Fuel consumption due to the temperature drop

KR:

Om kort te zijn: ja!



As the temperature drops, the ICE has to run more in order to achieve proper temperature.

Additionally, there are typically higher electrical loads on the system: seat heaters, rear window & wing mirror defrosters, etc. This heightened electric load will cause the ICE to run more as well to keep the battery charged.

Finally, there is some evidence which states that the denser cold air provides more resistance. There is also a measurable decrease in fuel economy whilst driving in rain or snow.

 

Longer warm ups too (and i don't mean idling like my stupid neighbor)

 

Check your tyre pressures. I've gone from a 4.47 L/100km tank in July/August to 5.26 L/100km for the last one. That's measured as litres of fuel pumped, divided by distance on the odometer, not on the car's computer. I hadn't checked tyre pressures and noticed that the car was starting to feel reluctant to accelerate, and instead of getting 90+mpg (instantaneous) displayed on some sections (48-50mph, slightly downhill), the car would only show 60 or so.

Having re-inflated the tyres to 40psi front, 38psi rear, the car seems to just glide along and the high instantaneous mileage has returned.

 

We have all noticed a drop in our mpg ...... I am confident that is normal. But so have all the other vehicles (this is not a unique Prius trait). This week we rented a Mazda6 in Houston (it was cold and snowy). Mileage was right at 12 mpg .... far below the EPA figure.

Also, I am absolutely convinced the "winter blend" of gasoline is a real mpg killer.

 

That's a 23% hit... YES, probably normal... welcome to the 2010 Prius MPG winter plunge... frustrating, isn't it?

 

Excuse the crosspost but it's applicable here also...

http://priuschat.com/forums/gen-iii...n-only-getting-45-mpg-best-2.html#post1019686

 

You complain too much. lol

 

I agree this drop is about what I experienced. The important point is that you don't have to be frustrated. Go to the modifications section of this forum and search on grill block. I used pipe insulation and totally blocked my lower grill. Got my warm weather fuel economy back.

 

In really I don't understand why this is such a huge deal.

Scenario #1

If you drive for approx. 5,000 miles worth of "terrible" winter MPG (40mpg) you'll spend approx. $350 in fuel (125ga * $2.80).

If you drive for approx. 5,000 miles worth of "great" summer MPG (50mpg) you'll spend approx. $280 in fuel (100ga & $2.80).


The net result is: -$70 or $17.5/mo (4months)
.............................................................................................

Scenario #2

Now lets assume you are driving a conventional car of similar size to the Prius but somehow this car only takes half the hit a Prius does in cold temps. This car gets 30mpg in summer and 25mpg in harsh winter.

If you drive for approx. 5,000 miles worth of "terrible" winter MPG (25mpg) you'll spend approx. $466 (166ga * $2.80)

If you drive for approx. 5,000 miles worth of "terrible" winter MPG (30mpg) you'll spend approx. $560 (200ga * $2.80)

The net result of a 5MPG loss on a conventional car is: -$94 or $23.5/mo (4 months)
..............................................................................................

Scenario #3

Now lets assume you are driving a typical SUV or fullsize truck (non-diesel) assume this vehicle only takes half the hit the car in scenario #2 does in cold temps. This car gets 17.5mpg in summer and 15mpg in harsh winter.

If you drive for approx. 5,000 miles worth of "terrible" winter MPG (15mpg) you'll spend approx. $933 (333ga * $2.80)

If you drive for approx. 5,000 miles worth of "terrible" winter MPG (17.5mpg) you'll spend approx. $800 (285ga * $2.80)

The net result of a 2.5MPG loss on a SUV/Truck is: -$133 or $32.5/mo (4 months)
.................................................................................................

Do you see where this is going? Although your MPG number drop appears large, you are still paying less on average than you would in a regular car that took 1/2 the winter MPG hit.

 

I know what he was saying but it doesn't seem logical to me. I've always experienced MPG hits in the winter although I never tracked them like I do with the Prius. My post was to put things into perspective for those who are worried about a seemingly large MPG drop (number wise). In the end they are still ahead of the game economically.

 

I can imagine a conventional vehicle sees a minimal mpg drop because of following reasons.

A typical ICE efficiency is approx 30% and we lose 70% of gasoline energy.
The loss are mechanical, exhaust and cooling.
[ame="http://en.wikipedia.org/wiki/Engine_efficiency"]Engine efficiency - Wikipedia, the free encyclopedia[/ame]

The key here is differences of the cooling loss between a conventional vehicle and a hybrid.

We know a conventional vehicle engine always runs and always produces an excess heat. We sometimes hear a cooling fan is on to cool the engine temperature down even during idling time at stand still.
So, a conventional vehicle is always consuming fuel and is always producing excess heat, then the cooling loss is always existent.

OTOH, the engine on Prius is always trying to stop working on coasting and stand still, therefore the cooling loss is minimal and the engine is easily cooled down.
If the Prius driver needs cabin heat, the engine maybe has to run to create heat under these cool engine temperature condition.
This fuel, consumed for heating, does not provide motive power and it causes the mpg number down significantly.

Ken@Japan

 

I agree with the minimal loss compared to other vehicles. I am running around 5.4L/100km up from early fall results of 4.7L/100km. I live in a very hilly area, so I don't average as good as most Prius drivers.



iPhone ?

 

Certainly expected. We Prius owners watch gas consumption much more closely tan on conventional cars, so it's more noticeable. Winter gas, colder temps, and tire pressure (changes 1 psi per 9 degree F ambient change) which may of us have not adjusted since the summer, all add up.

 

I haven't noticed any real fuel consumption change in the last couple of cold weather weeks. The temperature has been falling down about 5-10C to 0-5C during the day and got some snow now. Not really below 0C yet, but should change this coming week (tomorrow -10C expected).

The major change in car behaviour is actually related to the ICE staying more often than normal. At the beginning I thought it was due to the temperature cooling down the engine too quickly (say during a stop&go traffic situation) but realised that it is mainly due to the heater. When I turn off the heater, the engine shuts down immediately, 9 out of 10 cases. In this way I have managed to keep fuel consumption practically constant around 4.8L/100km average on my commute. I need to try to use ECO mode to see if I get the same behaviour from the heater and the ICE doesn't stay on too often, while avoiding turning on/off the heater (distracting and annoying).

On a side note, I am also glad to read from SupaNativ that he gets a fuel consumption similar to mine, I thought that either my Prius was drinking too much or I was not driving it properly. Munich is also anything from flat and there are plenty of tunnels and flyovers in town. To get a straight, constant speed, flat stretch of road is almost impossible - even out of town. The whole area here is hilly.

 

One additional point to add from my side. I have just finished last weekend a 643.5km/400mi trip from Munich to Florence. The average trip temperature has been -8C/18F, with mins of -12C/9F and max of 1C/34F.

The average fuel consumption has been (as reported from the MFD) 6.1L/100km-38MPG at an average speed of 98km/h-61mph.

Is this bad, considering the temperatures and the winter tires? I don't think so.

Even including the 5% error of the MFD, I still land at 6.4L/100km-37MPG.

On German highway, I had a speed of 145-150km/h (90-95mph), in Italy 130-135km/h (81-84mph). In Austria the limit was 100km/h-62mph most of the way, with a good 50km/31mi section going on steep uphill through the Alps.

The highway from Munich to Florence goes through the Alps and then through the [ame="http://en.wikipedia.org/wiki/Appennini"]Apennine Mountains[/ame]. Check on Google Maps here for an idea of what the road looks like - anything but flat...

 

The fact that you are driving between 81 - 95 MPH certainly contributes your poor mileage. Prius's best MPG wil be between 25 and 50 MPH, although 60-65 MPH is not bad if you are able drive off of pure battery and stealth. Neutral started under 60 MPH equivocates to stealth. Driving in Brake downhill, when necessary ( down the Alps ) also produces good regeneration and stealth equivalents. ie: No fuel used. Hills and mountains can really never be blamed for poor mileage as for every hill (berg auf ) up, ther is an equal hill down ( berg runter ) Unless one RACES up and RACES down. The next factor for Winter Driving is the grill block, as mentioned previously, this does a excellent job. Don't be afraid of blocking the whole grill, it will not get too hot! BUT before I put my foot in my mouth, after installation, remember to check the engine, water temps to assure yourself it is working and everything is in order. Evan ( one of the moderators) feels confident that the grill block can even be left on in Summer. I have left it on in the 70's and 80.s F and noticed no harmful affects. Except continued quick warm ups and a improved 1st 5 minute bar. The Prius runs incredibly cool. There have been stories of Prius drivers racing up a big mountain grade and the car vitually quit ( in hot Calfornia Summer ) so the cooling system can be abused.Viel Gluck.