Cruise Control MPG

[ManWonder]

For many years, I have relied on using cruise control while driving any of my vehicles. But on a recent trip in my 2004 Roadtrek 190 Popular, I found I got way better gas mileage by avoiding the use of cruise control. Now, obviously there are times when one does not want cruise control to ramp up the RPMs just to go up a hill when there is no hurry and traffic is light. But beyond that kind of waste of gas, I was surprised foregoing the use of cruise control yielded such a benefit (3-4 MPS). Granted, I should do a lot more travelling to ensure this trip was not a fluke but I was just wondering if others have had the same experience.

[BBQ]

.

If you want to get better MPG,
install a vacuum gauge,
and work the gas paddle based on the vacuum,
you will get excellent MPG that way.

[booster]

Not unusual at all to get better mileage than the cruise. Getting better mileage on cruise is one of the huge myths, IMO.

With the Chevies, in particular, keeping them from down shifting when on hills or reaccellerating after a slowdown can be a huge difference in mileage, like in 2+mpg. Also always get you foot all the way off the gas whenever possible, as the Chevies shut off all fuel that way, which is worth some mileage for sure, especially in the hills. If driven carefully, we actually get a better mileage in hills than the level, for that reason.

[mkguitar]

3-4 MPG is alot

on levelish ground I doubt I could keep as steady speed ( which is high vacuum) as well as the CC.

the 3spd wO/D makes for more "drastic" variation is rpms when on hills.
that where the newer 6 speed tranny will be better at keeping the rpms in a better range for power and economy

Now that I have a realtime fuel consumption display available ( thank you forum for help with OBD reader)- I'll be better able to see for real than guess over a tank full

In many cases I get better control in hills by manually controlling shifting or using tow/haul *( which is useful on the van, useless on my 2001 sierra)





Mike

[booster]

Originally Posted by mkguitar

3-4 MPG is alot

on levelish ground I doubt I could keep as steady speed ( which is high vacuum) as well as the CC.

the 3spd wO/D makes for more "drastic" variation is rpms when on hills.
that where the newer 6 speed tranny will be better at keeping the rpms in a better range for power and economyMike

I think the real point of why the cruise gets worse mileage is here, and why folks misunderstand. The biggest deal is to keep the throttle position and the load within the "sweet spot" for mileage, and speed alone won't do it. That is why cruise is inefficient. BBQ is on track with the vacuum gauge, but these days the manufacturers also play a lot with EFI programs and spark timing, so you are better off to watch a Scangauge for instantaneous mileage, or fuel per hour. Injector pulse width is also is pretty good, but the fuel pressure changes can make it less accurate. I think most folks would be very surprised on what makes it better or worse. One point is that with a Scangauge, and maybe other similar products, you can reset the trip data on the fly, so you can repeatedly see what affect things your are doing over variable time periods, like steady level or rolling hills, whatever. It is extremely useful a feature.

On my old Ford Escort wagon (1992) with a 1.9 split port engine, I would get substantially better mileage by accelerating faster than slower, which violates every rule. The key was to keep it from going to full rich mode while doing, which left the mixture the same as doing it slowly, but got the vehicle up to speed faster, so it could be in "lean cruise, which was over 17 to 1 air fuel ratio with that engine.

The only way to really find out what makes it better and worse is to watch the short term fuel use, and then confirm with long term use once you figure out what you think helps and adjust your driving style.

[ManWonder]

Originally Posted by booster

Not unusual at all to get better mileage than the cruise. Getting better mileage on cruise is one of the huge myths, IMO.

With the Chevies, in particular, keeping them from down shifting when on hills or reaccellerating after a slowdown can be a huge difference in mileage, like in 2+mpg. Also always get you foot all the way off the gas whenever possible, as the Chevies shut off all fuel that way, which is worth some mileage for sure, especially in the hills. If driven carefully, we actually get a better mileage in hills than the level, for that reason.

Good info! I found I actually kind of liked driving without cruise control; I felt more in control. My foot got a little cramped and so I moved my seat up a notch and that seemed to help. Basically I just stayed in the right lane and did what the truckers usually did. I really appreciate y'all sharing your insights.

[avanti]

Be careful not to overgeneralize. The above analysis is probably correct for traditional cruise controls, which are basically bolt-on devices. But current generation vehicles have many interacting safety and convenience features that all communicate via CANbus, and so have at least the potential to have complete visibility into engine parameters. My 10 year old Sienna has an adaptive cruise control that can brake as well as accelerate in order to maintain vehicle distance. I have no data on what is going on now, but as we creep toward autonomous vehicles, it becomes increasingly plausible that cruise controls will become "smart" WRT fuel efficiency.

[booster]

Originally Posted by avanti

Be careful not to overgeneralize. The above analysis is probably correct for traditional cruise controls, which are basically bolt-on devices. But current generation vehicles have many interacting safety and convenience features that all communicate via CANbus, and so have at least the potential to have complete visibility into engine parameters. My 10 year old Sienna has an adaptive cruise control that can brake as well as accelerate in order to maintain vehicle distance. I have no data on what is going on now, but as we creep toward autonomous vehicles, it becomes increasingly plausible that cruise controls will become "smart" WRT fuel efficiency.

I would agree on the technology. Our 2007 has drive by wire, but not a lot of other stuff. The big problem with cruise, I think, is that the top, and very tight, requirement, is to hold speed consistently, and everything else is secondary. They also have a "typical" acceleration rate to get back to speed when you hit resume after a slowdown, which is much faster than a high mileage acceleration rate. All of things are based on driver preferences for "feel", and seem to way off from getting top mileage.

When driving by hand, you run up speed downhill by coasting and then giving a bit of boost power at the bottom, and let it lose speed uphill to prevent high throttle settings and downshifts. High mileage driving style is not what most drivers want to have, and most of us don't want it in front of us either. If you have ever been behind a hypermileing Prius, you know what I am referring to, so the cruise is not programmed to do that kind of drive, even though it could be in nearly all cases these days.

[g1g]

Originally Posted by ManWonder

For many years, I have relied on using cruise control while driving any of my vehicles. But on a recent trip in my 2004 Roadtrek 190 Popular, I found I got way better gas mileage by avoiding the use of cruise control. Now, obviously there are times when one does not want cruise control to ramp up the RPMs just to go up a hill when there is no hurry and traffic is light. But beyond that kind of waste of gas, I was surprised foregoing the use of cruise control yielded such a benefit (3-4 MPS). Granted, I should do a lot more travelling to ensure this trip was not a fluke but I was just wondering if others have had the same experience.

While I have put a good effort into getting better MPG without using cruise only a couple times I can say i have successfully been able to hold my control and succeed. I now almost always use cruise and as a general rule get better MPG. I have told a number of my friends about better MPG with cruise and every single one of them have switched to using cruise. All the people I work with have also switched to using cruise traveling to work everyday for the same reason as we all travel about 20-25 miles each way.

[booster]

Originally Posted by g1g

While I have put a good effort into getting better MPG without using cruise only a couple times I can say i have successfully been able to hold my control and succeed. I now almost always use cruise and as a general rule get better MPG. I have told a number of my friends about better MPG with cruise and every single one of them have switched to using cruise. All the people I work with have also switched to using cruise traveling to work everyday for the same reason as we all travel about 20-25 miles each way.

In your case, you do seem able to improve economy by hand driving instead of cruise, but have decided that it isn't worth it, if I understand correctly. That is similar to what I do, in reality. We drive way to fast for good economy most times, and often use the cruise as it is easier and worth the extras gas. A couple of times a year, I will do a best mileage check run just to make sure the van is running properly, but don't obsess on it now that we know what it will do and how to do it if we chose to. For us going faster (67mph average on a cruise setting of 72/73mph) vs slower for mileage (50mph average on a driven speed of 55mph) is just about 2-3mpg or so (14.5 vs 16.5mpg give or take). Not dieing of boredom on long drives is worth the extra gas

It all depends on the vehicle and driving style. The way many folks drive in normal driving is very contrary to good fuel economy, so going to cruise is likely to help. Careful drivers can almost always do better off of cruise, under most conditions, but it is a learned skill like many others. I can tell you that the hypermilers never use cruise, and neither do any of the economy competition vehicles.

[g1g]

I believe the better MPG from cruise results in the cruise will hold the steady speed where without it my and my friends and coworkers foot gets a little heavy therefore using more gas.

[booster]

Originally Posted by g1g

I believe the better MPG from cruise results in the cruise will hold the steady speed where without it my and my friends and coworkers foot gets a little heavy therefore using more gas.

I am sure you are correct, plus, at least around here, commuter traffic seems to run in waves with lots of 20mph or more up and down speed oscillations, so setting cruise to average them out would surely help compared to dashing ahead only to slow down again.

[ManWonder]

Originally Posted by booster

Also always get you foot all the way off the gas whenever possible, as the Chevies shut off all fuel that way, which is worth some mileage for sure, especially in the hills.

So, after chewing on this for a while, I have to say I am puzzled. If Chevy cuts off the fuel when the foot is off the gas, what keeps the engine idling at stops?

[booster]

Originally Posted by ManWonder

So, after chewing on this for a while, I have to say I am puzzled. If Chevy cuts off the fuel when the foot is off the gas, what keeps the engine idling at stops?

That is an interesting question, I will have to do some reading on that. My quote about shutting off the fuel came from an explanation referring to why the Scangauge goes to 9999 when you are a coasting, from Scangauge.

My best guess would be that they are also comparing to the vehicle speed sensor, and turning the fuel back on as you reach idle speed as coming to a standstill. The torque converter keeps the engine turning as you decelerate, although slower than if you were cruising with the engine pulling, so they would have to pick a point to turn on the fuel while the engine was still turning enough to start running again. I can say I have never felt it happen that I remember, though.

I think we should be able to see what happens by watching the Scangauge as we come to a stop, as at some point the 9999 should go back to a regular mileage number, I think, before being completely stopped.

Very good observation!

[Manx]

Wow, I haven't thought of this before. Apparently there is a lot of debate connected to whether it's better to coast in neutral or in gear in automatics.

Examples:
Fuel Injector Shut-Off | CleanMPG
Fuel injector shutoff while coasting on an automatic? - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
Fuel Injector shut-off while Coasting - Fuelly Forums

From my limited reading, "modern" automatics shut off fuel flow when decelerating in gear, but not in neutral? And reengage fuel flow if rpm falls low? Something like that.