It depends to what or to whom you make the comparison.
Number_Cruncher
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I've used it for 15 years in my own cars, and for ten years in US hire cars before that. It has always resulted in less fuel being consumed.
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In trying to maintain a constant speed within the engine's ability to deliver enough power (also within the single chosen gear if a manual gearbox), yes, cruise control will usually make a more efficient job of it than controlling the throttle manually to do the same thing. This is not the same as saying does one way or the other worsen fuel economy though; it I was driving for outright economy I would do so manually, bleeding speed off up hill, coasting down hill, using more appropriate gears, and so on. I would then doubtless use far less fuel than driving with Cruise Control.
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I agree fully with SjB - if you really want constant speed then the cruise control will do just that. However, I'm generally too mean to let it fuel the engine at a rate which will allow undiminished speed uphill, so I intervene at that point.
As I generally use the cruise facility as a means of avoiding speeding penalties, the option of saving fuel downhill does not generally arise when I have the thing set to the limit plus 5%.
659.
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According to the onboard computer, I usually manage to better the consumption of the cruise control. As with 659 - its by allowing my speed to tail of when going uphill. Also by observing what's coming up and allowing my speed to tail off if I'm going to be slowing soon anyway.
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According to the onboard computer, I usually manage to better the consumption of the cruise control. As with 659 - its by allowing my speed to tail off when going uphill. Also by observing what's coming up and allowing my speed to tail off if I'm going to be slowing soon anyway.
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oops - didn't mean to post twice - response on site is a little slow this afternoon.
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I remember seeing a report many years ago (Tomorrows World I think) that showed how 'fuzzy logic' could reduce the fuel consumption of a power boat on auto-pilot. It kept the craft on the same heading without adjusting the rudder at every deviation caused by a wave, thereby reducing drag created by rudder angles. Probably more accurately mimicking how a human would control it.
Perhaps the same would apply to cruise control?
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It reduces the consumption of all the cars that I've had with it. BUT the jag which is the first diesel I've had it on it doesn't make a massive difference. Mine is an Auto, but the 2.2 X Type I had it on was manual & that felt fairly weird with cruise on. You probably get used to it but in the 200 miles I did it felt very strange.
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I can always beat the cruise control for consumption.
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TourVanMan TM < Ex RF >
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I find that cruise control DOES help me save fuel - I'm not saying it's more economical though!!!
Let me explain. When I use the gas, as I'm going along the motorway, I sometimes speed up without realising it. I concentrating on the road, not the speedo as I drive. Therefore I'm actually going faster than I planned, hence using more fuel.
CC is a very relaxing way to drive in the right conditions. Likewise, I don't speed up as I'm not touching the throttle. This is what CC is for. This is why i say it IS more economical than standard driving unless you concentrate on the speedo every 10 seconds. I drive 40,000 miles a year, my heart couldn't take checking the speedo so frequently.
You pay your money, you take your choice.
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I'll be honest and say that I've not done a long distance drive in a non-CControlled car for about 10 years now, so I couldn't honestly / hand on heart say what the difference is.
But what I can say is that last week I took my 300C CRD on a 750 mile round trip to Kent, nearly entirely on CC, and at a constant CC controlled speed of either 80 or 85 mph (except for roadwork/scamera controlled sections) and I got 44 mpg from the trip. Without having concrete data to confirm/deny this, I'm fairly confident that I couldn't have got anywhere near that with my right foot acting as CC !!
MTC
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Ah, this is all very positive. Generally I cruise at an indicated 75 - but a bit less uphill and a bit more downdale, as it were. I try to control speed very finely. My 320d has cruise but I've never used it. A 500-mile round trip largely on M-ways made me think about experimenting - which I now will. But I'll be letting more significant gradients take their toll - on speed, not fuel consumption, of course.
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Yes Mad Maxy. If you drive with absolutely steady throttle opening - not too wide but certainly quite wide - you will get the best economy. That means allowing the speed to increase downhill and decrease gradually uphill. CC opens the throttle uphill to maintain speed after dragging its feet on the downgrade, like a truly carp driver (God they get up my nose on A roads those).
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