Lowest MPG

Even in the summer, engine still cold and on ramp to expressway...under 5. Of course, the real lowest is 0, sitting in my driveway when the engine starts its warmup.

 

I've seen zero as well........barely breaking 40 MPG this tank. Could be due to the foot of snow I'm driving through and the temps in the teens.

 

with winter gas and cool temps in the morning and using the blockheater and driving for good economy I'm having a hard time keeping it above 54 MPG Imperial 5.2L per hundred km. Last 6 day's the temp has been about 3C about 36F 100% humidity (fog) which helps with the cooling. Keep the heater down to low on the fan and 20C. Once the ICE gets to 80C I turn the heat up to 24 and the fan to second speed. Trip home has no blockheater assist as there's no place at work to plug it in. Once over the big hill I'm back down to 3.5 L per hundred km. It's a struggle and I expect that this tank will have my mileage up, down for those south of the border. Still better than any thing I've had before, by a long shot.

 

I think 8 is the lowest I have seen other than sitting at idle. I have never seen a number lower than 8 while moving.

 

I don't let it idle on warmup. I get everything ready to go then start the car and as soon as I see "Ready" I put it in gear and go. I've done the same with every vehicle I've owned since 1967 and before (first licence in 1962) I guess I just didn't know any better. Winter summer spring and fall. I don't stand on it when it's cold but if it's burning gas it better be moving. Only time it idles is at stop lights and signs if there's traffic. I've been know to shut it off if I get to a traffic light just as it's turning red. Cheap, frugal, what ever but I don't burn more gas than I absolutely have to. Prius in S4 I don't shut off but if traffics bad and I'm not in S4 and it looks like a wait of more than half a minute I turn it off.

 

Evan,

It does seem to me logical that it would be somewhat more fuel efficient to warm the engine and exhaust system with the waste heat and the little bit of friction generated by driving rather than by burning fuel at idle just to generate waste heat to warm things. Also, much more waste heat is generated when the engine is under load rather than idling, so it warms up quite a bit faster going down the road as opposed to just sitting. Since the Prius was designed for shut downs and start ups it also seems in keeping with the intent of the car to hit the power button when the engine is cold and one will be idling for more than, say, 30 seconds. (It is a bit like the 'dark side' of an EV button, for those of us who don't have an EV button.)

One time when this might not be the case is if your block heater is still plugged in and the car is idling. Under those conditions the circulating heat sink of coolant might facilitate getting some more of that 400 watts of waste electrical heat into the engine per unit time.

Have you ever watched the mileage on your consumption screen go down during a cold idle?
If not, I suggest you try it. It is most informative if you have reset this screen recently--say a display of the average consumption over the last 5 miles or so--in your case a number probably in the mid 50's. Have your consumption screen on and do a cold morning start and idle without the block heater.

I find it alarming how quickly that cumulative mileage number will drop!

This actually suggests a way to quantify the effects of the block heater and other variables using the information provided by the car...

If you reset your consumption screen just before leaving work to go home, when you arrive home you will have an average MPG that is based upon a finite, relatively small number of data points. When you do the cold start with the block heater the next morning, as the car sits at idle you can time how fast that cumulative mileage drops. Time how long it takes to drop 1 MPG, for example. Reset the cumulative mileage to zero again before leaving work the next time. Assuming that you drive home the same way and that the drive time is equal, the average MPG that you obtain will be weighted with about the same number of data points. It should have the same 'relative mathematical mass', if you will. The next morning, do your cold idle without the block heater and see how long it takes the average MPG shown on the consumption screen to drop 1 MPG. If the block heater is effective, it should take a good bit longer. Trying it with the car idling and the block heater plugged in vs. idling and the BH unplugged could show relative changes as well.

Of course there are many variables that effect the initial thermal mass of the engine--ambient temperature, wind, how long the car as been sitting in those conditions, etc. The greater the thermal mass, the greater its 'resistance' to warming. The sum of those variables is reflected in the initial temperature of the block, however, so measuring the coolant temperature at startup reasonable way to assess the factor of varying thermal mass.

What do you think?

storm petrol

 

OK now that I am paying attention to this I get 2-4-5 m.p.g. I must be getting old my memory is going. Well as my professor in medicine would say " There is no good alternative to getting old"

 

Yesterday when it was -19 C in the morning drive to work, I saw 16 l/100km for the first block. It soon settled down to 5.5 l/100km, and once reasonably warmed up, 4.7 l/100km.

Parked at the mall yesterday when the car had a chance to cool off for 2 hours at -18 C, the first block was 25 l/100km. It never did get much better than 6 l/100km all the way back to my condo. Last year, under the same conditions without Mobil 1 0W-20, it was more like 35 and 8.

The Mobil 1 0W-20 is actually making a difference in cold driving, over the MFD tank average it's 5.2 vs 5.6 otherwise. Though it may also be related to the extra miles on the car now.

One thing I noticed yesterday at the mall when I returned to the car and powered up: with the Mobil 1 0W-20, the motor was quieter and smoother at -18 C. With the dealer 5W-30 last year it would buzz and vibrate a bit, now it's very smooth and quiet.

Just like Frank, I rarely idle gasoline motors to warm them up. Unless you're really putting your foot into it, it's almost always better to gently drive away. The motor warms up much faster and less blowby is created.

Diesel motors are another matter. Most diesels are hard to start in winter unless plugged in, and there is usually a lot of blowby if you try to work them cold.

 

Evan my first traffic light is 9 blocks from home and it's a right turn and here you can make a right turn after a stop so I just wait for a break in traffic and go, the next light is a loading coil light so I watch the pedestrian walk light and if on I don't start to slow, it's a slight down grade so I can just coast if it looks like it's going to change, the next light is a "long" light and I've timed it at 2 1/2 minutes, if I get caught at that one I will shut down, if I just let it idle the temp rises 1 maybe 2 degrees C, if I shut down it never drops more than 1 degree C so burning gas for 2 1/2 minutes to generate 2 degrees max is a waste IMHO. The run to the next light 5 blocks will have me in S4 most days unless it's really cold and rainy. If I'm not in S4 then I shut down again unless I'm at 68-69C as it'll normally rise to 70 and if I can get the last 6 seconds to put it in S4 I'm from there on I'm on a 1200' climb for the next 35 blocks so it's going to burn gas no matter what I do. My life time average mileage with a Classic is 45.23 US mpg so there must be some method to my madness. :blink:

 

for thoes in cold weather, have you considered putting a cold front on the engine side, to assist in warm up. Since once we get to S4 we shut down at stop, we wont need to worry about over heating in traffic. Seems to me that we want to get to S4 as soon as possible.

 

done you can read my "butt ugly" post in the block heater thread.

 

Climbing a steep unpaved road, avoiding pointly rocks at about 3 mph yields about 3 mpg. Prius is *quite* unhappy in this operating regime. ICE cannot get to its power at low RPM and the motors are pissed off about something but I was not instrumented at the time, so several options remain. Hybrid vehicles intended for such operation should definitely have a low gearing available.

 

instaneous, will definitely be zero. the lowest 5 minute reading... well had on at about just under 5 mpg. mostly because i went out, ice all over car, started it cranked defroster, scrape, get in car, drive a block, realize forgot cellphone, return to house, get out leave car running go in, get cellphone, come back out, start driving, few seconds later, first bar pops up, and its definitely below 5 mpg. probably 3 or so. i have also had zero readings...several times... happens all the time if car is running and you are not...guess i need to reduce fast food habit or go to place less popular...

 

On a similar note what is your lowest average mpg when starting out from a dead stop on the flat for the first 0-20 mph. If conditions are right I can take off on the electric but at about 8-10 mph the ice cuts in. I generally get some flow from the battery and it is very hard for me to achieve dead banding (no flow too or from the battery) from a stop. What about others?

 

im same as you Henry. unless i force EV mode, all but the slowest of acceleration will still kick the ICE on so i just accelerate normally to speed and then hit CC and it will goes into EV if going slow enough and the ICE is warmed up at least a little.

 

Well i'm sure we've all floored it sometime and gotten below 5 instantaneous mpg, or maybe between 5-10 if the ICE is warmed up. The lowest I've actually seen is 3.0, but the time when I actually went all the way to floor (didn't notice a truck right next to me on a no shoulder merge, oops) I wasn't exactly paying attention to the screen. :lol:

For my lowest 5 minute average mpg I've ever gotten, it would be somewhere in the teens for me, if I start off before the ICE warms up.