Cruise Control MPG

[Mr Wolf]

I use cruise control on all my longer motorway journeys as I find it relaxing and comfortable. As I'm rarely in a hurry, I usually set it at about 60 mph so I don't have lorries overtaking me (nor do I overtake many other vehicles!) However, when going up steeper inclines I drop down to 5th gear if the engine starts to labour. On longer downhill stretches I switch cruise control off and coast until speed is reduced to 60 mph, and then switch it back on again. By using this approach I can obtain an indicated 50 - 55 mpg. Would I get better mpg by not using cruise control, or using it differently?

[Duggerz]

I understand that coasting doesn't have much of a benefit with modern engines because they shut off the fuel during overrun, whereas idling uses a small amount of fuel. Of course there is internal resistance of the engine parts to overcome in overrun so really I think it's a wash. Plus is coasting even legal? I'd be interested in your figures though if you have a back to beck comparison.

[Konrad C]

I went to NEC for the Photography Show last Sunday, and used less fuel (bars) compared to similar trips to the same venue. I did not use cruise control at this time. On the way back on the M40 got held up due to a crash. I did over 250 miles to the half way point on the fuel gauge. I got over 100 miles more and still had a couple of bars. The journey includes travelling through London, so fuel consumption would be better, adding being stuck on the M40 traffic.

Mickey (Mr Wolf), you say you had to change down to 5th, you have to turn off the cruise control? With my car, the engine will over rev unless CC is turn off prior the changing gear. My clutch is due for a change!   

 

[Mr Wolf]

Quote

I understand that coasting doesn't have much of a benefit with modern engines because they shut off the fuel during overrun, whereas idling uses a small amount of fuel. Of course there is internal resistance of the engine parts to overcome in overrun so really I think it's a wash. Plus is coasting even legal? I'd be interested in your figures though if you have a back to beck comparison.

When I said coasting I meant leaving the car in gear and allowing the car's momentum take me down the hills. I assume this is what you call overrun? I do not believe that what I do is illegal? The advantage in my 'coasting' down hills is that I travel faster and therefore further than if cruise control is on, as it will limit the downhill speed and therefore decrease the momentum when reaching the flat. I assume both would use the same amount of fuel.

I often drive with the current mpg screen on. It I try to maintain speed uphill by increasing power the indicator shows a decrease in indicative mpg whereas using no throttle downhill (or at any time!) increases mpg. I tend to use the throttle very sparingly but without impeding the progress of other motorists and get a kick out of getting good mpg figures. Today a did a 45 miles return trip with a 15/85% mix of town/dual carriage way driving and achieved an indicative 52.7 mpg. I'll be holidaying in Yorkshire in May and will do a brim to brim test which is the only real measure of mpg.

[Konrad C]

I too use a very light foot on the motorway. I have my foot off the throttle downhill, and use more throttle uphill. I believe that the CC tries to maintain speed and uses more fuel. Due to the engine being valvematic, it seems to be easy to roll  without loosing to much speed., unlike diesels. I drive around 70 mph most of the time, where clear.     

[Husbandofstinky]

I have picked up over the years from various sources that CC does use more fuel. In a nutshell it is because it is reactionary and can't plan ahead as you do to road and traffic conditions.

A quick scan and this was picked up by the RAC amongst others

http://www.rac.co.uk/drive/advice/driving-advice/fuel-saving-tips/

Quite simply you and your right foot will do a better job ultimately. Just need to keep an eye on the speed.

[Anthony Poli]

It's like swings and roundabouts when using cc, if your lazy like me, then cc works well enough without knocking it off and I'm not doing bad with my mpg. Without it I can do better, but you sacrifice comfort on long journeys. 

Using techniques like pulse and glide will improve things. I would definitely recommend checking your tyre pressures, you don't need to loose much air to have a dent in your mpg. I have the tyre pressures set for motorway driving all the time, but still nothing can help when it comes to being in traffic that is going nowhere fast.

 

 

[Duggerz]

Although the Oxford dictionary defines coasting as the easy movement of a vehicle without the use of power, I've most often heard it used when referring to travelling downhill with the gears in neutral. The later I think is a no no. I remember a top gear episode where JC drove a big car and discovered that for best economy take a very gradual run at the hills and coast down the other side. He managed something like 39mpg from a 4.2l Audi A8.

[Heidfirst]

16 hours ago, Husbandofstinky said:

I have picked up over the years from various sources that CC does use more fuel. In a nutshell it is because it is reactionary and can't plan ahead as you do to road and traffic conditions.

This, albeit there are CC systems existing & coming that use satnav data to plan for up & down grades & act appropriately.

[Alan1234]

I did a brim to empty test to Doncaster drove around a few days and came back to reading . On the 50 limit section it was giving the best mpg 60 mpg on cruise control for 30 odd miles .56 mpg at 65 no cruise 

[cheesvo]

On 28/03/2017 at 8:41 PM, Mr Wolf said:

However, when going up steeper inclines I drop down to 5th gear if the engine starts to labour

I guess you're driving a diesel. I usually use 6th gear only when I'm traveling faster than 70mph. Have a try with 5th at 60mph to see if you can get any better mpg. 

I get 70+ mpg in 6th gear at 80-90mph. I usually keep my rev at 2-2.5k rpm. 

[Heidfirst]

2 hours ago, cheesvo said:

I get 70+ mpg in 6th gear at 80-90mph. I usually keep my rev at 2-2.5k rpm. 

Sorry, don't believe it unless you are going downhill or lifting off. The T25 & T27 show current fuel consumption differently - the T27 doesn't have the instantaneous figure readout like the T25 (plus I suspect that the T27 is a more accurate system).

 

p.s. welcome to the forum 

[cheesvo]

2 hours ago, Heidfirst said:

Sorry, don't believe it unless you are going downhill or lifting off. The T25 & T27 show current fuel consumption differently - the T27 doesn't have the instantaneous figure readout like the T25 (plus I suspect that the T27 is a more accurate system).

 

p.s. welcome to the forum 

Hah, I wish I could take a picture of that as proof. But I guess the traffic was much better on that particular day as that was my highest record. 

And thanks. Been snooping for a year without actually posting anything :D

[Anthony Poli]

Sorry, don't believe it unless you are going downhill or lifting off. The T25 & T27 show current fuel consumption differently - the T27 doesn't have the instantaneous figure readout like the T25 (plus I suspect that the T27 is a more accurate system).

 

p.s. welcome to the forum 

Hah, I wish I could take a picture of that as proof. But I guess the traffic was much better on that particular day as that was my highest record. 

And thanks. Been snooping for a year without actually posting anything :D

 

 

 

I was the same ;-)

 

 

Sent from my iPhone using Tapatalk

[Alan1234]

Wow your right using your driving style I can get 79mpg 👍

[Mr Wolf]

6 hours ago, cheesvo said:

I guess you're driving a diesel. I usually use 6th gear only when I'm traveling faster than 70mph. Have a try with 5th at 60mph to see if you can get any better mpg. 

I get 70+ mpg in 6th gear at 80-90mph. I usually keep my rev at 2-2.5k rpm. 

As it says alongside my post - I'm driving a 1.8 petrol (not a diesel).

With economy in mind, my car indicates when it thinks I should change gear up or down. When my speedometer is showing just over 30mph in 4th, the indicator suggests I change up to 5th, and when it shows just over 40mph it suggests I change up to 6th. This is supposed to help obtain best fuel economy and is contrary to your advice where you use 5th gear until you reach 70mph.

If you're getting 70+ mpg in 6th gear at 90mpg then you must be getting about 100mpg at 50mph. Suggest there might be something wrong with your mpg indicator.

Thanks for your input but I think I'll continue to drive as I do

[Duggerz]

Cheesvo, thanks for posting, this is very interesting! Would you be willing to run an experiment? Really the only way to get accurate figures is to bring the tank, more the mileage, brim again and calculate. Would you be willing to do that for us to test your hypothesis? I for one would be very keen to see these results.

[cheesvo]

3 hours ago, Duggerz said:

Cheesvo, thanks for posting, this is very interesting! Would you be willing to run an experiment? Really the only way to get accurate figures is to bring the tank, more the mileage, brim again and calculate. Would you be willing to do that for us to test your hypothesis? I for one would be very keen to see these results.

I'm testing this myself at the moment. Changing from a petrol, that is the one difference I notice. I think up shifting  to the highest gear as fast as possible isn't the economical case for diesel.

However, with mixed driving, it is hard to achieve this figure. That time I filled up at the service station on the way from Wakefield to Sheffield, reset the mpg indicator, then continue on M1 for another 10 miles. When I made the turn at J33 to Sheffield, my mpg indicator showed 70.5.

4 hours ago, Mr Wolf said:

If you're getting 70+ mpg in 6th gear at 90mpg then you must be getting about 100mpg at 50mph. Suggest there might be something wrong with your mpg indicator.

Strangely though, as Mr Wolf said, when in 5th and 2-2.5k rpm, my mpg doesn't go up significantly. It just doesn't drop as fast as if I was in 6th and 1.8k rpm.

And my post earlier applies to my diesel engine, so in your case, it's not applicable. It's already pretty good mpg for a petrol. My Corolla T Sport 1.8 couldn't get that much. 

[Heidfirst]

13 hours ago, cheesvo said:

Strangely though, as Mr Wolf said, when in 5th and 2-2.5k rpm, my mpg doesn't go up significantly. It just doesn't drop as fast as if I was in 6th and 1.8k rpm.. 

You aren't doing 80-90mph at those rpm though. Iirc on my T27 (& I doubt the gearing is much different on the T25 2.2) 2500rpm in 6th = an indicated 80mph (true ~74/75).

I know that it is possible to get 70mpg out of a 2.2 Avensis  - I have managed it once on a journey like yours that was pretty much straight onto dual carriageway/motorway & straight off again but I wasn't doing 80/90mph. & your T180 is generally thirstier than my 150.

[Alan1234]

Ok enough is enough with this jokey thread about getting 70-80 etc mpg it's impossible at those speeds or with your car the max you will ever see is 50-60mpg at around 50-60 mph on a flat road I did a brim to empty test on my t27  2.2 with photos to prove yes I could get the gauge to read 99 mpg for about 10 sec with no throttle input . So stop your joking or delusional talk  . Speed = wind pressure Against your car every 10mph over 50 takes a lot more juice to push your car through the air .

[Heidfirst]

1 hour ago, Alan1234 said:

Speed = wind pressure Against your car every 10mph over 50 takes a lot more juice to push your car through the air .

Drag increases with velocity squared.