Does cruise control increase the mpg?

[david.aka.judas]

the reason why I ask is because, lets say you set it at 60 and you are going up and down hill.

the engine obviously accelerates up hill, but when you go down hill the car seems to brake to keep the speed constant, ie at 60.

On the other hand,

If its not set and you maintain 60 manually its obviously using the same amount of fuel going uphill, (the hill being the same hill as above), but going downhill you would take your foot off the pedal and allow the car to be subject to gravity, almost freewheeling (but not by pressing the clutch in)

With your foot off the padal, the fuel shutoff valve kicks in and saves petrol/ diesel.

so to summarise, the cruise control would save you fuel if it didn't stop the car going any faster going downhill, ie allow momentum.

[Gsi3.2]

all i can say is that i haven't noticed any difference??

[Maverick]

I havent either, I do alot of motorway miles and cruise is on nearly all the time!!

[Duncan]

There was somebody who thought the opposite (used more fuel!) in another thread - just to confuse matters! lol

I'd have though that CC would increase MPG in places like motorways etc. The CC will keep the car at the set speed more smoothly than using the pedal, and will avoid the practice of maybe slowing down (unintentionally) and then accelerating (possibly with more pedal push than needed and therefore using a bit more more fuel) - that a lot of times over a motorway journey may end up with more fuel usage, although I think we'd be talking not really that much in it.

D

[parapaul]

the engine obviously accelerates up hill, but when you go down hill the car seems to brake to keep the speed constant, ie at 60.

Mine definitely DOESN'T do that - there is no retarding force at all when going down hill.

I've got a fair sized downhill run on the way to work, on a 60mph dual carriageway, and if I have the CC on, which is pretty much always, by the time I hit the bottom, i'm doing almost 70mph.

Shame really, seeing as there's a GATSO right at the bottom!!

[ukanalyst]

Mine definitely DOESN'T do that - there is no retarding force at all when going down hill.

I've got a fair sized downhill run on the way to work, on a 60mph dual carriageway, and if I have the CC on, which is pretty much always, by the time I hit the bottom, i'm doing almost 70mph.

Shame really, seeing as there's a GATSO right at the bottom!!

Yep as Paul says CC on the Vec (and in fact all standard Cruise Control on all cars) doesn't apply the brakes, it simply decreases power. However the newer Radar Guided Cruise Control DOES apply the brakes and is designed to keep you at a set distance from the object in front and also apply the brakes rapidly if it sees the need for an emergency braking situation ... very cool but you would have to put a hell of a lot of trust in the electronics!!

[willc01]

I've noticed that with CC on you use more fuel as the CC is constanly forcing fuel through. As an example, going up a hill you would probaly use roughly the same, coming down you would use more.

The reason being, in manual mode, as you come down the hill, if you release your foot off the gas for more than 5 secs, then the fuel pump cuts out and would give you an instaneous reading of 999.99mpg. Coming down the same hill with CC on the reading would probably go to around 65mpg.

I do around 1000-1500 a week so watch fuel consumption reguarly, if youo had noticed by my other threads on this. I constantly have the trip showing on my screen as it is fairly accurate against the manual readings I take.

To summarise, yes when CC is switched on it uses more fuel or it certainly does on my long journeys and pulls my overall mpg down to around 35, where manual i can get around 42mpg.

[chrisgettings]

on some car it helps the mpg
but on others it dosnt
vw seam to do a bit less on cc
but jags get about 4 to mpg more on cc
i think it must be just what car it is

but cc does stop the 100 mph runs down the long hills
the very long drives seam a lot better with the cc

[sig63]

In my case fuel consumption is significant lower with cc on, and that is the main reason why i use it on motorways... but the reason is probably my driving style, a bit like Duncan explained above.

What i wonder is what people do with their right foot when cc is on? keep it on the floor, the pedal, the brake-pedal?
I'm still not used to it and i therefore use it only to keep moderate speed constantly (otherwise speed is going constantly upwards )

[IamtheStig]

On a run doing 75mph i lose about 3 mpg if i have the cc on - if you watch the instant consumption on the display the figures never get up to where what you can get with your right foot