Fuel consumption and cruise control

[Keithuk]

Neither had I until this Golf, however what I've noticed and this is what I think is happening is the diesel engine is set up to give exceptional economy,

I've mension this before on other topics about fuel con. A diesel engine is more thermal efficient than a petrol engine. For every £1 of fuel you put in a diesel car you get 35p worth of energy from that fuel whereas a petrol returns 25p of energy. Therefore diesels are more fuel efficient and do more mpg.

As for power for fuel consumption an engine that is running at its maximum torque rpm will return the maximum fuel consumption along with the the maximum power. The Golf GTD diesel has a broad torque range 1750-2500 rpm so driving anywhere in that range will give you maximum fuel con.

I've also noticed it happens when I switch on the air-con, like it drops nearly 5 mpg when its running in town.

I've also said this in the air con topics but know one believes me.

[percymon]

Well I'm still happy with my cruise control, far easier than holding my foot on the throttle for 24 miles of my 26 mile commute. I have no surges of power, but then i've not got much to start with !

Is it greedier ? - i don't know and i'm not bothered, but you'd have to do a decent enough distance at the SAME average speed to get meaningful comparison.

I put cruise to good use last week - towing another car it was great for holding a steady pace, and by watching the instantaneous mpg readout i could tell immediately when i has pulling and when on downhill sections the towed car was ever so slightly closing the gap (inches rather than feet i might add !). MPG towing at a steady 46mph on cruise - 46mpg !, would have been about 65-70mpg normally.

As for air con - i get no difference at all on or off, even in the recent hot weather.

[Chris-h]

Surely CC is not there for improving fuel consumption - it's there for convenience or comfort or keeping to the speed limit in average speed check zones!

[james_tiger_woo]

I've tested this on my Passat and on my Golf and have found that I get a better journey overall using CC than not using it. Using CC, I get consitent speed which helps economy (IMO anyway) - when I don't using it, I'm always trying to get my foot balanced "just right" to maintain 70ish which is a pain in the ****.

My commute to work is 42 miles, 35 of which is motorway - M180 and M18 at that and as these are empty and, for the most part, pretty level - CC hold me at my chosen speed which means I'm not contantly speeding up and slowing down.

Rurally, however, it is pretty much useless as country roads don't lend themselves to "one speed" very much.

It helps me as it means that it's one less thing to worry about: I'm driving at one speed so I don't have to worry about that - which leaves more time for me to read my book, have a sandwich, have my cup of tea, stretch out, have a short kip - all while the car drives for me

Seriously though - it helps me and I like it as, driving 25-30k a year, it seems to help my economy which can only be good for my wallet. It suits me, but it might not suit everyone - it's all very subjective.

[p3asa]

I may have been miss-informed on this, but I read somewhere not to even bother to use the cruise control for at least the first 5000 miles.

Maybe more to do with running it in, as you need to alter the revs and the best way to do this is to change gear. But certainly not for 5000 miles

As for fuel economy, I've found I get more MPG using my foot and reading the road compared to cruise control. Using my feet to drive doesn't bother me or I would have got DSG and use CC at every opportunity

[HHGTTG]

CC is alright for keeping speed to legal limits but I certainly don't think that taken overall it improves fuel economy. I know that after over 55 years of driving I can with my right foot relaxing pressure on the accelerator and using the car's momentum achieve better mpg. However this still doesn't really explaing why I don't achieve VWs combined mpg!!

[AxeMurderer]

My limited experience (~170K) also suggests that I get better economy without cruise control - it broke in my old A6 and I managed more miles per tank afterwards. I've not yet compared it on the Golf.

[andyCYM]

Not really the point of the thread I know, but I think drivers using cruise control in traffic are a nuisance and a potential danger - for example, not accelerating into gaps or not increasing speed slightly when overtaking to get past a car in the insde line that clearly needs to move out to pass slower traffic. My guess is that a lot of these drivers have set the cc and don't want to or can't be bothered to disturb it.

May be this is why it's banned in Belguim (I think)?

p.s. This is not sour grapes cos my GTD doesn't have cc & I was too mean to spec it, honest.

[Ezpatman]

In my experience on motorways it is the constantly changing speed of non cc cars that is the cause of so many problems. Drivers without cc tend to speed up going downhill and slow down going up hill. This results in the gap between cars continually closing down - requiring braking to reestablish a safe gap, which in turn means the driver behind has to slow down and then you get the domino effect and slow bunched traffic! With cc everyone retains a safe gap uphill and down with no need to brake or accelerate so avoiding bunching.
I lived for many years in the USA where everyone uses cc on the freeways and basically even on very busy freeways (I95) you could set your cc and cruse for hours as everyone maintained their speed - including trucks which could keep up with the traffic and so avoid the "slow overtake" we live with in the UK that reduces miles of motorways to one lane roads.
Use cc and make roads safer.
To be contentious it is the same problem with manual v automatic cars - why on earth anyone would want a manual car in traffic infested UK is beyond me - clutch up, down, up, down till your left leg aches!!! Why??????

[SC03OTT]

I'm not paying the premium for an auto is my reason. But then traffic is not really that bad north of the border when you compare it to the like of London and other major English cities.