[charis]

I got to wondering about the cruise control comments on various threads; does anyone think the cruise control can or will do better than someone who pays very close attention to maximizing fuel economy?

For the sake of discussion I'm assuming no interference from other traffic.

IMNSHO I have yet to use one in any vehicle over several decades that is as obsessively anal as I can be... :icon_redface:

In their defense I perhaps worry a bit less about very minor speed fluctuarions. :biggrin:

 

[crewzer]

Our current three vehicles (Subaru, Honda, Ford) are equipped with CC, and perhaps six vehicles before {Plymouth, Ford, Acura (2), Honda, Pontiac} were also equipped with CC. I’ve seen consistently mixed results from its effect on fuel economy.

In short, CC seems to help with fuel economy and driver comfort on flat roads, be they level or uphill. For example, CC seems to work great while running I-40 across eastern Arkansas or the long, gentle uphill climb west on I-80 through Nebraska.

However, since CC is reactive, it doesn’t seem to help on variably-hilly roads such as I-81 through Virginia. Specifically, vehicles operating on CC typically slow down a bit when transitioning from a downhill run to an uphill stretch, and the CC applies extra gas to accelerate the vehicle back up to target speed before dialing back a bit to maintain speed.

Accelerating uphill usually does not promote good fuel economy. Accordingly, I rarely use CC on hilly interstates, preferring instead to proactively apply a bit of extra gas as I approach an uphill section, although, if conditions warrant, I may use CC but manually override it a bit when approaching an uphill section.

I’ve also found that CC seems to “hunt” on long downhill runs, such as I-80 eastbound in Nebraska. I doubt that this behavior helps with fuel economy.

YMMV.

HTH,
Jim / crewzer

 

[bbottomley]

I haven't studied its effect on fuel economy, but whether it adds of detracts a bit in that department, it sure cuts down on the fatigue I would feel in my gas pedal leg after an all-day drive.

It's also handy to ensure that I stay within the strictly enforced 25 MPH limit on certain military bases that I frequent!

 

[Canonshooter]

However, since CC is reactive, it doesn’t seem to help on variably-hilly roads such as I-81 through Virginia. Specifically, vehicles operating on CC typically slow down a bit when transitioning from a downhill run to an uphill stretch, and the CC applies extra gas to accelerate the vehicle back up to target speed before dialing back a bit to maintain speed.

Accelerating uphill usually does not promote good fuel economy. Accordingly, I rarely use CC on hilly interstates, preferring instead to proactively apply a bit of extra gas as I approach an uphill section, although, if conditions warrant, I may use CC but manually override it a bit when approaching an uphill section.

Before my turbo upgrade and tune, my stock FXT used to do just this. It was really annoying to have the car jump into passing gear on long, uphill grades of the interstate.

However, now tuned to the current level of torque, this no longer happens. In fact, the torque converter doesn't even unlock - it just muscles up the hill without a change of RPM.

I do find a slight improvement in fuel economy, no cramping in my right leg and no worries about creeping to far over the speed limit. In short, I am a BIG fan of CC on long hauls.

 

[Real Lyte]

CC has only caused poor gas mileage here, our Interstate is hilly so it doesn't negotiate shifting well.

 

[stan_t]

What model do you have? I don't like CC on my XT and avoid using it. It makes the car get into boost very aggressively, I drive alot smoother using my foot which results in better mileage.

Stan

 

[Canonshooter]

What model do you have? I don't like CC on my XT and avoid using it. It makes the car get into boost very aggressively, I drive alot smoother using my foot which results in better mileage.

Stan

Stan, mine did the same after my initial tune. I had the throttle re-mapped less agressively and it made a world of difference!

 

[Tuned200]

I always run cc on trips. I cant comment on if my mileage is better or worse but typically I get 25-26 with cc and 17 in city.

 

[YVR Fozzie]

I can consistently out perform my CC on hilly OR flat roads BUT the fatigue factor is the reason I use cruise. Having said that, I'm pretty smooth and have over 1 million kms behind me (not on the Subie... yet!) so I treat the accelerator as if it has an egg between it and my foot (and SOMETIMES you need to SMASH that egg to bits!)

 

[jheisler]

on my 2010 forester it actually hurts the mileage. When I put it on 72mph on CC I get 22.8 where as when just driving I will get 23.8 from varying speeds from 70-75

 

[1stsubie]

Really...?

I can agree with most comments on this post regarding CC and terrain conditions. Nevertheless, I seem to get better milage while using CC in most instances. My '09 FOZ can get really close to 29-30 mpg when cruising with it on, otherwise it pegs at 26-27 with foot modulation. My '10 Corolla (which I drive 130 miles daily) while driving on flat to mixed terrain with CC on gives me 37-38 mpg, with it off I average about 35 mpg. On a side note, I feel that niether my FOZ or ROLLA modulate accel and decel that well when encountering hills. I had an '06 Honda Pilot that was brilliantly tuned for CC on hills. It would actually hold my speed down a hill, I almost wondered if it needed to downshift to do this but never felt it or saw the tach peg. On up-hills the tranny was tuned to hold the shift, which was nice, and would kick down to a lower gear and hold it there. The FOZ and ROLLA are a bit more erratic and hunt for gears, sometimes getting to speed shifting up and then down again to get back up to speed. There are two hills on my commute that I kill the CC because both the ROLLA and FOZ will downshift too late and then I'm at the top of the hill. Nevertheless, I'm a fan of CC and use it all of the time.

 

[Matrix11229]

I like to use CC and so far I get better mpg with it. My wifes Legacy has a mpg monitor and I was testing the CC to get better MPG. CC works best on flat highways, but even on hilly roads it can perform better if you know how to use it. I managed to get 36mpg average on the Legacy driving 100 miles from CT to NYC.
On hilly roads I usually acclerate downhill to a maximum speed which gets reasonable mpg, and then slowly deccelerate uphill by pressing the coast/- button repeatedly.
MPG monitor helps a lot to get the maximum out of CC. I wish I had MPG monitor in the Forester.

 

[106rr]

I get a little better mileage with the CC in my 09 Ltd Foz and in my Acura SLX, a little worse mileage with my 01 Infiniti I30. I still use the CC a lot. I think it depends on the individual model and the terrain. I often disable the CC in the Sierras or other steep mountains. I also use the sportshift to keep the Foz in 3rd on long ascents.

 

[FLdrummer]

I haven't tried the Forester in the mountains yet using CC, but here is my observation from driving a Tacoma Prerunner with AT and 3.4L V6 in the mountains (specifically, I-40 from Winston-Salem to Asheville, NC).

1. It depends on the speed and engine RPM. If the CC is set to a speed that the power output and gear ratio mesh well with momentum, then the transmission won't hunt gears much. In the truck, that seemed to be either 60mph or 70mph. At these speeds if the vehicle shifted gears, it would only drop to 3rd. But when set at 65mph it would quickly jump down to 2nd gear fairly often.
2. On some steeper segments disable overdrive. Let CC pull the hill in 3rd (or the 1:1 ratio gear). No gear hunting when set at 60mph in the truck with overdrive disabled. Granted, this can be dangerous when overtaking slower vehicles since the CC will keep on pulling when one might otherwise prefer to slow up a bit by just letting off the gas.

The truck got just over 21mpg in the flatter territory using CC. It got just over 19mpg in the mountains. So I saw about a 2mpg impact due to terrain.

I haven't figured out exactly how this would translate to the manual transmission on the Forester. Will get to learn that soon enough though.

 

[FLdrummer]

Oh...forgot...CC impact on fuel efficiency. I was using CC in the Forester the time that I pulled nearly 34mpg in Central Florida. Set CC at 50mph in the continuous city sections. Otherwise set CC just under 65mph in the rural areas. Timed the trip to miss rush our traffic and made surprisingly good time, even at the slightly slower speeds. Good fuel economy and good trip times - 2 for 1 on that trip. :biggrin:

 

[Brandon]

Cruise control improves my gas mileage on the interstate simply because it gets me to settle down and listen to my music rather than enjoy my car. I drive much slower and I'm much less prone to sudden outbreaks of "Holy crap this is taking forever! Let's go FASTER!" The mileage penalty of my foot on the pedal is bad enough in those cases, not to mention the fact I'd need to improve gas mileage like 200% to offset the number of speeding tickets I'd get without CC.

Yeah, I could probably get better mileage in most scenarios if I were willing to pay attention to minute details and make a constant effort to conserve fuel. But realistically, that's never going to happen with me. Plus, that sounds like even less fun than driving on the interstate already is.

 

[OldGoat38]

In the case of my wife's '09 outback with 4AT, CC is no help in hilly terrain. The engine goes from borderline lugging to screaming depending on the whims of the transmission. A 5 or 6 speed AT probably would do much, much better.

With my '12 Forester with 5MT, CC is great. On the same hilly terrain the engine stays in 4th or 5th (whichever I choose). If the terrain were so hilly that I'd need to downshift, then I'd turn off the CC.

I think the CC helps MPG somewhat and is great to avoid speeding tickets.

 

[MN2011XT]

It's flat around here so yay for CC. I wish my taco had it. I have a heavy foot.

 

[SierraHotel]

Here is Edmunds.com take on cruise control's effect on mpg. They seem to agree with most of the comments in the previous posts, including the comments on mountain driving:

"Using cruise control is a bit of gas-saving advice frequently on tips lists. We have always agreed with this tip in theory but we hadn't expected such significant results. First, it smoothes out the driver's accelerator input by preventing nervous "surging." Second, it makes the driver take the long view of the road rather than reacting to every change in the traffic around them.

Method: We did this test twice with four different cars each time driving the 55-mile loop. The first time we set cruise control to 70 mph. The second time, with the cruise control off, we varied our speed between 65 mph and 75 mph. We tried to mimic the driving style of a person who is in moderate freeway traffic.

One thing that's important to note: if you are in a mountainous area you should turn off cruise. It will try to keep you up to the speed you've set and will use a lot of extra gas downshifting to lower gears to accomplish this."

 

[MXForester]

I drive 250-400 miles a day. I use CC every chance I get. For me it's a fatigue thing. I've had my '12 a little over a week. First tank was 25.5. Since then they've been in the 29s. It's also been over a hundred degrees here everyday in that timeframe with the A/C on the second notch all day, every day. I'd like to think I could have broken 30 by now.

Or maybe not.