen 1 and Gen 2 (I don't know about other models). Ultimately, that power also comes from fuel in the engine, just by a different, mechanical-to-electrical route.

-Chap

 

Sir , it's second time when I turned on the heater , immediately the tank dropped to zero. It's JDM Prius 2010. I am uncertain whether it is the gauge faking it while heater is turned on or it's the real tank which drained as result

 

A seven year old thread, revived?

 

Has this car blown the head gasket yet?