Possible to increase interstate mpg? Scangauge?

Certainly 15 inch wheel could gain 3 MPG, but the payback will be quite a few miles, at least wait until you need new tires.
You are in FL so grill blocking will not be wise. A/C near 75?
I run headlights as I value safety over MPG, but I am not on a freeway.
I would guess the scangauge would be more helpful at speeds under 45 or on hills.
Make sure your next set of tires are Low Rolling Resistance.
Clean cars are more fuel efficient than dirty cars, any brackets you can remove? bike carriers, etc. trim dangling? underneath smooth?
Check your 12 volt battery, consider changing your ATF next service.
I carry a lot
of tools and supplies with me, weight hurts MPG, have cleaned the inside?

 

FWIW, Motortrend measured the current Jetta TDI at ~38mpg at a constant 75mph, not including the penalties for higher carbon content/output and cost.

40 MPG Compact Sedan Comparison - Chevy Cruze Eco vs. Ford Focus SFE vs. Honda Civic HF vs. Hyundai Elantra GLS vs. Mazda3 vs. VW Jetta TDI - Motor Trend

Maybe someone will chime in with some more ideas, but honestly I don't think you are going to do too much better at that speed. You are mostly up against the physics of air resistance, the effect of which increases rapidly at higher speeds. Most of the tricks people do relate to optimizing efficiency when stopping and going, reducing the impact of the warmup cycle, etc, none of which are really going to impact your long high speed drive that much.

Things you could try:
- Increase tire pressure further, some people run up to 50psi I believe. You still want the fronts a few psi higher than the rears for safe handling.
- Try partial grill blocking if your driving temps are routinely 50s or below.
- Try smaller wheels, could reduce unsprung weight and could also reduce your total drag area slightly. Wind resistance is directly proportional to coefficient of drag * frontal area. Probably not enough to notice for many, but maybe in your extreme case it could show up.
- See if there are tire choices available with better rolling resistance. There are a number of threads on the topic around the various PC forums.
- Use cruise control if you aren't already.
- If you have any inclines to play with try allowing some speed to slowly bleed off on inclines, recover speed on down slopes.
- Try drafting (at safe distance) different types of vehicles. Semi's aren't always the best choice due to the high deck height and turbulence generated by the open undercarriage.
- Try letting your foot "float" on the gas pedal as much as possible. There is usually a small range of pedal positions that will maintain the same speed, so you can sometimes get a little better mpg without losing any speed. A scangauge might be of some help there, don't have one so don't know. May be tough to beat the cruise control though.
- If there is traffic, "read the road." Watch traffic further down the road to avoid braking / accelerating any more frequently / quickly than you have to. IE leave a buffer between you and other vehicles. Use it to "soak up" the speed changes of vehicles ahead. If you think you are going to have to slow down, start coasting or gradually bleeding off speed as early as you can.

Bear in mind that anything you do that requires continuous active engagement can make the drive much more tiring, which for the amount of time you're spending in the car every day could be a safety concern in of itself. If its fun, and helps keep you occupied great. But if its tiring you out, you may be better off just setting the cruise, cranking the tunes, and being ok with just driving one of the most efficient vehicles you could have chosen.

Or you could move

Best of luck,
Rob

 

I don't think a scangauge would help much. There is the super highway mode (described here on CleanMPG) that is much easier to achieve using a scangauge, but you would have to drop your speed. Another way it might be useful is to let you know if a grille block is making it too hot.
On the highway, modding the aerodynamics makes the biggest difference. It can look silly, but that will be your best bang for your buck if you do it yourself. The AeroCivic is an example of what going all out can do.

4 hours of commuting? I'd be looking at moving closer or finding a closer job over improving mileage.

 

2 possibly 3 things are keeping you from the 50 mpg goal. One is speed (you would probably have to cut it to 65mph, Second are the 17 in wheels and tires, 15 in with Michelin A/s tires will help, and third possibly cruise control (you will do better not using it.) So it's your choice, if it were me in your shoes I'd live with it as it is and stop worrying about it.

 

You could try a grill cover to help with aerodynamics but a Scanguage would be absolutely mandatory to monitor temperatures there in Florida.

 

If the Scangauge is too expensive, there's an app for Android called Torque Pro that costs $4.95 US. Then get an ELM327 Bluetooth OBDII adapter from Amazon/E-Bay for under $20 US. They mostly work the same and a lot of members here like the UI of Torque much more than the Scangauge.

 

If you're considering the SG-E, take a look at the Ultragauge. The biggest difference in a Prius is that it doesn't have anything like X-Guages (but neither does the SG-E). It'll tell the temperature just good as the Scangauge, and be able to show more gauges at the same time.

 

Just a note to the relative newcomers, ScanGauge-II gets mentioned so often because many of us oldtimers cut our teeth on it, and still use it despite its ancient user interface.

But there are many other products, some newer and with nicer user interfaces, that perform the same monitoring functions and code reading functions. Some won't have their own equivalent of X-gauges, but will still be quite effective for many users. With the proliferation of smartphones, many will find phone apps such as Torque more cost effective and possibly more useful.

But many of us still say 'ScanGauge' even though any engine monitor will do just fine.

 

We've got pretty much the same vehicle, Canadian touring model with the 17" wheels (with Michelin Pilots. They're not billed as LRR, but still, seem decent). My main advice would be to find some way to slow down. Stay to the right, get behind a truck (not drafting, just pacing).

There's graphs on the 'net that tell the story: as your speed goes up your mpg goes down, and that drop accelerates as speed climbs.

Also, I've found the cruise to be very good at efficiency, this is watching the instant mpg numbers on a ScanGuage.

 

The Scanguage can help staying in the sweet spots up and down grades and in the speed range below 60. On a flat road at 65 mph or above I doubt you will see all that much benefit from it since cruise control does a reasonable job in steady state conditions and your ICE will be running at a steady RPM.

Speed and Air conditioning are where you are taking big mpg hits.

No grill block in Florida.

 

If the Prius is the second loudest car you've ever driven on the highway, you might need to consider getting some tires that are less noisy though at the possible expense of worse fuel economy.

 

I can't imagine that changing wheel sizes would automatically change your fuel efficiency.
It depends more on the tire composition than the size.

Don't these models have a "5 minute" fuel efficiency display......or is that new for '12 or '13 ??
My '13 C has that and it seems to be very good at showing your "instant" fuel usage.......similar to what you could see with a scangauge.

 

All 2010 Prii and newer have a 5 minute display. Can't speak for the c or the v though.

And yes, increasing wheel size lowers your fuel economy.

 

Larger wheels are generally heavier. Also, the OEM 17" wheels come with wider tires than the 15" (at least on the '13). That can cost you a couple MPG in a Prius.

 

As a general statement, that is not true.

As the post above states, it might be true for a given combination of wheels and tires, like the OEM
offerings for the Prius, but it certainly is not always true.

 

Check. Thank you.

 

Do what you can to reduce your average speed. If your AVERAGE is 75mph you'll going a lot faster than that.

Inflate the tires to max sidewall pressure. If they are not the original tires they may not be Low Rolling Resistance. The difference in fuel economy between LRR & non-LRR over the lifetime can pay for the tires.

My grill stays blocked all year--even on my cross country trips. On some trips I did pull the upper pieces at rest stops when I noticed temps rising at rest.

Hook something up to monitor engine coolant and inverter temps. The ScanGauge (yeah, I'm a geezer, too) has other uses as well but this is a start.

Keep the cabin temp as high as you can & on auto.

Put a sunshade in the windshield when parked.

A weak 12v battery will reduce fuel economy because the engine will run more trying to charge the battery.

Run in Eco mode. It remaps the throttle response and climate control.

The avionics certainly make the longer trips easier. I feel I can do a better job than the RCC but really can't prove it. On flat terrain in steady traffic it should be a wash. Either way find a steady speed. Speeding up to slow down is a waste.

Given the speed, honestly, I'd expect 45-46mpg. I get 48-49mpg & can goose it to 50 but I'm down at the speed limit.

You've got a great car for the job. Enjoy.