Influence of speed, temperature, and weight on MPG

There is an entire thread about grill blocking strategy, I would look there. I haven't read it as it doesn't get cold enough down here to justify it, I didn't think, and my wife drives the car more than I do, making it impractical as she would not monitor temp.
I would have thought that at steady high speeds where the ICE was always on and at relatively high power, that heat output would be way more than enough to keep the engine at 190f, even if you were running the interior heater at full blast. I wouldn't think that grill blocking would be necessary in such a situation, but without some form of coolant temp gauge, it's just speculation.
I would not block anything without a way to monitor temp, heck I don't like the fact that I can't monitor oil pressure, that really bugs me, but I guess I'll just have to get over it as I don't think I'l add an oil PSI gauge.

 

Here it is, I think I will spend the next few minutes reading it http://priuschat.com/forums/gen-iii...62556-2010-prius-grill-blocking-strategy.html

 

Big time. The higher I have my temp set, the longer my ICE runs even @ stops. Big hit. I just leave my set @ 66 now.

 

During Summer and during highway driving now, it runs between 190 and 195 or so. It's in town driving around at 45 MPH or less that the temp seems to not reach 190 or even near that.

 

The aerodynamic drag is proportional to air density and the velocity squared. Using the Wiki table:

	Column 1	Column 2	Column 3	Column 4	Column 5
0	C	F	density	drag	MPG/ (drag**2)
1	-25	-13	1.423	116%	38.5
2	-20	-4	1.395	114%	40.1
3	-15	5	1.368	112%	41.7
4	-10	14	1.342	110%	43.3
5	-5	23	1.317	108%	45.0
6	0	32	1.292	105%	46.7
7	5	41	1.269	104%	48.5
8	10	50	1.247	102%	50.2
9	15	59	1.225	100%	52.0
10	20	68	1.204	98%	53.8
11	25	77	1.184	97%	55.7
12	30	86	1.164	95%	57.6
13	35	95	1.146	94%	59.4

Hope this helps.

Bob Wilson

 

Good data and good reporting. It's very well done.

 

Indy,

Did you also record the road condition? Any of those days were raining? Snowing?

 

Looks like the EPA needs to expand their fuel economy tests based on winter/summer driving.

 

Great stuff, Indyking!

Have you done a regression analysis (is that the right name, statisticians????) to figure out the contribution of each measured factor (particularly speed and air temp) to MPG variability?

Statisticians, given the amount/type of data presented here, can he do what I'm suggesting?

BTW, one thing I find is that avg mph for a "trip" (usually a gas tank, for me) is not a good indicator of actual gas-sucking speed--i.e., a trip with a lot of 75 mph cruising and a lot of sitting around in traffic may show up with a lower average mph than a trip with a lot of 65 mph cruising--even though MPG loss from excessive speed will be greater in the trip with 75 cruising.
The way Indyking describes his trips, this shouldn't be a problem for his data--but it may be a problem for the rest of us trying to reproduce his results.

 

Wind speed and velocity has a major effect on FE for all vehicles.
The more aerodynamic the vehicle, the greater the effect. Wind
direction becomes important as little as +/- 15 deg off the vehicle
centerline. The result is that the airstream does not wholly flow over
the body from front to rear. Some of the air, increasing as the off-
center angle increases, "spills" over the side of the vehicle, causing
major turbulence --> increased drag --> decreased FE/MPGs.

There have been a number of discussions on this matter in the past.
Here are three samples: (Granted, these are Gen II based, but the
effect noted is universal.)

http://priuschat.com/forums/gen-ii-prius-fuel-economy/44843-wind-how-much-affect.html

http://priuschat.com/forums/gen-ii-prius-fuel-economy/39537-weather-conditions-effect-mpg.html

http://priuschat.com/forums/gen-ii-prius-main-forum/15448-wind-effect-prius.html

A trip between Indiana and Michigan would mostly be perpendicular
to the westerly prevailing winds. Even small wind velocities could
result in non-centerline air flow over the car and significant FE/MPG
hits. Could it be that in the Midwest, cold temps are typically
connected with MPG robbing winds from the west? :noidea:

As noted in the second thread, there is a Prius MPG Simulator here:
Prius Palm Mileage Simulator . Keeping all other variables constant
you can fiddle with wind velocity and direction and see their
insidious effect.

 

Re: Influence of all kinds of stuff on MPG

From my point of view as a driver keenly interested in all things
effecting FE/MPGs, this exercise is interesting. But, I wonder if there is
any way to tease apart the many factors known to influence FE/MPGs
in an exercise conducted in an open, uncontrolled experimental
environment looking to isolate the contribution of OAT alone.

It is a widely accepted fact that all else being equal, the Prius gets
best FE/MPGs at outside air temperatures (OAT) roughly between 55
and 75 degF. As OATs go higher, but more significantly for this
exercise lower, FE/MPGs vary in a non linear way. This was
acknowledged in the OP: "I'm convinced that temperature is the major
factor considering the speed range I drove so far."

It is also known that OAT is not the only factor that influences
FE/MPGs. Other factors so far identified in this exercise include:
* terrain
* velocity
* vehicle load
* rain -- presumably standing water on the road surface
* Use of heater to warm the passenger space
* ICE block temperatures -- use/nonuse of grill blocking
* tire pressure (constant? TP drops ~1psi each 10 degF drop in OAT)
* traffic levels
* Consistency of fuel fill-up volumes

Other factors mentioned in the exercise but not recorded/considered
significant include:
* humidity
*Atmospheric pressure as as factor in increased "drag"
* wind velocity and direction -- more telling, the angle of departure
from the vehicle centerline

Other known factors not mentioned to date include:
* windshield and hatch glass defrosting
* "winter gas"
* possible aerodynamic contribution of grill blocking
* "Human factor"
* use of Cruise Control (to reduce the human factor")

Other indirect factor which may influence FE/MPG :
* time trips were made --driver attention when driving in darkness
vs. daylight

This is from another forum, it illustrates the many factors that
contribute to cold weather MPG reduction:

Anyway,at 20-degrees F, compared to SAE's standard 60-degrees,
on a day with standard barometric pressure, the air density would
be over 8% higher, and your drag would consequently be 8% higher.
At your colder temps, it's even worse.
Factor in that your tires are "cold" at 70-degrees F, and that even
after 22-miles of continuous driving, when you reach your warmed-up
equilibrium temp for all lubes and coolant, those temps are still less
than during warmer weather.
Thick oil, tranny fluid, gear oil, coolant, hard tire rubber, and denser
air, all conspiring to kick your butt at the gas pump.


Is it really possible that through statistical manipulation the
contribution of all the above factors can be identified, isolated, and
removed from the effect of OAT alone?