To cruise or not to cruise

I don't imagine the figures would be all that significant either way, however I would assume that using Cruise would most likely save on fuel since it's monitoring/managing the speed.

Mind you, it likely depends a lot on the terrain, weather, etc... as well as the speed you're cruising at.

Your owner's manual indicates that you should use the 'E' (Economy) setting whilst in Cruise, rather than the 'S' (Sport) mode.

I *love* cruise. Mind you, we also have rather straight highways 'round here. I wouldn't necessarily use it, say, in Ireland! ;)

Yours,

Allan

... and Andy Mann spake, saying:

In general, probably... If you really try, by using you foot to control the throttle you can do better then cruise control can. If you accelerate progressively down hills (ie - no kickdown, let the engine ramp up RPMs slowly... but quickly enough) then keep backing off the throttle going back up them - of course, don't drop lower then the speed limit... but don't let the tranny kick down if at all possible (might be easier on something like a diesel car... tho the V70 has plenty of low end torque courtest of variable valve timing and a LPT) then you can save even more on fuel.

I tried cruise, no cruise but trying to save fuel, and driving normally for a week each on my way to work - and no cruise, but trying to drive to save worked the best - 5.7L per 100Kms (I was driving a diesel car), 6.0L per

100Kms with the cruise on, and 6.1L per 100Kms driving with my lead lined foot.

Air-con was running at all times.

Our 960 got 8.89L per 100kms cruising at around 115-125 kph with me and one person on a long highway run.... this is the best this car has got... gets low 9's if I drive without it on the highway... sometimes almost 11L per

Did not realise that the air con would increase fuel consumption

Ooh yeah, takes some power to drive aircons just like in your house. Cruise won't slow up for hills - saves a lot of fuel doing that.

It doesn't really use any extra fuel in my VW diesel (better A/C design and a smaller compressor then in the much older Volvo - as well as aerodynamics that favour windows-up driving).... But just letting you know the 'test conditions' didn't change for all three weekly runs... In the Volvo, the A/C makes the car drink a little more fuel... maybe 0.5L per 100kms more, and you can feel it sapping engine power...

I haven't tried windows down vs air-con on (because I hate windows down... loud and drafty interiors aren't my idea of a nice drive - its the reason i'd never be a convertible owner, that and the fact I live in Canada... convertibles here aren't practical).... studies show its better to run A/C... I know my car gets best fuel economy in the fall and spring - windows up, no A/C, minimal fan speed, no heated seats running. Any accessory will sap engine power and hurt fuel economy.

Volvo did a study and found it's safer to drive with the A/C on at 22C because you are at the highest level of comfort and alertness, they found if you go above 24-25C you get uncomfortable and reaction time is hampered, same goes with being really cold. May as well keep it on - air conditioning systems also will start to have their seals dry up if they don't run... so may as well run it.

aerodynamics

On my 740 Turbo having the AC on drops the fuel economy noticeably, usually around 2 mpg, but when the weather is hot it's worth it. You can also really feel it sapping power, particularly at highway speed it just looses all the "kick" it normally has. I haven't seen any difference at all in economy from having the windows down (back when the AC was broken) but the only time I ever had all the windows all the way down was around town, on the freeway it's too windy so I'd put them down about half way and open the sunroof to vent.

The best way to use A/C is to turn it on while cruising, and off while accelerating or climbing a hill or grade. You can get the fuel economy drop down to less than 1 mpg this way. I once built a switch that would allow the A/C to operate only when the brake light was on. Great for city driving.

Opening the windows creates enough drag to roughly equal the A/C drain on economy, at least at highway speeds.

You wouldn't wanna do that on a 240, the AC on those is marginal at best and just about worthless when the engine is idling. The 240 Turbos do disable the compressor under boost, not sure if the 700's do but it appears not to. That seems to make the most sense though overall, it's only under boost that the extra power is really needed.

The affect in fuel economy varies widely, the laws of physics demand that it'll decrease somewhat, but the design of the system and the rest of the drivetrain can make a big difference on how much. I'm all for good fuel economy but I'd rather spend a bit more on gas than have my butt glued to the seat with sweat.

That'd be fine if it wasn't too hot - it would not run long enough or effectively at idle, to do much cooling. And not too good when you first get in the hot car to go.

Never noticed any measurable difference in any car.

I'm not talking about running the A/C only at idle, folks! I meant I used it whenever I wasn't accelerating. The switch unit I built wasn't for this car, but would still work if the driving was more "stop 7 Go" than "stuck in traffic".

I also added a rocker switch to control the A/C power, so I could leave that $300 thermostatic switch alone, and just hit the rocker. That's a good idea no matter how you use the A/C...