MPG with C/Control on

[glojo]

Glojo, is this an extract from your own manual or did you pick it up from the current on-line manual (is your S211 a face lift model)?

I simply went on-line, logged onto the Mercedes-Benz home site and then accessed their manuals.

My quotes are an EXACT extract and it appears they have simply added a little more information when compared to our older manuals

Cruise control lever

You can operate cruise control and variable Speedtronic with the cruise control lever.
The LIM indicator lamp on the cruise control lever indicates which system you have selected:

• LIM indicator lamp off:
  cruise control is selected
• LIM indicator lamp lit:
  variable Speedtronic is selected

To store the current speed or a higher speed

LIM indicator lamp

To select the current or last stored speed

To store the current speed or a lower speed

To switch between cruise control and variable Speedtronic

Deactivating cruise control
Selecting cruise control

Check whether LIM indicator lamp

is off.
If it is off, cruise control is already selected.
If it is not, press the cruise control lever in the direction of arrow

.
LIM indicator lamp

in the cruise control lever goes out. Cruise control is selected.

Storing and maintaining the current speed

You can store the current speed if you are driving faster than 30 km/h and ESP® is activated more.

Accelerate the vehicle to the desired speed.

Briefly press the cruise control lever up

or down

.

Remove your foot from the accelerator pedal.
Cruise control is activated. The vehicle automatically maintains the stored speed.

Cruise control may be unable to maintain the stored speed on uphill gradients. The stored speed is resumed when the gradient evens out. Cruise control maintains the stored speed on downhill gradients by automatically applying the brakes.
Vehicles with manual transmission:

• Always drive at adequate, but not excessive, engine speeds.
• Change gear in good time.
• If possible, do not change down several gears at a time.

Selecting the current or last stored speed

If it stays at 2000rpm whilst freewheeling then I'd suggest that the whole cruise control economy issue is a bit of a moot point & you need the engine looked at. Wouldn't it drop to 800rpm or thereabouts?

Thankfully the engineers among us understood where I was coming from and answered my queries in a language even I could understand and note that I thank them

The pages from the latest manuals are quite clear and far be it for me to disagree with them.

Regards
John

 

[hawk20]

Assuming the translation to English is correct on the MB website (which seems likely) glojo's excellent detective work suggests that cruise can apply the brakes if needed and does do so. (Contrary to years of postings on this and other forums) Well done John.

Now some queries. Does this apply only to current cars? I have owned numerous Mercedes in the past that went way over the set cruise control speed when going downhill and which appeared to me to be only using engine braking?

Secondly, I don't think the use of brakes would occur much if at all on most motorways as the inclines are shallow enough that in general engine braking would be enough to keep the speed at 70. So even if brakes are used in extremis that does not really affect the arguments about which is most economic at achieving a steady cruising speed. BTW if cruise needs to apply brakes to keep the speed to 70 mph (and engine braking is not sufficient) then a good driver would need to apply brakes as well. (Unless we want to be one of those annoying creatures who keep speeding up and then slowing down as the incline changes). (That would also involve exceeding the speed limit, of course, if cruising at the limit).

 

[Diesel Benz]

Assuming the translation to English is correct on the MB website (which seems likely) glojo's excellent detective work suggests that cruise can apply the brakes if needed and does do so. (Contrary to years of postings on this and other forums) Well done John.

Now some queries. Does this apply only to current cars? I have owned numerous Mercedes in the past that went way over the set cruise control speed when going downhill and which appeared to me to be only using engine braking?

Secondly, I don't think the use of brakes would occur much if at all on most motorways as the inclines are shallow enough that in general engine braking would be enough to keep the speed at 70. So even if brakes are used in extremis that does not really affect the arguments about which is most economic at achieving a steady cruising speed. BTW if cruise needs to apply brakes to keep the speed to 70 mph (and engine braking is not sufficient) then a good driver would need to apply brakes as well. (Unless we want to be one of those annoying creatures who keep speeding up and then slowing down as the incline changes). (That would also involve exceeding the speed limit, of course, if cruising at the limit).

The capability for the car to autonomously apply brakes did not exist until SBC and Distronic Plus (I understand W220 with Distronic also can apply brakes but I'm not sure). So far I've understood that the SBC based W211 does not apply brakes but the face lift version would (someone else posted this but I'm not sure if it is based on the info at the manual or something else). The manual text was well spotted by glojo, I had not noticed the change while often browsing the on-line manual.

The W221 user manual has the same text as the new W211 manual. Although translation errors are not rare, I believe this one is not an error when it appears the same for two cars.

It is easy to detect that the car anyway is using engine braking, even our roads allow testing this. I've never tried on a gradient where brakes would be needed. Testing would be interesting already to figure out high high engine RPM the car would make use of for engine braking before applying brakes.

I'd still be happy to see pointers to WIS documents or similar on the subject. If/since the implementation has been changed recently, WIS should describe it. I did not find it for W211, nor for W221 but I may have looked at the wrong place.

 

[glojo]

We are only really talking about whether cruise control is more economical or as economical as normal driving, but we keep throwing in red herrings that side track us. I say 'we' because I am as guilty as anyone.

Forget the 70mph speed as once more that is a red herring to what we are discussing. We are not discussing clinical, or laboratory conditions, we are discussing everyday use.

We are discussing cruising, not religiously sticking at the EXACT speed as I would respectfully suggest that even cruise control cannot do this under generalised road conditions (winds, cross winds, undulations etc etc.

Put cruise control at 60mph and that is what you get, uphill and down dale the unit will take the strain out of the foot and try to keep the speed at approximately 60mph. The driver that is using his foot coupled to his brain will take advantage of any given situation and if there is a downhill gradient that allows the car to increase speed with the foot completely off the accelerator, then so be it, providing it is safe, providing it is not breaking any speed limit then so what? The driver will still want to cruise at 60 mph but by allowing the car to gain momentum which we might describe as freewheeling then no harm done, no laws are broken the car has not been put in neutral and there has been a saving. Likewise if there is a slight gradient, the cruise control is not subtle about increasing the rpm to maintain the car at 60mph, whereas Joe the plumber will perhaps decide so what? There is a downhill gradient coming up and I know the car will gain momentum the other side. Both of us will complete the journey at an average speed of 60mph but one of us will have used less fuel.

I note how we have all of a sudden linked the braking to cars fitted with SBC?? Has the C-class got this feature because one of my extracts is from the C-class manual? It would be wrong to try and twist the facts and blame it on translation, we could say that about any text. BUT..... I am still interested to hear from anyone willing to try this test and I think it would help resolve these contentious issues.

Travel down a hill at 60mph in top gear.

Lift your foot off the throttle and note how quickly the car slows down without touching any controls

At the same location do the exact same thing but this time when you lift your foot off the throttle engage the cruise control but make sure it has previously been set to 40 or 50mph.

Does the car slow quicker?

That to me is the nitty gritty as both procedures should in theory be the same unless cruise control uses either the brakes or changes down and uses engine braking.

I want to be in charge of my braking, be that engine braking, retardation by changing down or whatever combination we care to suggest.

Regards
John

 

[st4]

I want to be in charge of my braking, be that engine braking, retardation by changing down or whatever combination we care to suggest.

Regards
John

I also want to be in full control of the throttle too Hence my disregard for CC

I think, in my case anyway, having full control over the car allows one to concentrate more on the business of driving.

 

[raymont]

If I reduce the speed limiter on my car whilst travelling at the limited speed , say from 60 to 40, the car seems to use both the gears ( by changing down) and the brakes ( have a slight squeak at the moment and I can hear it) to effect the speed reduction. It does it quite aggressively.

Don't know how it works with CC. I'm going out in a bit so might have a chance to try it.

 

[Mr E]

I also want to be in full control of the throttle too Hence my disregard for CC

I think, in my case anyway, having full control over the car allows one to concentrate more on the business of driving.

I have an issue with this assumption - I used CC a lot, I have full control over the car. I can choose when to use it, I can accelerate and brake as required.

I'm also able to concentrate on driving more as I'm nor worried about the speed creeping up

 

[st4]

I have an issue with this assumption - I used CC a lot, I have full control over the car. I can choose when to use it, I can accelerate and brake as required.

I'm also able to concentrate on driving more as I'm nor worried about the speed creeping up

Everyone is different, I find that my concentration lapses with CC on as I am less engaged with driving my car.

 

[sweeper]

Useful in Europe too. Much less traffic on motorways in France and can go ages at constant speed. Helps avoid fines!

I use cruise every day. Love it. I use it in speed limit areas when there is not much traffic. So easy to keep to a chosen safe speed without speedo watching. Good safety feature, used properly, IMO.

The limiter can be useful for speed limits too. And some prefer that.

That has got to be the most dangerous use of cc, speed limiter is there for avoiding going above the speed limit, cc is there for open stretches of motorway with virtually no traffic, i find it rarely of any use in the uk, speed limiter is a good option and i do use it, cruise i did use on part of our journey to South of France in June, mainly becuase i have been suffering with a painfull knee and this helped, i even set it just below 100mph for one stint, one thing i did notice on the long hauls up the mountains, is that the gearbox let the torque converter go (ie more slip) to maintain steady speed without going down a gear, i have never noticed this when driving without cc, suggesting to me that i would have used more throttle up the hill than the cc did, i also find cc doesn't accellerate on resume as fast as i would normally. Hence i found fuel consumption no different than normal driving, so i would say it depends on driving style, if you tend to worry about fuel consumption, you will probably find cc uses more if you "drive" your car you'll probably find it the same or better.

 

[glojo]

Everyone is different, I find that my concentration lapses with CC on as I am less engaged with driving my car.

I'm with Mr E and Cruise Control is an excellent aid which takes the strain out of driving, I was simply saying that I don't mind slightly going over a set speed if it is safe, legal and econimical to do so Unless we live in the eat of the country I don't suppose there are many roads that remain flat and level for any length. Here in the West country we are either at the top of a hill, the middle or the bottom of one. If we are at the bottom of a hill, then it will not be for very long.

If we are travelling long distances on motorways then I fully understand why folks elect to use Cruise Control, I fully understand and go along with the reasons. NO WAY am I arguing against the use of this excellent feature and it is without doubt down to choice.

My driver always uses it

Regards
John

 

[sweeper]

Soooo, (and, like John, genuine question here)
On my way to work in the morning there is a long downhill stretch where I can take the car out of gear and coast, while keeping up a safe speed (manual car).
Will I use more petrol doing this or staying in gear on a whisper of throttle and frequent times on overrun?
Ditto the above when coming off on a slip road - do I coast in neutral to the give way sign or just back off the throttle?
And last of all, to be most fuel efficient, do I let the engine run freely a 40mph in fourth, or labour slightly in fifth?
TIA.

Don't coast out of gear, the engine is then using fuel to keep idling, keep in a higher gear as possible, at 40 keep in 4th, not as much for fuel economy but load on the engine, labouring puts a high load on bottom end, coasting out of gear would also be dangerous as the car will not behave in a stable manner when cornering if it is not being driven.

 

[oldcro]

Don't coast out of gear, the engine is then using fuel to keep idling, keep in a higher gear as possible, at 40 keep in 4th, not as much for fuel economy but load on the engine, labouring puts a high load on bottom end, coasting out of gear would also be dangerous as the car will not behave in a stable manner when cornering if it is not being driven.

I always thought coasting in neutral was illegal.

 

[Dryce]

So far I've understood that the SBC based W211 does not apply brakes but the face lift version would (someone else posted this but I'm not sure if it is based on the info at the manual or something else).

I have a non-facelift W211. I believe it uses the brakes.

Simple test. Long downhill incline with CC engaged speed doesn't rise. Same incline without CC and foot off accelerator speed does rise. CC doesn't change down a gear.

So it must be braking.

 

[Dryce]

I also want to be in full control of the throttle too Hence my disregard for CC

I think, in my case anyway, having full control over the car allows one to concentrate more on the business of driving.

Psssst .... you have a W211. The only thing you actually control directly is the steering. The accelerator and brakes are bother computer controlled.

 

[Dryce]

That has got to be the most dangerous use of cc, speed limiter is there for avoiding going above the speed limit,

Most dangerous use of CC?

 

[Diesel Benz]

I have a non-facelift W211. I believe it uses the brakes.

Simple test. Long downhill incline with CC engaged speed doesn't rise. Same incline without CC and foot off accelerator speed does rise. CC doesn't change down a gear.

So it must be braking.

This sounds strange because my car definitely shifts down when driven downhill with CC, not if I don't have CC on. One should look at the brake lights (the third one), if it brakes, the brake lights would come on. It just isn't easy for the driver to see even the third brake light (at night one might see the brake lights illuminating the road behind the car).

Your car seems to be a gasser, I would not expect this bringing a difference but never know. Is the engine idling when it brakes?

 

[glojo]

This sounds strange because my car definitely shifts down when driven downhill with CC, not if I don't have CC on. One should look at the brake lights (the third one), if it brakes, the brake lights would come on. It just isn't easy for the driver to see even the third brake light (at night one might see the brake lights illuminating the road behind the car).

Your car seems to be a gasser, I would not expect this bringing a difference but never know. Is the engine idling when it brakes?

Another question

Can the brakes be activated without the brake lights being illuminated.

I do n t have any experience of newer vehicles and the most modern of technology.

Regards
John

 

[Dryce]

Your car seems to be a gasser, I would not expect this bringing a difference but never know. Is the engine idling when it brakes?

The engine speed is well above idle. A bit over 2000RPM. Going down a motorway incline at 50. The difference without CC is the speed will gradually rise.

Maybe it depends on the amount of braking required and speed.

 

[Diesel Benz]

The engine speed is well above idle. A bit over 2000RPM. Going down a motorway incline at 50. The difference without CC is the speed will gradually rise.

Maybe it depends on the amount of braking required and speed.

A pure guess but someone mentioned how the gasser opens the throttle valve when the injection is closed and the engine driven by the car speed on downhill, to reduce engine braking. The difference could (partially?) come from the ECU adjusting the throttle valve and then adjusting the engine braking force as necessary? I'll try to spend some time doing home work on this subject, would be nice if someone who has done it already would give accurate pointers.

 

[Diesel Benz]

Another question

Can the brakes be activated without the brake lights being illuminated.

I do n t have any experience of newer vehicles and the most modern of technology.

Regards
John

On the face lift W211 as well as on the W221 the car brakes with the brake pedal itself (or when it brakes, the brake pedal physically moves) and the brake lights come on already from the brake light switch.

SBC is different because the car can brake without moving the pedal (at brake hold the brake pedal is in idle position, but brake lights still come on). Theoretically the car could brake without brake lights coming on but I'm pretty sure lights would come on if/when the car brakes when asked by CC, also on an SBC car.