Better mileage with cruise control on/off or doesn't matter?

if you do a search here on PC with cruise control in the search box you'll find lots of posts on it.

 

If you are a good attentive driver you will get better mileage in any car (non just a Prius) if you do not use cruise control. Cruise control tries to hold a constant speed which means the car is constantly adjusting the throttle. If you hold the throttle constant and let the speed vary slightly the engine will run more efficiently.

 

I used to think thaty carefully usiong my foot (which i have done for decades) gave me beter mileage, that is until I bought the Prius. I am now convinced that using cruise control is much better that i now use it on the street (35MPH) and am getting better mileage there also.

I suspect that the electronic gas pedal/computer control combination is far more sensitive to tiny pedal movements than my traditional cars were. This observation came to me while carefully watching my wife drive around the same circuit without cruise control then the next day I would do it with cruise on. I would always get 4MPG better than her, despite the fact that pre-Prius she always got better MPG then me. YMMV

 

Don't know what type of terrain you have, but if there are any hills or traffic lights or other obstacles I cannot believe the cruise would do better than a human as it cannot anticipate those things and compensate for them. For example, if a steep grade is ahead you can speed up before getting there and then maintain your speed at a lower fuel usage than the cruise would do if it decided that it had to accelerate only once on the incline. Same goes for anticipating traffic or a light. On pure flat highway maybe it will do better, but things are almost never that perfect.

 

<div class='quotetop'>QUOTE(kirbinster\";p=\"103821)</div>

I understand what you are saying, in over 35 years if driving I would have agreed with you. All I can say is that my wife and I drive the same circuit to work (for the past 15 years) so we have very accurate number for what we experience. we have some hills but not a lot of the. We can anticipate traffic simply by touching the brake pedal 9the cruise control cannot anticipate stop lights either )

What is probably happening is that you have a lot more hills than I do and have developed your technique to suit. Since I am always able to drive at the speed limit, I choose not to speed up before a hill (too easy to get busted around here) but the average works out just fine for me. I do record our actual fuel usage numbers manually and also record the MFD display. They are within 1% of each other for the past year (but always disagree significantly on any individual fillup). when I tried not using cruise control, the MPG dropped significantly and stayed down there. It didn't matter who was driving the car, the results were the same.

Maybe you are just extraodinarily good at it.

 

<div class='quotetop'>QUOTE(Gen2\";p=\"103777)</div>

I'm finding the same thing. If the environment is good for using the CC then I also will engage it at 35 mph. Once I do engage CC I've noticed the the car will often slip into "stealth" 8) mode (battery). Its really hard to feather the go pedal to maintain a constant speed but not kick it and end up with the ICE running. I've found that up to about 45 mph the car will run for stretches in stealth under the CC. Above that it needs the ICE.

 

<div class='quotetop'>QUOTE(mehrenst\";p=\"103826)</div>

I'm finding the same thing. If the environment is good for using the CC then I also will engage it at 35 mph. Once I do engage CC I've noticed the the car will often slip into "stealth" 8) mode (battery). Its really hard to feather the go pedal to maintain a constant speed but not kick it and end up with the ICE running. I've found that up to about 45 mph the car will run for stretches in stealth under the CC. Above that it needs the ICE.[/b][/quote]

Excellent point. Now that you mention it, I do experience the same thing, a lot of stealth mode vs very very short moments of stealth mode when using my foot. That may explain it more than anything else.

Good catch

 

Interesting thread here, in my contacts with many pilots, regardless of good human conduct, an automated computer controlled "auto pilot" properly running, does it better, and more accurately then a man can. I know a bunch of 737 pilots that really prefer the auto pilots on approach then their own hands, and usually could do better and smoother for the folks back by letting the computer and ILS do the directional controls, while handling speed and altitude. I always missed that in the helo's, you had to control by hand 100% of the time, fixed wing had it made. As for cars, seems to me and from the other cars I have owned, that overall on a long trip the cruise does better then me. You do have to enjoy the trip some, and distractions ie kids, wife, cell, pets and what have you can hurt the mileage too., whereas the automated system is just that, it will do the better job overall. Of course in tricky situations, the cruise can cause problems, but those would deal more with safety, than MPG. Of course if you are really into the GREEN., then you can really monitor 100% yourself, sometimes you win and sometimes you don't. I'll take technology any day and use that, it seems Toyota knew a little more than me when they made this car.

 

I once installed an aftermarket CC for my corolla I bought at Sears. That system was a beauty! It sensed speed using the engine tach, assuming fixed engine RPM to wheel speed. For an automatic at cruise, this usually was a correct assumption. I had wished other cars would have done it that way, with speed monitoring in case of gear shifting or torque converter unlocking.
However the constant, unvarying hum of the ICE could put you to sleep!