Folks,

I flew into Atlanta a few days ago and was renting a compact from Enterprise and had a 400+ mile trip to take into the boonies in SC. They were out of cars and offered a minivan, SUV, or the Prius as an alternative. I took the Prius, of course.

My initial impressions were:

1) Nice car overall, and a little but more solid feeling than the HCH.
2) Cool - key fob and power button
3) Much more hybrid.

Once driving:

1) More quiet
2) Radio sucks
3) Gets much better mileage and the system in more advanced.
4) Brakes and tires are much better -- the HCH gets jumpy when you need good breaking.
5) Seeing out the back takes some getting used to, but it is not bad.
5) Drove many miles on highway and rural roads -- getting great gas mileage -- the computer average said 51.9 and we were at high speeds.

Then I refuel and return it and did the calculations.

When I calculated the actual mileage with the Prius it was only 40.99 (418.4 for 10.221 gal)?

The prius computer was way off -- I think my HCH would have done around 43 under the conditions.

Dobe

 

Is your observation from one tank filling only? One tank of gas has a lot of room for error -- especially when it comes from a rental agency. Several consecutive tank fills, taken to an average, will provide a proper mileage rating.

BTW, I happen to know that my HCH-II's trip meter fuel efficiency is estimating about 4% poorer than what it really is.

 

How does a tank of gas have a lot of room for error? I have always been told it is the most accurate way.

 

Interesting comparison between the HCH and Prius. I have two observations as to why the refuel mpg was off.

- Often the previous renter refuels the car prior to arriving at the rental agency. That can easily add 10 or 20 miles to the tank.

- The Prius has bladder in the fuel tank, and that makes it notoriously difficult to fill it "full" to the same level every time. Colder temperatures can take a gallon off "full" due to the bladder getting stiff.

 

Yes, tracking your fuelings is the best way, but the math works on the assumption that the tank has a maximum size. You will never get it completely full, but you can fill it consistently over time, providing your maximum. Here are some contributors to mis-readings:

• Tank appears full from the dealership or rental agency, but some of it was burned during transportation
• Fuel can settle and the tank can take in more fuel after a bit of time (especially true of diesel)
• Different pumps may have different pressure click-off points
• Temperature differences
• Car is tilted during fueling, offering more or less tank access

Any ways, all of the above doesn't matter when you have an average of several fillings to remove the difference between full and full-full.

That's all I'm saying. Picking up a rental and refilling just once won't give an accurate result. If anything, it will make the fuel efficiency appear worse than it really is.

 

Then what is the proper way to calculate your MPG by hand?
Can you give an example?

 

 

The only accurate way (using US measures) is:
Total of all miles driven divided by total of all fuel used in Gallons.

I think the Canadian System uses:
Total liters of fuel used divided by the total kilometers driven, so the two systems are inverse to each other.

I added an aircraft type fuel flow transducer to my TCH and over about 6K miles of driving I have seen it agree with the "hand" calculation above within less than 1%. However, the Toyota computer in my particular car usually is a little more optimistic and reports about .8 to 1.2 MPG better that the hand calculation or the FF system reports. I suspect that individual cars may vary considerably as I rented a Prius down in Texas that under-reported its FE over several tanks.

 

Interesting post--I've always been interested to see how "the other half lives" and drive a Prius for a little while. Your experience reminds me though, that if I ever get the chance, I should hit the gas station to top off as soon as I drive it off the lot.

 

My wife rented one while on a trip to San Diego. She normally drives a 4Runner but will take Little PutPut for trips up to Ft. Worth so she is familiar with the HCHII.
Oddly, she didn't like it. Her impression was that it was sluggish. She didn't like the ergonomics and starting it was convoluted. I really thought she'd like it better due to the numbers for acceleration (she can get 36 mpg in the HCHII) and the ability to be full electric at times. I still haven't driven one; but after her comments I am pretty ok with that.

I'm not bashing although it kinda looks like it. I just found it interesting that on paper the Prius looks to be a sportier car while real world impressions are different.