Here's what pulse 'n' glide will get you.

[Clev]

I borrowed my wife's car ('04 Saturn Ion, 5 speed, wide performance tires) to visit my folks for a few days. My drive was from Southern California (San Bernardino mountains) to Stockton (Central Valley), about 413 miles each way.

On the trip up, I tried a limited pulse and glide, from 60 mph to 75 mph, with the engine in neutral (can't install a "kill" button in the wife's car, and didn't want to wear out the ignition switch.) I did turn the key off during the downhill glide down the Grapevine. There was moderately heavy traffic, so I couldn't do a lot of P&G (my policy is that if I hinder other cars, I'm just wasting their gas, and what's the point then?) I also did a P&G on the air conditioner, turning it on medium-high until I was uncomfortably cold, and them switching it off and recirculating until it was uncomfortably warm. (In 85+ degree weather, I could generally leave it off 6-8 minutes for every 2 minutes on.) Average speed when not in P&G was 68-72 mph, and 10 miles were on a rough country road. Overall average, 35.05 mpg, which is 4 mpg higher than I ever got in normal (62 mph) driving!

The return trip was Wednesday evening. The traffic was much lighter, so I could P&G quite a bit more, again, either 60-75 or 60-80 depending on how big a gap in traffic I could work with. The cooler temperature meant longer P&G cycles on the A/C, and after a couple of hours, I could turn it off entirely and just run the fan. This time, the trip included the reverse run over the Grapevine (over 15 miles of gliding with the key off!), three stops, and my normal run up and down the hill at home (4,675 feet.) When I filled up this morning, I got 39.09 mpg! This is on a car freeway rated at 32 mpg. Total savings: about $17 vs. my normal 31 mpg in this car.

I can't wait until I get the clutch leak fixed on the Honda--a kill switch will be the first mod!

[Daox]

Very nice example!

[pasadena_commut]

Originally Posted by Clev

I did turn the key off during the downhill glide down the Grapevine.

Stupid move. Maybe you saved a buck on gas but it damn well wasn't worth the risk. I have driven the Grapevine at least 50 times each direction. Sure, often one can coast down into the central valley and never even tap the brakes. However, bad things happen really fast on that stretch of road, and with a mountain on one side and a cliff on the other, whatever else happens on that grade, getting off the road is not an option. Stomping the brakes may not get you out of trouble, sometimes the only way out is to punch the gas (and pray). Example, the semi merging blindly into your lane from the right while there is traffic on your left and another car behind you. Even stomping the brakes may not work as well as you think when you're doing 70MPH down that grade and find you need to come to a complete stop. Once the boost goes, is your leg strong enough to stop your car under those conditions?

Besides being dangerous (when a bad situation presents) it is also likely pointless. Many cars, your's probably included, won't burn a bit of gas on those steep downgrades - the injectors will shut off. Heaven forbid that anybody would put it in neutral on such a road, as the engine braking will keep the car near the speed limit without burning out the brakes.

[Clev]

Originally Posted by pasadena_commut

Stupid move. Maybe you saved a buck on gas but it damn well wasn't worth the risk. I have driven the Grapevine at least 50 times each direction. Sure, often one can coast down into the central valley and never even tap the brakes. However, bad things happen really fast on that stretch of road, and with a mountain on one side and a cliff on the other, whatever else happens on that grade, getting off the road is not an option. Stomping the brakes may not get you out of trouble, sometimes the only way out is to punch the gas (and pray). Example, the semi merging blindly into your lane from the right while there is traffic on your left and another car behind you. Even stomping the brakes may not work as well as you think when you're doing 70MPH down that grade and find you need to come to a complete stop. Once the boost goes, is your leg strong enough to stop your car under those conditions?

Besides being dangerous (when a bad situation presents) it is also likely pointless. Many cars, your's probably included, won't burn a bit of gas on those steep downgrades - the injectors will shut off. Heaven forbid that anybody would put it in neutral on such a road, as the engine braking will keep the car near the speed limit without burning out the brakes.

Having driven that a couple hundred times myself, I'm pretty comfortable with it. I only keyed off during the more gentle downhill portions, and I did refire it once I got to the final steep decline where I needed the engine braking.

As to the injector shutoff, that's fine if you need the engine braking, but there were several very gentle declines (especially between Gorman and Lebec) where leaving it in gear would rob me of momentum and consume more gas as I pushed the pedal to maintain the speed limit. Likewise on the return trip, between Frazier Park and pretty much Santa Clarita, I was able to leave the key off. No traffic to speak of, and the decline is so gentle that I would have been on the gas the whole time had it been in any gear.

[Clev]

Slightly down this fill-up, to 32.74. Checked my tire pressure at the gas station, and the left rear was down to 20 psi! Crap.

Aired it back up to 48 mpg (rated to 51), and I'll keep a closer eye on it.

[pasadena_commut]

Originally Posted by Clev

Slightly down this fill-up, to 32.74. Checked my tire pressure at the gas station, and the left rear was down to 20 psi! Crap.

Aired it back up to 48 mpg (rated to 51), and I'll keep a closer eye on it.

Where can I get some of those 48 mpg tires? (Just kidding.)

When a tire drops that much pressure it needs more than "keeping an eye on it". If it were my tire I'd take it in to a tire shop. Most likely this is just a nail or screw in the tire that you have not spotted yet, maybe jammed up between the treads somewhere. That would be easy and cheap to fix. (Unlike my last tire failure, which was a big nail sticking out of the sidewall, which necessitated the replacement of the tire.)

[Clev]

D'Oh! Yeah, that's 48 psi.

I haven't checked the pressure in that tire for over 2 months, so it's a very slow leak. I didn't find any nails or damage when I looked at it, but this weekend I'll dismount it and try some soapy water to see if I can find it.

[pasadena_commut]

Originally Posted by Clev

I haven't checked the pressure in that tire for over 2 months

That's too long, especially if you drive on the highway every day.

I'm not a pilot, but I have fallen into the habit of making a quick once around before driving the car, at least every other day, and always if I will drive on the highway that day. This takes all of 5 seconds. A gauge is used every other week (by which point they are usually down about .5 psi). The visual inspection is actually the most important one safety-wise. A seriously under inflated tire is easy to spot visually, and since these usually result from a puncture where the air loss is quick, even checking the pressure once a week would not be frequent enough to catch the problem before driving on the low tire. The walk around won't catch a tire down from 33 to 28, but I'm sure I would notice a tire at 20 psi or less.

[Clev]

Originally Posted by pasadena_commut

That's too long, especially if you drive on the highway every day.

I'm not a pilot, but I have fallen into the habit of making a quick once around before driving the car, at least every other day, and always if I will drive on the highway that day. This takes all of 5 seconds. A gauge is used every other week (by which point they are usually down about .5 psi). The visual inspection is actually the most important one safety-wise. A seriously under inflated tire is easy to spot visually, and since these usually result from a puncture where the air loss is quick, even checking the pressure once a week would not be frequent enough to catch the problem before driving on the low tire. The walk around won't catch a tire down from 33 to 28, but I'm sure I would notice a tire at 20 psi or less.

Agreed, you're absolutely right. I had been driving my wife's car for a couple of weeks, so I didn't really notice the lack of acceleration (though I did note the lack of coasting, and stupidly it didn't really register.) I'll check it on every fillup to see what I'm up against.

[Piwoslaw]

While reading how Clev was P&G'ing not only the car, but also the A/C, I started thinking where those two thing could/should be coordinated? If I want to P&G my A/C, then is it better to turn it on while while the car is already under power during a pulse, or when I'm coasting in neutral? I turn off the A/C when I really need power, like uphill or passing a truck, and turn it on when engine braking. But during P&G in normal conditions when is it better to put an extra load on the engine?