Hi Bob;

I can categorically say that the HCH-II is not that different from the Prius II and maybe your Prius as well in terms of the criteria for evoking eletric operations in extreme low temps. Indeed, these operations are not determined by the outside air temperature but instead mainly by the coolant temperature.

All I can say is that if we block the front air intake and use a block heater on both cars, each will warm up faster and remain warmer through an EV powered glide. However, in the temperatures we've been experiencing of -36C (-33F) both vehicles rarely will stop the ICE if driven for less than 20 minutes. But as I said, the coolant temperature is key, not the outside temperature. And if driven longer, the EV operations will occur (even if momentarily because of the accellerated heat loss).

On a side note, it appears that while the HCH-II will warm up slightly faster than the Prius, the Prius will retain the optimal temperature longer. I guess it is because the Prius II uses a "Thermos" reservoir while the HCH-II does not. Also perhaps, because the Prius ICE may have a higher mass and therefore greater heat retention ability.

Changing the "thermistor" to adjust the temp readings is something I am not too keen on doing. I see the technical merit, but unless it is implemented a little intelligently it could cause issues during the warmest summer months. If an software enhancement path was available then that would be preferable as we would have a more dynamic control over the thresholds.

So far, I've found that the combination of blocking the front grill and the use of a block heater can help a great deal. As you can see from my mileage on both cars I am actually able to sustain what I consider acceptable FE considering the temperatures and the relatively short duration of each ride.


Cheers;

MSantos

 

My '07 is in the same ballpark here in Colorado Springs. Last fillup was on 3 January and in the 280 or so miles since then, the computer has this tank so far at 37.2 mpg. The weather has been relatively cold, and the auto stop that in November was kicking in a few minutes from the house now doesn't kick in until about 10 minutes from the house.

I'm surprised at the big drop though for mine! Most of my driving around the Springs is definitely "urban", and the cold weather seems to have had a hit since I bought the car (new) in Nov 06:

tank 1 -- 44.0mpg over 307.6 mi, fillup 22 Nov 06
tank 2 -- 43.0mpg over 408.2 mi, fillup 3 Jan 07
this tank so far -- 37.2mpg over 280 miles

(all numbers straight from the computer)

- Mike

 

This isn't necessary, the heat is produced by the engine regardless. Using the heater just routes it to the cabin. Shouldn't affect the FE (ok, the fan might affect .00001 mpg).

 

Yep. The trouble is that having my heater or defrost on keeps the engine colder for longer, so even if I switch it off, the car won't AS to begin with. If I turn defrost back on after it does AS, this sometimes takes me out of AS b/c it gets too cold, as you say. So to sum up: I sometimes get pretty cold trying to get good mileage!

Actually, I do know someone in my area with a block heater: tbalano. So in theory I could do the test- but I don't think I need to go that far. I'm willing to concede that there is probably a difference, maybe even a substantial difference, if you use a block heater. My point was mostly just that HCHs without block heaters can still AS in the winter, which helps you keep your mpgs up. Not everyone knows that, as owlmaster's comment reflects. So to repeat: My HCH I actually WILL auto-stop if ambient temperatures are below freezing. It just doesn't kick in until the car warms up- which may be a long time if you don't have a block heater, I suppose.

 

Oops. Sorry to perpetuate false statements. I got my info from my dad. I might have to tell him about his and have him retest!

 

Thanks and good post, Leah. Not here to bash anybody as we're all family and no need to do that test but if someone wanted comparisons then we might have our first test subjects. With my Block Heater it makes it seem like the ambient temps are in the mid-40s rather than the low-20s as the car warms up in a short time and stays in AS for longer so I can tell it makes a difference. I have noticed that with temps below 15 F then THIS makes it seem like Winter a bit more than when temps are in the mid-20s in the morning. I pity those in Erie, Buffalo, Chicago, and Winnipeg/Manitoba. =) I got home with a disappointing 45.2 mpg today when it was as high as 47-48 mpg halfway through the day -- I had more hilly travel with traffic than anticipated so that hurt me for today. (I was stoked as the first trip of the day was another one of my test runs from an earlier thread and I went the 7.2 miles [mostly downhill] and arrived at 50.1 mpg at 17 F!!! Granted, the rest of the normal commute to the office was 23.1 miles at 47.1 mpg and 17 F which is more typical for me with the Block Heater.)

 

Hey Leah -- I wanted to ask you something. How do you use the Trip A and Trip B readouts for FE? I use Trip A for the entire tank average and Trip B for my daily average. When I start my day I get in the car, start it, and immediately reset Trip B to 0.0 (oh, I unplug the Block Heater from the extension cord first so I don't drive down the road towing our house). If you let the car idle and warm-up are you resetting the Trip meter BEFORE or AFTER the idling? I would like to know what your numbers are the next time you do this (and this weekend looks to be *verrrrry* cold for us so it would be perfect).

When one resets their Trip to 0.0 the readout does not go negative but I don't know if this time while the engine is running is taken into account.
For example, if you normally reset Trip B after the car has been idling and before your trip and you see 30.0 mpg at the first mile then 40.0 mpg at the second mile and ultimately 45.0 mpg at the end of your 20-mile commute then try resetting the trip meter before you start the car, then let it idle for 10 minutes, and THEN take your normal commute. I would be interested if the car kept an account of the loss of FE during idling and displayed something like only 15.0 mpg at the first mile then 28.0 mpg at the second mile and ultimately 40.0 mpg at the end of the commute. Better yet, reset Trip A before you idle the car and Trip B after it is all toasty warm and that will tell us what the difference is. I will do this tomorrow and sacrifice what I've tracked for my tank so far but is for the good of the forum, right? Certainly someone else has done a similar experiment.

 

Flash,

Currently my Trip A readout is the lifetime of the car (well, it had 8 miles on it when I got it, so that isn't included) and Trip B is reset every time I fill up, before I turn the car back on. You can key the accessories on, reset the tripmeter, then turn on the engine, and that's often what I do (or I do it right after turning the car on to pull out of the gas station). I record the reading for the prior tank on the back of each gas receipt and keep them in a drawer at home. Someday I'll go through the drawer and compile all my data, but in the meantime I have a pretty decent memory for most of it and I have the information in Trip A, at least. Though it seems to display incorrectly- the number of miles trims off the first digit, but the mpg still seems to be for the whole distance, not just the last 9000-odd miles of the 19000-odd miles on the car. actually it may have just changed to 20000- so I can check this again.

Also, I never idle. Idling is bad. Very, very bad. It's key and go, cold or not. If you don't believe me, listen to Canada. They've outlawed it. If you want data, don't idle your car and waste all that gas- the Canadian government has posted studies and I believe it has lots of data for you to swim through to your heart's content, if you just look for it online.

 

Leah - I'm not sure why people keep a Trip odo for the lifetime of the car because, like you note, it trims off the mileage once it hits 10,000 miles I think (Anahymbrid was doing this until it rolled over and then it was sort of pointless to use up a Trip meter for a single mpg readout). This is what the hand-calculations or our very own Mileage Database is for. I've written down the numbers from each fill-up (45 so far) and it is spot-on with the Mileage Database so I can then use Trip A for whatever I want and Trip B for whatever I want. Matt over on his daily blog uses a trip for each short trip I think though I just hand-write down these numbers and use that Trip meter for the whole day. Whatever works for you but you are "wasting" the use of that Trip meter if you are only going to use it for the mpg readout of the car, IMHO. No need to alter then since you don't idle. I'd still be interested to see what the difference is when the car idles for 10 minutes and has the Trip meter reset vs. the Trip meter that is reset prior to idling. We'll see who is brave to do this in the next week. I just filled up today but don't idle with the Block Heater so I'm sorta exempt.

 

I do not think the heat and defrost should effect your MPG very much. Just turn it off before you come to a stop so that your autostop kicks in. Then turn it back on when you start moving.