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Myths about cruise control, highway speeds and mpg

badmix

badmix

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I got my Cruise control hooked up a few weeks ago. did a road trip this weekend, 120-130miles one way. I used CC on the way down. I had it set at 68mph (GPS verified), I was able to maintain CC for about 100miles, was nice not having foot on gas peddle, lol. But my gas mileage went way down. Normally I can make this trip using 1/4 gas or a lil more, using CC i used almost a 1/2 tank.

I just made the return trip today, didnt use CC, keep highway speeds between 70-75mph, more towards the 75mph mark, couple times had to hit passing gear. I only used a lil over 1/4 tank coming back.

So going faster actualy saves me gas. I guess 70-75mph is my trucks "sweet" spot for highway traveling.

Specs: 84' K5, 305cid (133k odo) 700r, 4:10s, 33 x 12.5 x 15, 2" lift.

I suppose I could try setting the CC at 75mph and see how it is. The one thing about CC, it cant see any grades or hills ahead, when your driving normal, you can anticipate these grades in the road and accelerate b4 hitting the grade so you keep the momentum up. With CC, it waits til the mph drops and then has to kick down a gear to keep up.

So, there you go, take it for what its worth, lol :D
 
I do fuel economy testing for a living and will say that your "test" is extremely flawed. You simply can't take a single vehicle and run one direction in certain weather conditions only one time, then turn around and run in the opposite direction only one time. You might as well say you drove uphill in a headwind going one direction and got terrible gas mileage, then turned around and ran downhill with a tailwind and got good gas mileage...but it was obviously because of the cruise control;)

Don't get me wrong here, but this is how internet myths get started. The next thing you know somebody will be making a post stating that somebody did a full blown nation-wide scientific study and determined that cruise control caused worse gas mileage.....
 
Not sure what to say, but both directions are Flat and Ive been driving this same stretch of highway for 3 months now. THe worst mileage Ive ever had was with CC. So, Id say its not as flawed as you predict. The only flaw was I shouldve ran CC up at 75mph. THe reason I Picked 68 was so I wasnt catching slower traffic and could maintain my lane.
 
For the test to be valid you would have had to go the same speed with and without cruise control. I would suggest that more than one trip would be necessary for a valid test.

I do know people that can keep their speed very controlled without cruise. But I myself have never found the cruise to decrease gas mileage
 
Also weather conditions will play a big role in the MPG, everything else being equal a headwind will be less MPG than having a tailwind. Also to get a fairly accurate MPG reading you would need to go through several tanks of fuel under varying conditions.
 
All of this said, I've compared cruise to non-cruise mileage and fuel consumption for the past 10 years or so, in a variety of vehicles, and the same result has held true in EVERY vehicle. Cruise DOES use more gas, and I can tell you why.

When you're driving along, most drivers slow going uphill, and accelerate going down hill. not a lot, but that is how most people drive. Cruise control will do everything it can to maintain speed up the hill, then use engine braking to maintain speed down the hill. The result? Significantly worse fuel mileage. In my years of casual observing, it's something on the order of 10-15% difference.

This is of course, assuming you're driving sanely. Trying to set new speed records, and the whole thing is out the window! :grin: That is my theory, and since it seems to be supported by my own observations, I'm sticking to it!
 
thedrip said:
All of this said, I've compared cruise to non-cruise mileage and fuel consumption for the past 10 years or so, in a variety of vehicles, and the same result has held true in EVERY vehicle. Cruise DOES use more gas, and I can tell you why.

When you're driving along, most drivers slow going uphill, and accelerate going down hill. not a lot, but that is how most people drive. Cruise control will do everything it can to maintain speed up the hill, then use engine braking to maintain speed down the hill. The result? Significantly worse fuel mileage. In my years of casual observing, it's something on the order of 10-15% difference.

This is of course, assuming you're driving sanely. Trying to set new speed records, and the whole thing is out the window! :grin: That is my theory, and since it seems to be supported by my own observations, I'm sticking to it!
Click to expand...

The solution for that would be to not use CC when pulling a hill but only while on flat land where it is most likely to help. I like having my own control while pulling a hill or running downhill versus using CC in this instance anyway.
 
OP is correct, I have verified with almost every vehicle i have ever driven. Only drives ive done with CC for max mileage have been 10+ hour drives i didnt have the endurance to do without CC.

still got 62+ mpg though :)
 
K5dreamer said:
2000 jetta TDI, manual transmission, 42psi in the tires, windows up, AC off, cruising at 55mph.

:thumb:
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Just to do a mine is cooler than yours here. One time my Dad and I got 57 mpg in a metro, going about 55 WITH cruise control on through Oregon. We were blown away when we figured it out. My Dad says he got close a couple of times. You could get above 50 if you tried

Car pretty typically got about 40 to 45 it didn't have AC

Thats a gas motor mind you
 
K5dreamer said:
2000 jetta TDI, manual transmission, 42psi in the tires, windows up, AC off, cruising at 55mph.

:thumb:
Click to expand...


Ah, OK. See now, I'm all in full size Chevy thinkin' mode and then ya go and pop off with a number like that. Then I'm thinkin' not if you shut the engine off and pushed it down the hill could you come up with a number like that!!:haha:

Even though its a thread about mileage with CC usage and doesn't necessarily have to be about FS GM's.:doah:
 
darned impressive for a gas engine..... is that 57mpg in US or Imperial gallons ;)

My goal with the jetta is to lower it, put upgraded nozzles on it, a custom tune, and a lower fifth gear ratio, and see if i can get 70+ mpg (US) cruizing on the highway.
 
K5dreamer said:
darned impressive for a gas engine..... is that 57mpg in US or Imperial gallons ;)

My goal with the jetta is to lower it, put upgraded nozzles on it, a custom tune, and a lower fifth gear ratio, and see if i can get 70+ mpg (US) cruizing on the highway.
Click to expand...

I thought TDI was Turbo Diesel Injection. :crazy:

Quick search found the answer. "Volkswagen TDI, or 'Turbo Direct Injection', is the Volkswagen Group's brand for its turbo diesel powered engines"
 
4X4HIGH said:
I thought TDI was Turbo Diesel Injection. :crazy:

Quick search found the answer. "Volkswagen TDI, or 'Turbo Direct Injection', is the Volkswagen Group's brand for its turbo diesel powered engines"
Click to expand...

I was complimenting Blazinuk for his mileage in his little gasser metro. trust me, if i didnt realize TDI was diesel, id have done quite alot of damage to my little jetta at the fuel pump by now. :D
 
K5dreamer said:
I was complimenting Blazinuk for his mileage in his little gasser metro. trust me, if i didnt realize TDI was diesel, id have done quite alot of damage to my little jetta at the fuel pump by now. :D
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Whew, thought you were saying your TDI was a gasser.

I had a buddy that bought a new Metro back when they first came out and he and i took a drive up to Reno Nevada (about 4 hours from me) and we got 61 MPG doing 70MPH. :eek1: That surprised the hell out of me but that car was just too small for me to ever think about owning one.
 
4X4HIGH said:
:eek1: That surprised the hell out of me but that car was just too small for me to ever think about owning one.
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Ha when I had my Metro I was 6'3" around 245, the headliner was in great shape except the hole my head wore in it!!!!

Had a friend who built a header for his Metro rebuilt the engine put coatings on the pistons and heads did an ignition system lowered it a bit. Couple of other things, his would get 60MPG doin 75 no problem. Thing is he got some kook to pay for all his mods!
 
Best mileage I ever saw was about 42 mpg in a 4 door Chevy Nova... That's right, a Chevy Nova, no lie.

.

.

.

.

But...

.

.

.

.

It was an 86 Chevy Nova. A re-badged Toyota Corolla that Chevy was buying from them and selling as thier own commuter car.

But still, 42 in a Chevy baby.
 
I deal with people like this on a regular basis at work. Inventors, backyard mechanics, etc... that have come up with some miracle device to increase fuel mileage and advertise crazy mileage gains based on exactly this type of "test".

Again, don't get me wrong. You definitely could of got worse mileage using CC and your experience would be considered an indicator. The explanation of CC applying more throttle (fuel) to maintain speed on a grade is legitimate, but only if the person driving does indeed allow the vehicle to slow down. However saying that the CC uses engine braking going downhill and thus uses more fuel is completely irrelevant since there is no normal function within cruise control that does this....same thing as just letting off the gas pedal and coasting.
 
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