Not that I am asked for this, but just in case.

I came back yesterday from a round trip on I5 from Seattle to Tracy, CA. 810 miles one way plus whatever driving we had to do in addition. 2 passengers, myself, and associate, another 250lbs, plus about 70 lbs worth of - mostly his - luggage. Weather was cool going to Tracy, about 4 hrs with a/c on going back. Average speed 63mph per dash database. mostly cruising at 5mph above speed limit, short bursts if someone had to be passed. average outside temp was about 68-70, no rain.

it was a love/hate trip.

1. LOVE part. i absolutely enjoyed driving her on freeway. very stable, comfortable, good pickup in need. yes, she's still bumpy just like any mid-class shocks/suspension car, but overall, on a good pavement, very, very comfy. we took 3 mountain passes, cornering at high speeds and braking is absolutely up to my needs.

2. HATE part. this is not freeway vehicle. meaning - mpg wise. we left Seattle with rock solid 38 mpg average, and me being all fired up about how i'll come back with about 42. took me well over a month to build mpg from winter 37.5 to 38 driving here.
WE RETURNED WITH 37.5. on nav display, bars stayed steadily below 40mpg line. in-dash tank average showed 35.1, which i have never even seen on this car. powertrain performed beautifully otherwise, but no, she absolutely does not like hwy speeds. the very moment we'd get into slower traffic or simply drive around Tracy, mpg will climb up instantly, back to hwy speeds - drops down right away.

now i am back to inglorious task of restoring my 38mpg i was so proud of.

my mpg is based on long term data. i did not reset average mpg since october, so data are true and valid.

i know well enough this will be followed by "i have done 800 miles on a tank and averaged 55mpg on freeway" posts, as i have seen them. ppplease... unless you had a gene pushing your car - it is impossible. even without mountain passes and all that, and you living somewhere super flat - there's no way she will do 50mpg long haul, or get 800 miles on a tank AT FREEWAY SPEEDS. maybe long haul at 45mph, yes. not when speed limit is 70 and you are not dragging.

 

I drove from WV to Ohio, a trip of 240 miles, cruise set at either 65 & 70, (depending on the speed limit at the time). The outside temp was 85 and the nav system showed 42.5 mpg, not bad.

 

know the area, it's flat. worked in Indianapolis. question is - when was the last time your "average" mpg was reset on nav? as it makes all the difference in the world. i can drive out right now, reset that number, and will have very high mpg towards mid day. but if you reset it once, and then do not touch it ever since, it flattens out and really lowers itself.
before i left Seattle, i had 40.5 tank average and 38 solid on nav. last year, when i was resetting average mpg on nav after fueling, i had 42.5
apparently, it does all go down to if that number is reset or not.

 

A lot of the highway mileage depends on the speed. At 75 mph, I get right about 35 mpg. At 70, I get about 39 mpg. At 65, I get about 43. (Those numbers are from several trips between south florida and virginia -- 1000 miles each-way, with luggage.)

 

now this makes sense. well, like i said - not a freeway vehicle. actually, even they openly say hwy mpg is worse. and it's ok. but i should have known better than to listen to 50mpg stories. made an idiot of myself, when we took off and i bragged that "this car will get us to Tracy on one tank". THAT was embarrassing.

 

50 mpg is possible, I think. Just set the cruise control for 50 miles per hour. I have never had the patience to do that for any serious distance, though, so I cannot write from experience. I would also worry about being abused by less-patient drivers. Driving at 15 or 20 mph below speed limit is sometimes called "blocking traffic".

 

I reset the average mpg on the nav each time I fuel up. The 42.5 mpg on the trip to Ohio was a tank average.

 

just like i guessed. reset it once and don't touch again. let's talk in 6 mths.

 

i have no doubt it is. not at freeway speeds though. here in WA intentional slowing down normal traffic is a violation.

 

If you could somehow prevent the electrics from being used when you need to "regain" speed, I have no doubt your Prius' freeway MPG would improve substantially. On the freeway there is little chance for use of regenerative braking/coastdown so the ICE MUST be used, by default, to bring up the SOC once it gets close to being depleted.

On the freewway the electrics become nothing more or less than a SuperCharger, a pretty inefficient one, at that.