Lousy mileage due to heat wave?

I am seeing the exact same thing. My wife drives it, so don't know exact habits. I recently (@ 30k) changed from Valvoline to Kastrol (all 5w30 dino) & put a K&N engine air filter in. Also put on Pirelli P3000s, a bad tire for this car (max inflation "35psi" although I am running @ 39/37). Any similar changes on your end?

 

I can attest to poorer FE in higher temps. Recent tanks have been in the low 60's (calculated & MFD) but the one tank pumped when the temp was 97F showed 64.3mpg on the MFD but 50.36mpg calculated. The tank was filled in the morning when the temp was 77F. Could the temp increase have expanded the bladder enough to distort the calculation? The distance on this tank was 147 miles.

 

Hey, I live in your neighborhood and experienced the same weather. My mpg have been 53.5. Must be the AC or driving style. At the end of the day, I open all doors to get the heat out. Then I set the AC....dash and floor...at 68 degrees. Fan set at MED. I am comfortable and am happy with the MPG.

 

MPGs in mine in Dallas are reduced in the first several minutes of driving until the cabin and the battery cool down. This is normal. A Sunshade helps keep the interior from fading but the cabin will still get as hot (only more slowly) through the roof if parked in the Sun. Try to park where the shade will be when you come back to the car.

 

Actually no. The light coming through the glass heats the interior and the heat cannot escape back through the glass. This results in higher temperatures than ambient and much higher temps than would result from conduction through opaque areas of the car.

Here is a much better description

 

LOL....I was taking "Tourist" and "Snow Bird" to be the same....

 

For you northerners...

Tourist Season is summer. For the most part, kids and parents at Disney...
Snow Bird is winter. Old people, driving VERY slow or VERY fast. There is no in between.

Seriously, we love for both of them to visit our state. We only ask one thing: "Bring lots of money and spend all of it."

OK, enough of this nonsense,
Bob

 

Having lived in FL for over 10 years I am going to have to respectfully disagree with this statement. On days when I forget (OK, ok to lazy) to put my sun shade in the windshield I can certaintly feel the difference in temp in the car. If I step into the car during the middle of the day without the shade in place the heat of the car will take your breath away. When the shade is in place the car is relatively cool and the AC can bring it down to 80 fairly quickly. I've experienced this too many times to be convinced otherwise.

 

Uhh... you're right. My stupid mistake. A Sunshade does help, but you get a much better result if you can park the entire car in shade. Then the cabin will only heat up to the ambient air temp.

 

I am in the North East.
My experience is that cold weather, heating the cabin, and the change over to winter gasoline blend, hurts my MPG far more than hot weather, using AC, on summer blend.
In the heat of summer with AC set to 72 I consistantly get around 55mpg. As I did in the recent "heat wave" with outside temps above 90, I got 53mpg. In the winter with outside temps in the 30's I got around 44mpg.
By the way, the change over in gasoline blend is very noticeable, when the outside temps are about the same for weeks, but your mpg drops sharply, or rises sharply for no other noticeable reason.

 

We are currently experiencing 100f plus temperatures in California and I've noticed that the motive battery takes longer to charge, the soc drops rapidly even with the vehicle not moving, and often hangs at or near the bottom of the pink area. The car with 3200 miles on it never behaved like this before. The ice is operating more frequently and seems to be on more also at very low vehicle speeds. My air conditioner use is about the same as it is when the outside air is in the 70's, 80's, and 90's. Has dramatically lower efficiency of the hybrid system been documented in extremely high temperatures or is there perhaps a problem with it or the motive battery?

 

I'm guessing two things: 1) The AC is working harder, drawing the battery down and requiring more ICE-on time to recharge it; and 2) The hybrid battery is getting pretty warm. Follow the link in my previous post in this thread to a discussion of where I describe more ICE use, including the ICE lighting spontaneously at 26 MPH during a glide (something I've never experienced or seen described before or since) and sluggish performance in 104F temps, both seemingly caused by battery heating.

 

Over my life, I have read several magazine articles on tests between windows up, AC on versus windows all the way down, AC off. The consensus between the magazine articles has been consistent that if you are driving at highway speeds (65mph) there is virtually no difference between the two in mpg. So, pick whichever you feel more comfortable with. However, if you are driving at city speeds, then there isn't as much of an aerodynamic drag and so having the windows down would obviously be the better option.

Note: these magazine tests were using conventional ICE cars

*It's 99degrees here in SoCal today. On weekdays, when I have to wear dress pants and a collared shirt, I have to run the AC, but on weekends when I am just wearing shorts and a t-shirt, I never use the AC.

-I don't know if this is at all related, but as a kid, I used to build and race RC cars all the time. They never performed as well on HOT days compared to cooler days.

 

As you might mean to imply by mentioning the test vehicles, this does not hold true for the Prius unless the windows are only slightly cracked, as the chart in my earlier post suggests. In particular, auto AC set to 75F reduces fuel economy by 4% at 65 MPH (as compared to no AC with windows up), whereas all windows down reduces it by 16%. Even two windows only halfway down still reduces it by 8%.

 

I did not intend to dispute your chart. I was simply adding additional info. Obviously, since your tests are specific to the Prius, they will be more accurate for a Prius driver. I was simply adding additional knowledge that for an ICE at 64mph there was no difference. Since Prius operates only ICE at 65mph, I am assuming the difference is due to aerodynamics.

As for the batteries, does anyone here know about the resistance of batteries? I remember from physics class in college that as wires heat up, resistance increases and current decreases. HOWEVER, since the electric motor is encased with the transmission and engine on the Prius (maybe poor choice of words, but we all know what the diagram looks like), I would think the range of temp of the electric motor would be relatively consistent. Does anyone know if the cooling system (antifreeze) cools the electric motor as well?

More than anything though, from my experience with RC cars, I think it is the battery. Battery performance decreases significantly with temp. I do not know the electrical physics of batteries, but I know that empirically this is true (over many years, using many different batteries).

 

A car cover, which goes on the outside of your car is the best sun shade. If you normally go to lunch in someone else's car or eat at work, it's not much of an inconvenience to use a car cover. It keeps the light from entering your car in the first place. Second to that: on a really hot day, stop your wind shield wipers vertical and put your sunshade on the outside of your windshield. However, parking under a tree or canopy is the best, as zero sunlight is in contact with your vehicle (a car cover is still in contact with your car).

AN ADDITIONAL BENEFIT: the rubber, plastic, and paint on your car will still look new for many more years if you park it out of the sun or use a car cover. As a chemist, I can definitely tell you that UV sunlight will SIGNIFICANTLY speed up the deterioration of the materials that your car is made out of.

 

I have to keep reminding myself that on all of my other cars the AC was on or off. COLD air or OUTSIDE air.

With the Prius the air coming from the AC vents varies in temperature. As the cabin gets closer to the desired difference the AC doesn't work as hard and the air coming out of the vents is not as cold as it would be if the cabin were, say, 30 degrees or more warmer than the desired temperature.

Bob

 

No problem; I didn't interpret it that way. As I suggested, I figured you might have implied a difference between Prius and other cars by calling attention to the test being done on the latter.

 

I live in southern California and my mileage has been pretty consistent at around 48 mpg. But the mercury has been reaching 110 - 115 the past few day and my mileage had dropped to under 35 mpg. Knowing the inaccuracies of the fuel gauge, I always fill up somewhere between 350 and 400 miles since my last fill up. In this heat I took over 8 gallons and my gauge was reading over 1/2 full. Anybody else here in southern California experiencing similar issues.