ACC and its effect on fuel consumption

[SFO]

Love the ACC on my 2022 Coast. Unfortunately, when going downhill, it drops from 7th to 6th or 5th to maintain the set speed. This really increases fuel consumption, and strains the engine. I find it really irritating.

driving without ACC results, for me, in approximately 10% better fuel economy. In non ACC mode, going downhill with foot off accelerator, the "eco" sign comes on, the revs drop to idling, and the van coasts. Speed hardly increases except on steep downhills, van feels stable and does not feel out of control. And avg mpg goes up noticeably. If only VW engineered some of this coasting function into the ACC.

am missing some setting on the ACC?

my best mpg so far

 

[kurienp]

Nope, that's how acc works, but on the flip side, using it on the motorway/a-roads does save fuel by keeping the Revs constant .

 

[Hawthorn37]

We have the same feeling, a coasting option would be good, but probably comes with safety concerns. When going down a long downhill section the braking kicks in as well, intermittently, giving a very jerky ride not good for people prone to motion sickness.

This topic has been recently discussed in this thread …

Fuel economy

Hopefully mine "loosens up" too. 40mpg was easily doable in my T5 1.9tdi manual over a long M'way trip - haven't got close to that yet in the new 150 DSG, it's more like 30mpg. Using ACC helps. Be worth setting your ACC driver assistance to ‘eco’ if not done already. I regularly get high 30’s...

vwcaliforniaclub.com

 

[RoB5urf]

Normal cruise does the same thing. If a hilly section is coming up I tend to switch it off temporarily.

 

[Sad]

Love the ACC on my 2022 Coast. Unfortunately, when going downhill, it drops from 7th to 6th or 5th to maintain the set speed. This really increases fuel consumption, and strains the engine. I find it really irritating.

Dropping the gears like that is just using the engine braking and shouldn't be causing increased fuel consumption. This isn't straining the engine, it's saving using the brakes unnecessarily.
Driving without ACC you're always likely to have a better fuel consumption as you're able to more smoothly adjust for whatever the conditions.

 

[ChunkyMonkeyDude]

I agree that it seems the ACC use gives less mpg But your stated figures are pretty good for a California in my opinion

 

[dspuk]

I have always found MPG conversations a little odd - I fill up when empty and don’t really care or think much about the in between. Of course, the fabled hypermilers do, and will switch off aircon, over inflate tyres, coast down hills and remove the back seats to get as much out of their cars as possible. I have always held the thought that the actually reality of the difference in cost monthly or annually is actually negligible. So….. I did some sums.

At 1.80 a litre (yes, I know) and assuming 8000 miles a year annual fuel costs in GBP are:

40mpg - 1,638
35mpg - 1,872
30mpg - 2,148

Given the differnce will always be about the same it effectively means that each extra 5mpg will save between 200 and 250 quid a year. Or 20 quid a month.

For that, I think I’ll just enjoy the van, drive it as I do, without huge thought of any particular way of eeking out the miles and smirk when my brother in law again asks me what my mpg is.

For some, that amount of money is well worth the hassle to semi-hypermile their Cali, and I totally respect that.

I get about 37mpg as an FYI but the engine is still a baby.

Ps - we used to use the hypermilers at Nissan to help us with electric car range testing. A fun bunch at a party.

 

[Amarillo]

I have always found MPG conversations a little odd - I fill up when empty and don’t really care or think much about the in between. Of course, the fabled hypermilers do, and will switch off aircon, over inflate tyres, coast down hills and remove the back seats to get as much out of their cars as possible. I have always held the thought that the actually reality of the difference in cost monthly or annually is actually negligible. So….. I did some sums.

At 1.80 a litre (yes, I know) and assuming 8000 miles a year annual fuel costs in GBP are:

40mpg - 1,638
35mpg - 1,872
30mpg - 2,148

Given the differnce will always be about the same it effectively means that each extra 5mpg will save between 200 and 250 quid a year. Or 20 quid a month.

For that, I think I’ll just enjoy the van, drive it as I do, without huge thought of any particular way of eeking out the miles and smirk when my brother in law again asks me what my mpg is.

For some, that amount of money is well worth the hassle to semi-hypermile their Cali, and I totally respect that.

I get about 37mpg as an FYI but the engine is still a baby.

Ps - we used to use the hypermilers at Nissan to help us with electric car range testing. A fun bunch at a party.

We do (in non pandemic years) 16,000 miles in our Cali, and one year we did 25,000 miles (the circumference of Earth at the Equator).

So by your estimations we could save £500 per annum. That is perhaps 5 family meals out for us.

I drove London to Portsmouth today , mostly on 70mph dual carriageway and motorway with ACC set no higher than 58mph. Given the heavy traffic often slowing to 40mph or less I don’t think setting ACC to 70 would have saved more than ten minutes off our 2hr 30m journey. That’s a mere 6 or 7%.

 

[Cath&Stef]

I think ACC "drives" differently to a human. A human driver lifts off the throttle when desired speed is maintained, eg downhill. DSG switches to neutral, engine drops to idle revs (on my GTE it even turns off) and vehicle coasts.
I believe that ACC never actually lifts off the throttle completely so coasting doesn't happen.
It feels like a human gives just enough accellerator to keep the vehicle moving at close to desired speed, while ACC gives it just enough not to let it slow down below the set speed. So a human lifts off and ACC never does.

 

[CarlosAAC]

I’m amazed when people post 40+Mpgin a Cali?
Just back from a 2w grand tour of Europe including several alpine passes.
2020 T6 200ps 4 motion (now 18k on clock)
2,154 miles in 56h11m
ACC set to 130kph or similar
27.8mpg

4 up with 2 kids
4 bikes on rear
Loaded with summer toys (inc SUP)
Usually 80% fresh water tank full. Guess 30% waste tank.

I think it’s reasonable for lugging around a hotel and toy garage with fully functioning kitchen and beds for 4.

I rarely see over 33mpg even when solo and lightly packed.

My view is drive it and enjoy it, was curious about MPG but frankly costs to fly across Europe provide stark contrast to any potential savings from driving at HGV speeds.

 

[Alan Andrews]

Normal cruise does the same thing. If a hilly section is coming up I tend to switch it off temporarily.

I discovered this on a recent trip up to Edinburgh.

Except that with Cruise Control, the van did not change gear even when going up long climbs on the M6 in the lake district.

Fuel range dropped from 560 to 510 very quickly when Cruise Control was enabled. I will be very wary from now on.

 

[Jim2007]

I’m amazed when people post 40+Mpgin a Cali?
Just back from a 2w grand tour of Europe including several alpine passes.
2020 T6 200ps 4 motion (now 18k on clock)
2,154 miles in 56h11m
ACC set to 130kph or similar
27.8mpg

4 up with 2 kids
4 bikes on rear
Loaded with summer toys (inc SUP)
Usually 80% fresh water tank full. Guess 30% waste tank.

I think it’s reasonable for lugging around a hotel and toy garage with fully functioning kitchen and beds for 4.

I rarely see over 33mpg even when solo and lightly packed.

My view is drive it and enjoy it, was curious about MPG but frankly costs to fly across Europe provide stark contrast to any potential savings from driving at HGV speeds.

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Same vehicle, same specs.

Our first year involved an 8000 mile trip round northern Europe, two up, plus two bikes and way too much other stuff.

We got broadly similar to the figures you’re getting.

But, there’s hope. It’s definitely got more economical as it’s got older. Now done 40000. Gone from 31.5 average over the first three years to 33mpg for the last year. All brim-to-brim figures.

And, following someone’s advice on here I started using Redex diesel cleaner in February. Gone from 33 to 35 overall. Of course £2 a litre might have subconsciously affected my driving style.

Just rolled across the Netherlands today on ACC at 100kph (the day time speed limit - not many doing it mind), getting 40.

 

[CarlosAAC]

Same vehicle, same specs.

Our first year involved an 8000 mile trip round northern Europe, two up, plus two bikes and way too much other stuff.

We got broadly similar to the figures you’re getting.

But, there’s hope. It’s definitely got more economical as it’s got older. Now done 40000. Gone from 31.5 average over the first three years to 33mpg for the last year. All brim-to-brim figures.

And, following someone’s advice on here I started using Redex diesel cleaner in February. Gone from 33 to 35 overall. Of course £2 a litre might have subconsciously affected my driving style.

Just rolled across the Netherlands today on ACC at 100kph (the day time speed limit - not many doing it mind), getting 40.

Hi Jim.

That’s reassuring, thank you for your input. I think I could see 40 if I really measured the inputs and kept under 60mph. They’re big boxes so never going to push through the air well over 75mph

 

[Hawthorn37]

On our recent trip from Rouen to just north of Toulouse (800km), 4 adults and a van with bench forward and packed to the roof, we averaged 40.5mpg. It was very busy, and had some queuing, plus N roads as well as Autoroutes. 3 drivers shared the drive, and mostly we didn’t use ACC, and kept it to equivalent of 70 mph. The return leg with slightly fewer hold ups saw 41.5 mpg. Apart from the obvious cost of fuel, it was useful to do the drive on a single tank after filling at a supermarket in Rouen on the way down, and Valence on the route north.

 

[CarlosAAC]

On our recent trip from Rouen to just north of Toulouse (800km), 4 adults and a van with bench forward and packed to the roof, we averaged 40.5mpg. It was very busy, and had some queuing, plus N roads as well as Autoroutes. 3 drivers shared the drive, and mostly we didn’t use ACC, and kept it to equivalent of 70 mph. The return leg with slightly fewer hold ups saw 41.5 mpg. Apart from the obvious cost of fuel, it was useful to do the drive on a single tank after filling at a supermarket in Rouen on the way down, and Valence on the route north.

Wow. 200ps 4motion?

 

[Hawthorn37]

Wow. 200ps 4motion?

150DSG with an 80 litre tank.

 

[SFO]

Dropping the gears like that is just using the engine braking and shouldn't be causing increased fuel consumption. This isn't straining the engine, it's saving using the brakes unnecessarily.
.

that's what I thought too .. but the "avg mpg" actually drops within a few seconds of the lower gear(s) being engaged.

my posted avg mpg is for a lightly loaded van with 2 folks. And nothing added outside.

 

[Hawthorn37]

that's what I thought too .. but the "avg mpg" actually drops within a few seconds of the lower gear(s) being engaged.

my posted avg mpg is for a lightly loaded van with 2 folks. And nothing added outside.

I’ve observed the same. However I still do use engine braking quite a bit, especially when fully loaded and coming to a stop / roundabout etc. I partly judge a good journey by not having brake dust covering the alloys!

 

[chockswahay]

I’m happy with my mpg (37 avg and 49 on the last big journey) but I am beginning to feel quite left out without being able to coast Our van is June 2020 and just will not! As for ACC I use it all the time except when going downhill then I temporarily disengage it.

 

[Jim2007]

I’m happy with my mpg (37 avg and 49 on the last big journey) but I am beginning to feel quite left out without being able to coast Our van is June 2020 and just will not! As for ACC I use it all the time except when going downhill then I temporarily disengage it.

On T6s coasting is a setting in the MFD. Don’t know about 6.1s and the digital dash.

You may already know this sorry.

 

[Amarillo]

I’m amazed when people post 40+Mpgin a Cali?
Just back from a 2w grand tour of Europe including several alpine passes.
2020 T6 200ps 4 motion (now 18k on clock)
2,154 miles in 56h11m
ACC set to 130kph or similar
27.8mpg

4 up with 2 kids
4 bikes on rear
Loaded with summer toys (inc SUP)
Usually 80% fresh water tank full. Guess 30% waste tank.

I think it’s reasonable for lugging around a hotel and toy garage with fully functioning kitchen and beds for 4.

I rarely see over 33mpg even when solo and lightly packed.

My view is drive it and enjoy it, was curious about MPG but frankly costs to fly across Europe provide stark contrast to any potential savings from driving at HGV speeds.

We’ve just returned from a 4,000 Km road trip through England, Wales, Ireland, Northern Ireland, Scotland and England again. Four refuels (one a partial refuel). Brim to brim MPG readings were 35.82 mpg (two refuels combined); 36.43 mpg and 38.43 mpg.

Pootling around London, which is more usual for us, we get high 20s.