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Cruise control fuel consumption.
#1
Short and simple.
Do you get better fuel consumption with or without cruise control engaged?

Seems to me better without.
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#2
I reckon I get ever so slightly better but I do have a 37 mile drive to work which is mainly dual carriageway over the South Downs.


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#3
Not Berlingo but Honda : I get 2 mpg less on motorways and when I drive door to door purely on the buttons ( shouldn't really I suppose ) I get much the same.
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#4
2004 2.0HDi, I get about 4mpg less using cruise control than I do driving normally.

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#5
Every hill you come to, cruise will "open the throttle" to maintain the set speed. I have even had it shift down a gear on my automatic Merc when towing to achieve this.
When you drive without cruise, you tend to allow speed to fall off a bit going up hill which you regain when going down the other side, whereas cruise will slavishly try to maintain that speed up hill and down dale (going downhill, my Merc downshifts so engine braking holds the speed back if it exceeds the speed set on cruise)
This is why cruise uses more fuel (unless on a really flat road)
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#6
(22-03-2016, 08:16 AM)Col Wrote:  Every hill you come to, cruise will "open the throttle" to maintain the set speed. I have even had it shift down a gear on my automatic Merc when towing to achieve this.
When you drive without cruise, you tend to allow speed to fall off a bit going up hill which you regain when going down the other side, whereas cruise will slavishly try to maintain that speed up hill and down dale (going downhill, my Merc downshifts so engine braking holds the speed back if it exceeds the speed set on cruise)
This is why cruise uses more fuel (unless on a really flat road)
We can also take advantage of the descents, where accelerating to get to speed is easier and less fuel consuming, and then use the picked up speed for the next hill. The cc does not do this, it only throttles off when going downhill and goes full whack uphil to maintain the speed.
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#7
My personal best of 60.something mpg was when I was using cruise control for about 95% of the journey. I understand the theories about the downside, but I haven't seen it happening in practice.

Mine's never shifted down while cruising, and I don't think it's clever enough to downshift to engine-brake if it goes too fast. If you're going downhill in 6th gear then it will coast up to whatever speed it would do if you were driving manually in 6th - it doesn't care if you go over, although this almost never happens anyway. You don't get hills steep enough on the sort of roads where you'd normally be cruising.

It's hard to actually measure a difference of a few mpg. The air temperature, variations in diesel, how busy the roads are or what mood I'm in good all make this kind of difference, among many other factors. So it's easy to get fooled by checking too much, to too high an accuracy.

I reckon that there are probably efficiency gains to be had from going at exactly the same speed. There's a sweet spot, somewhere around 60mph - if you do either 50 or 70 then the mpg will probably be lower. So it's best to keep it at the ideal speed and not wave around into less economical speeds.
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#8
Even If CC delivered 10 mpg less than manual driving (which it doesn't), I'd still use it all the time like I do now. I regularly drive from Leeds to Plymouth and back in a day, and my right ankle would be killing me at the end of the journey if I did not have cruise control.
[+] 1 user says Thank You to CourierJim for this post
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#9
(22-03-2016, 08:31 PM)doofer Wrote:  Mine's never shifted down while cruising, and I don't think it's clever enough to downshift to engine-brake if it goes too fast. If you're going downhill in 6th gear then it will coast up to whatever speed it would do if you were driving manually in 6th - it doesn't care if you go over, although this almost never happens anyway. You don't get hills steep enough on the sort of roads where you'd normally be cruising.

Mine was a generic reply to cruise and I was referring to my Mercedes which is auto ( My Peugeot Partner is manual and doesn't have cruise) and it sounds like yours is a manual.
You also say you drive on less steep hills.

I regularly tow a heavy trailer from the south coast using M3 and A34 and there are a couple of hills such as Twyford down cutting where my car will go full throttle and downshift to maintain the set speed, then at the top, just as you start to pick up speed down the other side, it downshifts to hold the speed back so you don't get the run up for the next hill. It will then have to throttle up to maintain speed for the next hill. if I look at the MPG, it's truly bad.


If I drive it without CC, I take a bit of a run up and let the speed drop off so I crest the hill at about 50mph and then let the car gather momentum down the other side to get a run up for the next hill towards the A34 turnoff. The difference in mpg is clear if I compare the two.

By keeping a more even throttle and using the stored momentum of the downhill bits to help carry me up the uphill bits I get about a 5mpg overall saving on the full journey (only this much when towing)

If the car is not towing the difference is not so noticable.
With the Berlingo being lighter and more economical to start with, I would think the differences are even less tangiable.
Either way, cruise is a nice option to have
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#10
Mine's an auto by the way, but the engine's so flexible that it almost never shifts down for a hill. It quite happily purrs up a local steep hill in 4th while set to 30mph.

Possibly arguing against myself here, I did once read a report that said that the most economical way to drive was to either not accelerate or use full acceleration. So you jab it, then coast until the speed drops a bit, then jab it again. I've never tried it, and I'm sure it would annoy the hell out of every other driver and your own passengers. But it does make me wonder whether perhaps the tiny throttle adjustments made by CC could be less efficient than the less subtle control used by any manual driver.

On the other hand, others say that CC's completely constant speed is more economical than the variation you get from manual driving.

I think it's more efficient, possibly mainly because it keeps my speed down. I can use CC at 60 in the slow lane, trundling along listening to something good, but if I drive manually then I want to overtake and speed up.
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