Fuel Economy - Cruise Control VS Limiter

[craig_c]

i have been trying out my fuel economy of my w210 e320 cdi. I use the 22mile trip to my girlfriends house as the test for my car.

I seem to be finding that if i use the limiter on the way theyre, rather than the cruise control i get better MPG. My theory is that the limiter allows me to back off naturally down steep hills where as the cruise control sometimes struggles.

its mainly 60mph dual carriageway and i see about 34mpg. 2 or 3 more than when i use cruise control.

does anybody else find this?

 

[rf065]

My theory is that the limiter allows me to back off naturally down steep hills where as the cruise control sometimes struggles.

does anybody else find this?

I find cruise control wastes fuel when you are travelling up hill as it has no concept of saving fuel, only maintaining a set speed regardless of how much fuel is used. Tight bends are another area cruise will use fuel when the natural reaction of the car is to scrub some speed off due to the increase in friction/load.

Russ

 

[turbopete]

ive never tried mine with the limiter. went to stafford and back with the air con set to economy mode, cruise control set to 70mph. filled up at start and end of my return trip. i worked it out (4.54 litres to a gallon) that the old beast returned 39.2mpg! not bad considering it get air in the fuel and has 140k on the clock!

 

[television]

This all depends on how you drive the car,if you go speeding onto the motorway and use the CC, then the car will change gear and accelerate up hills, if you go onto the motorway in a more leisurely manner the car will not accelerate to get back up to speed.

This is all because the engine ECU talks to the gear box ECU and it short term memorizes the way the car is driven.

 

[DougCLK320]

I agree with Russ and have noticed inferior fuel consumption when cruise control is used.
Doug

 

[turbopete]

mabe im gonna have to give this a try next time i go any distance then! especially as fuel is going up again!

 

[djb]

I also experiance the same as the OP.

Another reason the figs on speed limiter is better, is due to the ave speed is probably lower than CC, due to some lifting off.

 

[simon_wall69]

This all depends on how you drive the car,if you go speeding onto the motorway and use the CC, then the car will change gear and accelerate up hills, if you go onto the motorway in a more leisurely manner the car will not accelerate to get back up to speed.

This is all because the engine ECU talks to the gear box ECU and it short term memorizes the way the car is driven.

The cruise control on both of mine (123 and 124) seems to floor the throttle when I tell it to speed back up to the set speed - I suppose due to the fact that the systems are much older and it doesn't have the electrics.

How do these older systems work?

 

[Blobcat]

In our Caravelle I can improve the fuel economy by ~1mpg by not using cruise. In my 320 and previous one whilst I could get an improvement I didn't see enough benefit to outweigh the convenience. I do knock cruise off and very rarely brake on motorways so still drive the car just use the cruise stalk instead of the accelerator.

 

[Number_Cruncher]

The problem with these comparisons is that apples are being compared to oranges.

If cruise control is applying more throttle than you would in a given situation, that means that cruise control is getting you to your final destination faster. So, yes, I'm sure you can beat the economy of cruise control, but, you would be slower for having done so.

 

[television]

The cruise control on both of mine (123 and 124) seems to floor the throttle when I tell it to speed back up to the set speed - I suppose due to the fact that the systems are much older and it doesn't have the electrics.

How do these older systems work?

The 772.3,4,5 do not have an ECU that talks to the engine, so these cars cannot remember your driving style, the 722.6 boxes will.

We heard of a guy who used CC on the motorway in the rain after he had been driving hard and fast, when he engaged resume, the wheels spun driving him into the central reservation.

If he had entered the motorway in a slower manner the car would have gently resumed without changing down, as the car would have know that he was driving in a leisurely manner

 

[Parrot of Doom]

I use the cruise control on long motorway trips (well anytime I can really), but frankly I've never noticed a difference. I think because I tend to keep my speed exactly the same on climbs, whereas many other drivers just slow down slightly. If I stick to around 70mph I tend to get very near 40mpg. If I was doing 60 I'd easily beat that.

If the cruise control does use more fuel, its a cost I'm happy to pay as with it I always feel much more relaxed after a trip than I would without.

 

[rf065]

The problem with these comparisons is that apples are being compared to oranges.

If cruise control is applying more throttle than you would in a given situation, that means that cruise control is getting you to your final destination faster. So, yes, I'm sure you can beat the economy of cruise control, but, you would be slower for having done so.

I think if you put that to the test, the difference between the two cars could be measured in seconds rather than minutes. MPG however could have a wider margin making it worthwhile for some.

Russ

 

[alindsay81]

The 772.3,4,5 do not have an ECU that talks to the engine, so these cars cannot remember your driving style, the 722.6 boxes will.

We heard of a guy who used CC on the motorway in the rain after he had been driving hard and fast, when he engaged resume, the wheels spun driving him into the central reservation.

If he had entered the motorway in a slower manner the car would have gently resumed without changing down, as the car would have know that he was driving in a leisurely manner

How long does its 'memory' last ? Will it remember the last 5 minutes of driving style or is it reset on start like the 'from start' mpg etc

 

[Jack the Lad]

I agree with the OP about the better fuel economy with the speed limiter than with cruise control or neither. On my regular commute it is around 10% better mpg, but no slower.

The other thing I like about using the speed limiter is that it is so relaxing to drive and much more relaxing than CC if there is any appreciable amount of traffic about. Just set it to the speed limit and drive normally.

There's none of the frequent cancelling and resuming or fiddling with the set speed to get it 'just right'. You also avoid those situations where you hold off and hold off cancelling the CC as you wait for some middle lane hog to creep past so you can pull out and suddenly find yourself approaching that truck in front quicker than you thought and nowhere to go. Another one is where you've set the CC in say a 30 limit, accelerate up to a higher speed when it ends, and miles later when you approach some lights or a roundabout and lift off, the car doesn't slow down past 30mph as the CC kicks back in and you end up late braking.

 

[The Rock]

Jack the Lad you've been reading my mind. You'v decribed my experience perfectly. I love the speed limiter, albeit that you do need to watch CC and SL when descending, especially near speed cameras.
I've found that with CC engaged in, say, a 30, if you descend a steep hill the car will reach 35 or more before changing down, sometimes too much to the point that you're revving yer nuts off. I've even had the CC disengage automatically under those conditions.

Rock

 

[television]

How long does its 'memory' last ? Will it remember the last 5 minutes of driving style or is it reset on start like the 'from start' mpg etc

Its fast if you change your driving style, ie if you have been overtaking and kicking down, and hit a 30 MPH limit and stop kicking down it goes back to normal and memory cleared in no time, it has to if you think about it

 

[jimsinessex]

Jack the Lad you've been reading my mind. You'v decribed my experience perfectly. I love the speed limiter, albeit that you do need to watch CC and SL when descending, especially near speed cameras.
I've found that with CC engaged in, say, a 30, if you descend a steep hill the car will reach 35 or more before changing down, sometimes too much to the point that you're revving yer nuts off. I've even had the CC disengage automatically under those conditions.

Rock

I have now had the chance to compare the CC and SL on my previous 1999 CLK + 722.6 trans with the current 2008 CLK + 7G trans and where the old car would overrun on down slopes by 2/3 mph the new car has no detectable overrun at all even on the steeper slopes.

On the new car there is a noticeble dip of the brake pedal if the SL is engaged at a speed slightly above the setpoint suggesting the brakes are used for control as well as the engine management. I did not notice this happening on the old car.

The new car is a 320CDI diesel and the old was a petrol 230K but I can't see that is a factor.

Jim

 

[turbopete]

The 772.3,4,5 do not have an ECU that talks to the engine, so these cars cannot remember your driving style, the 722.6 boxes will.

We heard of a guy who used CC on the motorway in the rain after he had been driving hard and fast, when he engaged resume, the wheels spun driving him into the central reservation.

If he had entered the motorway in a slower manner the car would have gently resumed without changing down, as the car would have know that he was driving in a leisurely manner

so how does that work with manual cars Malcolm? im guessing they dont have any kind of memory like the auto cars do? dads always seems to floor it up to speed then hold steady. a w203 220cdi manual 6 speed. im curious, thats all!

 

[television]

so how does that work with manual cars Malcolm? im guessing they dont have any kind of memory like the auto cars do? dads always seems to floor it up to speed then hold steady. a w203 220cdi manual 6 speed. im curious, thats all!

No it cannot work with a manual car this way at all, on autos they will go down a gear to regain the CC set speed, and a manual one cannot, so on an incline you have to change gear if the engine is struggling