Very low MPG across two states (38-40 MPG)

I suppose there are many ways to look at this issue. In the end, it's a no-brainer, the faster you drive the more gas you're going to use. Period. Can't fight physics/chemistry. Just the way it is.

 

That's pretty low I do not see what is going on. Usually I do not see huge MPG hit with roof rack until I am carrying something up top. We do not get 500 mi/tank unless we are doing 100% highway in which case our record is about 485 miles ...we were able to do that this summer a couple times.

 

Bingo! Now you tell us!

I've never seen the HSI "CONS." number near 50 for a whole tank, either. It practically always lands in the 56-64 range, winter or summer, local or long-distance travel. (Actual mpg is 95% of what it claims.)

 

15 miles commute should get you about 45-50 MPG. Something is wrong. We averaged 47 MPG when my wife was commuting 12 miles to work (24 mi round trip). We are lower MPG now with all local driving.

Have Toyota take a look? Rent or get a loaner Prius to test another vehicle on your commute? Check to make sure actual MPG (by hand calc of gallons pumped) is similar to display (display usually over-optimistic).

 

Have you ever driven it without the rails? If not, I would remove them for a few tanks (if you won't be needing them) and see what happens. If its still/has been low without them, it might be worth it to test drive another from the dealer on a loop and drive your car on the same loop to see if there's a significant difference.

 

I do not have the wind deflector, but my bars by themselves do not seem to hurt MPG too much. My rack comes off easily so I do not use them often. Keep in mind the wind deflector could be adding quite a lot of drag and frontal surface area. I definitely see -10MPG with my box on top, and your wind deflector could conceivably add as much surface area as my box.

 

First post photos, front, side, and top. Let us see what you have.

Bob Wilson

 

You need to do a tuff test. Use blue masking tape that pulls off without leaving a sticky spot. Use gift wrapping tape 3 inch, long, 1/4 inch, along the top about every foot or so, at least a foot from side all the way to rear spoiler. Include the rear glass. Then drive at least 50 mph and have a friend make some MPEGs or rig a camera to take photos.

You will see a huge amount of energy wasting, reverse flow turbulence that is drag. Without the air.dam and rack, the air would follow the body taper and actually provide a little push, reducing the drag.


I understand the desire for more cargo. First choice is a trailer hitch and platform. Stacked no higher than rear spoiler, drag free. As for roof racks, the ones that go front to back are the next best and alleviate the need for an air dam when not loaded.

Good luck!

Bob Wilson

 

No, I didn't misread or misunderstand at all. I was trying to make the point that you're getting lousy mileage for a Prius. Do Bob's steady-speed test without the aerodynamic impediments, report the results, and then we'll know whether you actually have a car problem, or only unreasonable expectations.

That deflector looks to me like might be angled too high. You'd have to test to find the optimum angle.

 

Many years ago, I tested vortex generators on our 2003 Prius to see if they might improve highway mileage:


Before vortex generators a lot of evidence of flow reversal.

With the vortex generators:

Now the flow is attached with some separation on the passenger side but not as severe. But I did not stop here.

I ran my standard, high-speed benchmarks and could not find evidence of a significant MPG improvement. Not enough to justify the maintenance hassle of dealing with car wash systems.

A 'blown' plexiglass cover could be formed that would keep the flow attacked down to the spoiler. But then we got a 2010 Prius and it is our cross-country car. The 2003 Prius is used for city driving.

Bob Wilson

 

We took a trip fro Minnesota to Yellowstone this summer.

South Dakota recently changed it's freeway limit to 80MPH. Wyoming also has an 80MPH limit. Add that limit to any headwind and *any* car/truck will have difficulty getting decent mileage. Needless to say, I did notice a drop while going through those states.

The funny thing is...hardly *anyone* was going 80...much less going over. I'd estimate that, on average, trucks were going in the low 70s and most cars were going 75 or so at the most. I frankly didn't expect that at all.

 

In other words, the same speeds they go on Interstates with 65 or 70 mph limits, proving most people ignore the limit signs, whatever they say.

 

Luv Yellowstone...last time we went we had a room in Old Faithful lodge directly with Old Faithful out the window.