Wayne, I apologize for my incomplete description.
At first I thought it was a problem with my TPS or something but then heard about the purge and figured it was that.

The car will surge, and FCD will suddenly drop 10-15MPG and if I don't disturb the throttle FCD will remain there for about 1-7 seconds then the FCD will begin a slower ~3 second climb to where the FCD was previously.

This may be what you are experiencing on your Insight after all. In my case it is completely random- One day I'll complete a trip and not notice it at all. Other times it is sometimes a series spaced a minute or so apart.

But I only REALLY notice it as I have a hill acent perfectly timed with exact load adjusted then suddenly a purge happens. (As Homer would say)......DOUGH! :lol:

 

To summarize my thoughts it depends on the length/grade of the corresponding inclines and declines. Assume my car gets 60mpg on a flat surface.

If I drive up a 6% grade for three miles (900 foot elevation gain) and then proceed down a 6% grade back to the original elevation it's a net loss because I cannot properly utilize all that free downhill energy since I would be dangerously exceeding the speed limit and experiencing massive wind resistance at the speeds generated by the downgrade in neutral. Plus since my engine still runs going downhill I'm still using some fuel.

However if that three mile 6% uphill gives me nine miles of 2% downgrade I believe I will come out ahead. Sure I may only achieve 35mpg for three miles uphill, but the 80mpg on the nine mile downhill will make this trip even or even a small net gain possibly.

Some real world examples:

The huge descent on I-80 into Salt Lake City is a huge waste of downhill energy since I have to stay in 5th and BRAKE to maintain a safe speed (under 85mph) on that incredible downgrade.

The ascent to the top of the "Grapevine" north of Los Angeles on I-5 is very steep and quick, but the resulting downgrade offers twentysome miles of very mileage-friendly downgrades of less severity. A great example of corresponding grades that are GOOD for fuel economy.

All depends on the length and severity of the corresponding grades IMO. I use this to my advantage, since I CRAWL up steep hills and milk as much free energy as possible going downhill in neutral.

 

Hi VX-Mike:

___First off, welcome to the Greenhybrid forum. With your fuel economy piloting skills, it won’t be long and you too will be added to a particular special list of members

___Now back to your climbing suppositions. There is only one problem. Unless you can figure out how to drive one way round trip, how do you get back home?

___I have seen past posts with much more extreme conclusions … I remember one about someone climbing mountains in their fathers SUV and receiving 10 up and had > 20 overall or some other such thing? Let’s take a Chevrolet Suburban up Pikes Peak and it receives an average of 6 mpg. On the way back down, we shut down the ICE and coast all the way down receiving an infinite mpg over that 35 mile or so segment. Impossible I know as I have driven that in our MDX but for the purpose of this exercise, it will do. What is the average? A lousy 12 mpg. You might have ¾ to 1 mile of coasting from 90 mph or what ever terminal is on a 2 - 3 % grade for a Suburban but it will still be darn close to an average of just 12 mpg round trip.

___And what does this all have to do with “Driving w/ Load”? Nothing really. Driving with load is a technique to trade off Kinetic for Potential and it works for hills of maybe 50’ to 70’ or less. Given the climbs being discussed here, you do not have nearly enough Kinetic to accomplish the trade off. Once you reach a minimum velocity, it is you and your cars frictional drag (of all types) vs. the Potential gained. Unfortunately, it is going to be one very painful climb because no matter how good your car’s aerodynamics and low friction components, there is never as much Kinetic energy gained on the downhill as the amount you lost in Potential on the way up.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___Waynegerdes@earthlink.net

 

Wayne,

True on the round trip vs one-way. Most of my miles are long distance freeway traversing many parts of the US, and I rarely drive the same route in both directions. I'm not used to thinking in that way, since I don't commute daily.

In fact "driving w/ load" works well for me in areas with numerous small hills. In fact my record tank was achieved along I-80 across Wyoming from Laramie westward which is filled with relatively minor hills.

 

I have some data on the bridge.
Again it is a bridge high enough for the world's largest super tankers to pass underneath.
I am traveling east; I never take it west.
The Vincent Thomas Bridge in Los Angeles California, actually it may be San Pedro.
If interested I'm sure you could Google it and find the specs.
The beginning and end are approx the same elevation, a few feet above sea level.
I have been holding the speed at 45, up and down.
I have about 10 passes.

In EVERY pass the MPG at the top was 1.1 or 1.2 worse than at the approach.
In EVERY case the MPG returned exactly to what it was before the bridge when I reached the bottom of the other side.
Since the data is not varying after 10 passes I feel it is reliable.

The MPG numbers are in the range of 62MPG and the tripmeter had approx 28 miles on it.

I stll want to experiment with the driving with the load technique.
I respect those here with more experience than I, and impressive MPG numbers.

Also, this is just one bridge.
YMMV, with other hill situations.
But in this case the data supports the conservation of energy.
What you lose to gravity on the way up is recovered from gravity on the way down.

 

I suspect the driving with load technique works best with lean burn engines, Atkinson engines, or diesel engines, all of which can run efficiently at low throttle settings. Since the standard ICE (with no lean burn) in my car runs less efficiently at low throttle settings, I find I get my best mileage on rolling terrain with downhills gentle enough that I don't have to do any braking (either friction or compression) to keep the speed from becoming excessive. Since my standard ICE runs most efficiently at about 70% throttle and below 2000 RPM, I can climb the hills at whatever speed this throttle setting gives me and then coast the downhills in neutral (and sometimes even with the ICE shut down). With my engine, this uses less gas than traveling the same distance on a flat road at a lower throttle setting.

 

Hi Basjoos:

___“Driving w/ Load” works to the tune of ~ 50% above EPA estimates in the Acura MDX and ~ 36% in the Toyota Corolla LE at their maximums. Neither of these automobiles have lean burn capability in the least. The MDX’s game gauge just like the Insight clearly shows the advantage of using this technique vs. steady and gas sucking cruise.

___I cannot wait to get a full tank in an 04 Accord or Camry 4 w/ Auto to see what they are actually capable of out on the highway using the “Driving w/ Load” technique as well. The Accord EX w/ NAVI does have a game gauge so I am going to take an I4 out for a drive next week just to satisfy my own curiosity as I have only driven the Accord non-NAVI for a short trip so far. That is if my local Honda dealer has an EX 4 w/ NAVI to take out for a half hour or so …

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___Waynegerdes@earthlink.net

 

All of know is that I drove 3 tanks using the driving with load technique and saw no MPG improvement over my usual climb and coast driving method. Although I don't have a game gauge to monitor fuel flow, I would maintain the same throttle setting I was using on level road as I climbed the hill and went down the other side, allowing my speed to drop on the uphill and rise on the downhill. Of course, I wasn't able to do as much coasting while driving with load since I started the downhill with less speed and did **** off more drivers by going slower over the crest of the hill.

Exel, do your Corolla and MDX have automatic or manual transmissions? My Civic CX has a manual transmission. Perhaps the transmission type may play a role in our differing results.

 

Hi Basjoos:

___Both the Corolla and the MDX are Auto’s, the Insight is a 5-speed of course. The MDX and Insight have game gauges. With their game gauges, I see as much as .5 mpg per hill when not using the DWL technique and I don’t get it all back on the downside. This continues until a lower overall average is achieved. With the DWL technique, fuel economy continues to climb up until a much higher overall fuel economy is reached. If I revert back in the X, the fuel economy begins to fall back towards that lower overall average I would achieve without this fuel saving technique. We are speaking of 3 entirely different types of automobiles + the Buick Le Sabre I drove on vacation throughout much of the Southwest a few weeks ago. The technique saves fuel in all 4 of these differing types of vehicles and I cannot see how it wouldn’t save fuel in your std. lean burn ICE equipped Civic. The fuel economy speaks for itself but that might be just be me as Eric Becky likes to point out

___As for messing with other drivers, Don’t. There isn’t always a driver behind you and you can do what you want when there isn’t. If there is, let them pass before you get to the hill otherwise don’t use the technique if it makes you feel uncomfortable.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___Waynegerdes@earthlink.net

 

My 1992 Civic CX hatchback doesn't have lean burn technology, it has the Honda 16 valve ICE from that period.

Exel, I notice that the four cars you list are having DWL experience with are either manual with lean burn (Insight) or are automatic without lean burn (Corolla, MDX, and presumably also the Buick Le Sabre), but no manual without lean burn cars were included (which is what my Civic is).

What I am wondering is whether the "boost and coast" technique I use in hilly and urban driving provides a similar amount of gas savings as DWL and that is why I didn't seeing any MPG improvement when I switched over to DWL.