Getting horrible fuel economy

cold weather destroys mileage.

 

You have indeed found the Achilles Heel of the Prius!!!

Even here in Sunny Los Angeles, when it gets cool, (I won't offend anyone who has to deal with -35 actual by saying cold) temps in the morning 40's, my milage took a hit!!!

Now that we are back to 80's in day and 60 at night it has returned to "Normal"

Next week winter returns, OK just a little rain, and 50's. However I see another milage hit coming my way!!

73's de Pat KK6PD

 

jamesrm,

You might want to check your oil level.

Posters have reported that "overfilling" up to the High mark on the dipstick,
the full recommended 3.9 qts IIRC, can result in lowered FE/MPGs.

Likewise posters say that refilling the oil to midway between the High and Low
marks on the dipstick, about 3.5 qts, is as "full" as the crankcase needs to be.

 

Cold weather is not just the Achilles heel of the Prius, it's the Achilles heel of all internal combustion powered cars. Winter mileage drops in all normal cars, but it's easier to see in the Prius due to higher mileage and better instrumentation.

Tom

 

I'm too scared to check my fuel economy since winter came. I used to get 5.2 L/100 KM (about 45mpg) but I've noticed that you have to drive the car around for quite a while before it will stop idling at red lights when its colder then -20 C.

 

Do you mean a block heater? Glow plugs are used to start diesel engines.

Tom

 

Batteries don't like cold weather either. And since the Prius doesn't turn off the ICE until it and the exhaust are warm, temperatures have a bigger effect on the Prius than on cars that always run the ICE anyway, cold or warm.

 

I've had my car for three years and have driven it through 2 prior winters- it's an '04 Prius and has 67,000 miles on it- and a few months ago my car suddenly started getting 20-25 mpg when before it has always gotten about 40-45 mpg. I've taken it to the Toyota dealership several times and have been told that nothing is wrong with my car and that it is just the cold weather, but I find it strange that this did not happen the last two winters and also a little frustrating since no one can give me a good explanation.

 

A tough hit for all of us - but worth giving some thought on qbee2's comments that it's, '...easier to see in the Prius due to higher mileage'.

Your approximate drop from 450 miles per (say) 9 gallon tank to 350 miles mean that you are roughly now using just over 0.5 gallon more gas for every 100 miles (50 mpg dropping to 39 mpg).

However, if a 'normal' car dropped its mileage from 30 mpg to 20 mpg, this is equivalent increasing its gas consumption by 1.67 gallons for every 100 miles - more than three times more gas used compared to you, even though both experience around a 10 mpg drop.

Perhaps our hit is not as bad as for many others!

(More on this concept on the fourth 'sticky' of this forum!)

 

I wish I did so well.

 

What is your outdoor temps right now?
How long are your trips?
Do you use the heat?
Are you grill blocking?
Have you checked your tire pressures? What about engine oil level? Also check your cabin air filter.

 

The OP mentioned that he just put on new tires. He didn't say what kind. Mileage in the Prius is very tire-type sensitive. I agree with the other comments about how cold weather affects mileage in a seriously detrimental way also, as do short trips, but tires are also sometimes a factor.

 

Cold weather factors:
1. Cold ICE and coolant require the ICE to operate just to keep the engine warm.
2. Many humans find the need for some heat as well...this means the ICE runs more and hurts mileage. (Defrost will hurt it even more.)
3. The battery is cold and part of the cold weather idle cycle seems to revolve around charging the battery to warm it initially. (This is my synthesis of some info I've read recently about battery response to temperature. If it is incorrect hopefully a guru will correct me.)
4. The gas tank bladder shrinks in cold weather, reducing the amount of gas that can be added and therefore the range between fills. By my calcs this can be up to 15% in my locale. This doesn't impact real mileage, but does result in annoyingly short range, especially when combined with other factors above. This is likely to be most obvious on the first pip and perhaps the bottom. I've noticed a reduction on the top pip, but that might be specific to my car.
5. Standing snow/water etc. will also reduce mileage (rolling resistance increases.)
6. Cold, dense air (and higher pressure in the cold fronts to a lesser degree) will also increase aerodynamic drag at highway speeds.

 

What are the pressures in the tires on a cold morning, before you drive anywhere?

 

Don't feel so bad, my 2007 is getting 38.7 right now. I even have an engine block heater! But, to the Prius' defense, I live 3.3 miles from work, I do not have the grill blocked, and I have been driving back and forth to Children Hospital (sometimes twice a day) for the last 22 days and it's only 6 blocks away. Those 3 things will kill mileage.

And no, I'm not going to walk to the hospital if it's dark. I have to walk through the 'hood.

 

I have an '06 Prius. I used to get 55/mpg until I had a new set of tires put on at 40k miles. Since then I have been getting around 45/mpg. Since the weather has gotten cold, I've been getting anywhere from 36 to 42/mpg. So.............it seems tires and weather have something to do with it.

 

Had to LOL at that. I live in the central OH area myself. Even when I was a child and came to that hospital for visits to my younger brother - it was a rough neighborhood. Some things never change. So no, I don't blame you one bit for not walking!

 

IMHO no really good reason for that kind of drop. In Chicago, I've averaged 39 - 42 mpg over the last two weeks and the temps have ranged from -15 to 30 (Fahrenheit). Regarding what I do, i'll answer Bob64's questions below.

1. It is 35 miles to work. Then I drive for work anywhere from 1 - 70 miles away.
2. I keep it on AC / Auto set to 70 degrees.... Comfy
3. Definitely grille block below 40 degrees. (Never been to socal so I don't know how cold it is).
3. Tires at 44/42. Oil never above 3/4 and never below 1/2 full. Filter change spring, summer, and fall.

Once the temp is consistently above 50 and below 80, i'll average 52 - 54 then once it's above 80, the A/C will limit my mileage to 48 - 50. Comfy again.

I would also recommend checking the MAF as it can impair mileage. Have you ever checked your plugs? I replaced mine at 60k but they didn't look that bad.

EDIT: Sorry to the OP as I see you are in TN rather than socal. I was thinking back to the previous thread that I was reading.