Cruise Control VS. My Size Thirteen

[davidiiiii]

Hello G IIIer's:

I've been a professional lurker for about 6 months now. I've slapped around the idea of getting a Prius V or a Golf TDI for so long now. I've decided to go with Prius because of the massive difference in desiel prices around here, and the fact I've seen so many huge black spots around the new model Jetta TDI's bumpers driving around here (clean desiel my !$%...)

I drive 40k - 50k miles a year with about 75% being highway. Just purchased the Prius V last weekend, and although I love trying to maximize my mileage by using the HSI as a guide, it's honestly starting to stress me out! With all of the craziness in other drivers I would like to honestly just focus on the surroundings around me using cruise control, rather than playing the force the engine off and glide game. I truly believe I can obtain better MPG than the cruise control under 45 MPG by forcing the engine off when it doesn't need to be on, but how does it do at highway speeds? Whenever I use cruise now on the highway, it seems to keep the HSI much higher than I normally do...however that's because when I'm controlling the car, i'm free ballin around in Glide Mode as much as possible, constantly losing momentum that I later have gain (possibly being counter productive).

Seeing how I just purchased my car, I haven't really had enough time to do this study myself, and the temps have been fluctuating from the 50's to 20's daily. I'd appreciate any info and statistics that you G IIIer's have come up with so far. MFD indicated at 52.1 mpg to date

[brick]

Well, in my 2G the only problem with cruise control is hills. It tries like mad to maintain exactly my set speed so the engine revs up and out of its most efficient band. (Traffic permitting I prefer to bleed off a small amount of speed on the way up, occasionally accelerating just a bit before I get there to compensate.)

If anything I think that the 3G should have less of a problem in this regard. You have the bigger engine so it will not have to work quite so hard to maintain speed. And even if it does you can always step it down a mph or two with the cruise. I notice your location says 'midwest' which might disqualify you from this problem as well. There is no reason not to use cruise control for FE reasons when it's dead flat.

[cychosis]

I have read some threads here that talk about the cruise control being super dumb compared to a human driver.

I may be dumber than avg in that case, because on a few longish trips I tried the cruise control on my Gen III and was very impressed with it over the long haul -- yes, it tries to maintain speed up hill, but it never seemed to give the engine more than needed to do so. And on flats, it seems much better at holding the lowest possible acceleration, consistently without fluctuation.

I am sure the seasoned hypermilers here find it to be super useless -- but on the way back from the coast, I used it 80% of an 80 mile drive, including up over the coastal range (Oregon), and ended up with 55.6mpg. Seems pretty good.

[davidiiiii]

Thank you both for your responses. I'll feel much better next time I feel like being lazy and letting the car do the work

[qbee42]

Don't try to force the engine off. It won't help your mileage. If you haven't done so, you might want to read the sticky about improving mileage.

Tom

[davidiiiii]

Originally Posted by qbee42

Don't try to force the engine off. It won't help your mileage. If you haven't done so, you might want to read the sticky about improving mileage.

Tom

Thanks Tom, unfortunately I cannot find that sticky... Can you please link to it?

I don't understand why I shouldn't force the engine off and use electric if I'm going a steady 30-40mph.... If I don't do this, the engine usually stays on and I don't achieve the 100MPG status that I do when I purposely let off the accelerator and then hold it constant before the HSI midpoint line.

[patsparks]

If you use cruise on the highway then try one little trick to improve mileage.

Accelerate manually before you hit a hill. Bring your speed up maybe 5mph over cruise speed starting 100 metres before the start of a rise and hold your foot steady. Aim to just get down to cruise speed as you hit the crest of the hill and then let cruise control take over again. There is no need to disengage cruise, just help it along as it can't see hills.

Makes a difference but you can still relax.

[davidiiiii]

Originally Posted by patsparks

If you use cruise on the highway then try one little trick to improve mileage.

Accelerate manually before you hit a hill. Bring your speed up maybe 5mph over cruise speed starting 100 metres before the start of a rise and hold your foot steady. Aim to just get down to cruise speed as you hit the crest of the hill and then let cruise control take over again. There is no need to disengage cruise, just help it along as it can't see hills.

Makes a difference but you can still relax.

Great idea! Sometimes I wish we didn't have all of these screens with information. I cringe every time I accelerate

[spiderman]

Originally Posted by davidiiiii

Just purchased the Prius V last weekend, and although I love trying to maximize my mileage by using the HSI as a guide, it's honestly starting to stress me out!

Man, I hear you! I am in the same boat and I just can't keep from doing it. I really hate how the other drivers mess up my rhythm too. I was hoping that under the cold weather I would just let the mpg go and not worried about it but now I am really trying to keep things above 50 mpg! (more stressfull). One thing I did that helped a bit was block the lower grill. I saw at least a .5 mpg possibly a full 1 mpg. I was hoping someone else could confirm this.

Well try to relax dude and enjoy the car.

[qbee42]

Originally Posted by davidiiiii

Thanks Tom, unfortunately I cannot find that sticky... Can you please link to it?

Okay, here is the link:

New owner? Want MPG help? Read this first.

I don't understand why I shouldn't force the engine off and use electric if I'm going a steady 30-40mph.... If I don't do this, the engine usually stays on and I don't achieve the 100MPG status that I do when I purposely let off the accelerator and then hold it constant before the HSI midpoint line.

All of the energy in a Prius comes from burning gasoline. When you drive a Prius in electric vehicle mode (EV mode) the energy comes from the battery. This means the energy started out as gasoline, was burned in the engine to make mechanical energy which spins a generator to make electrical energy. The electrical energy is stored in the battery by converting it into chemical energy. To use this stored energy, the chemical energy is converted back into electrical energy. The electrical energy is converted back to mechanical energy in by the motor. That's a lot of conversions, and each one wastes energy.

When you get that great 100 mpg in EV mode it's like getting a cash advance from your credit card. You have free money for a month, but then you have to pay it back, plus 21% interest. When you borrow energy from the battery you have to pay it back with interest.

For good mileage, EV mode should only be used in a few special situations. The most common are creeping in stop and go traffic, and moving short distances where it doesn't make sense to warm up the engine. Otherwise you want to avoid EV mode.

Pulse and glide is another special case, where you accelerate hard with the ICE, and then coast, and repeat. In this case, obviously, you want to glide, not use battery power.

Tom