My mother drives a Prius II, but I'm stuck with my dad's old Toyota Solara V6 auto. It gets 18-19mpg I live in Connecticut, and my town basically consists of huge hills. I was thinking, if I could just coast down all those hills ICE-off, I could save tons of fuel. Is this even possible?? And if so, would I see good gains in FE, or does stopping and restarting the engine take extra gas? I'm a bit hesitant to try it without getting some input first, for obvious safety reasons. For my morning drive to school, both big hills have stop signs at the bottom so I think it would be possible to crest the hill, turn off the ICE, and coast/brake all the way down to the stop sign, where I could start the engine up again.

Also, if that's not possible due to power braking/steering being off, would I see FE gains by shutting off the ICE at stoplights? I'm really not sure if stopping and starting the engine often is bad for it.

You are right. you will lose power brakes and stearing when you turn off the ice. Most hybrids have electric power steering to compensate. However, braking is still an issue in the IMA systems. You will get two or three good pumps and then your power brakes are out. Not sure about HSD brakes I think they are better suited but I have no real experience.

As far as shutting off the car at stop lights, it depends on how long you are stopped for. I think for hybrids 7 seconds seems to be about how long you have to stay stopped for to equal the gas you will use in restarting the engine. It may be longer for non hybrid cars. Also, you are going to increase wear and tear on the battery and starter since you will likely be shutting down 3 or more times when you normaly wouldn't. I'm not sure how robust these systems are. They may or may not be able to take it over a long period of time.

I would definatly turn off the engine if I were sitting in trafic and not going to be moving for at least 60 seconds.

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My scanguage say I use about .4 GPH(when warmed up) when idling or coasting in the Honda pilot.It has a V-6 3.5 liter-roughly the same as the Solara.It is about .0001 Gallons per second.At 50 mph a 700 ft hill coast would be 10 seconds or .001 gallon saved-or about .1 ounce(3 mls)-ten hills would save an ounce of gas-.
Now every little bit counts-but I think 100 seconds of redlight shutdown is a lot easier than 100 seconds of coasting with very heavy steering,marginal brakes etc.Besides,if you have an auto trans,I always worry that I will accidently shove it into reverse instead of neutral.I guess modern cars have some sort of"over ride" to prevent the trans from actually trying to engage reverse,but I'm not 100% sure of that.
Just shut down at redlights. 100 two minute lights should save about a gallon.Luck,Charlie

Turning off the engine is unwise as others have pointed out but there are several options:

1) predictive braking - slow down well in advance of a stop light that is red or likly to be red. This increases your probability of preserving some part of your momentum. Everytime you avoid a dead stop and 'glide', less fuel is burned.

2) idle down-hill - with a manual transmission vehicle, push in the clutch. This will let the engine turn over at the minimum revolutions going down hills and avoid burning fuel.

3) tune-up, inflate tires, change lubricants - let the engine have a chance to run efficiently. Fully synthetic motor oil and transmission fluid/oil can make a measurable improvement especially in cold weather. Fully inflate the tires and check them monthly is a good idea. Do NOT run with an over-filled motor oil.

4) Zen of driving - try to avoid momentum changes by 'driving the speed limit' and otherwise avoiding speed changes.

Good luck! But keep the engine running.

Bob Wilson

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I have never tried *any* of these tricks, so take what follows with a grain of salt:

How about popping into neutral at the top the hill with speed down to almost nothing, and then coasting down. The speed you accumulate at the bottom of the hill will be wasted, but that will be some 50% better than doing a constant speed over the hill.

Drive safely, first and foremost.

R2-E2, 2G Prius.
Highway/City/Husband/Wife MPG: 56.5, as of 12/2005, 26K miles

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this car [P2000] within this year [1998]. We will also make FCEV available in
2004."

If you simply take your foot off the gas pedal, and the engine RPM is well over 1000, literally no gas will be burned. If you press on the gas pedal lightly (as to try to counteract the "engine braking" even on a downhill) a small amount of gas will be burned.

If you're really curious, buy a ScanGauge and hook it up to the car so you can see the FE it's getting (or do many other things).

Not a good idea.

http://www.scangauge.com/

With fairly agressive driving our Grand Caravan always did around 16MPG.

We learned about FE with our HCH, and the wife is our main GC driver and thinks nothing of hypermiling.
However she has stopped the agressiveness and has slowed down...at least below 70MPH and averages around 20-21MPG.

I ran through a tankful with the GC using most of the techniques discussed on this site....with the exception of FAS, and switching to N in only extremely rare occasions (The shift is column mounted). If I were parked for a while like a fast food line I'd shut her off but otherwise kept it running and did almost 28MPG for that tank.

28MPG isn't too bad for a 2001 Grand Caravan V6.

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT

I turn both my manual tranny cars off all the time. It does save gas and it is dangerous so do it at your own risk. As has been pointed out the hybrids have electric power steering so while you lose power steering for a couple seconds it comes back after the "reboot". My Vette has regular PS which goes away if the ICE is off. It takes some muscles to steer so would not want to do this if you haven't had your Wheaties.

The brakes are a much bigger issue. Both cars will lose power brakes when the ICE is off and both cars are very hard to stop without power brakes. If your brakes are in good shape the vacuum will hold up for a stop or two depending on how smooth you put the brakes on. Every tap or pulse on the brakes bleeds off vacuum so you could run out of vacuum and lose power brakes in just one stop. If you are very smooth and deliberate with you application of the brakes and your brakes are in good working order you should have plenty of vacuum to stop at least once.

I only shut down my ICE on hills when there is not much traffic. When there is a lot of traffic safety should over ride gas savings and you should definately leave your engine on.

If you are going to be attempting this technique you should not do it in any traffic and you should also read up on power brakes at: http://auto.howstuffworks.com/power-brake.htm