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I read recently a report that showed driving with windows down makes very little difference in real life consumption - its a bit of a myth. Increase in fuel consumption with a/c varies wildly from model to model can be anything from +2% to 20%. Small economy models suffer more.
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On most cars at 50mph
Are you actually claiming to have gone over 50 mph in a car Rattle? I think you're just bragging to be honest. It's a well-known fact that at 45mph your teeth dissolve and your brain turns inside out. Stands to reason.
As any fule kno mimsing on A roads is the economical way to get about. No car can reach 20 mpg on a motorway even with no windows at all.
Stands to reason.
Dunnit?
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Driving with one's tyres underinflated probably affects fuel consumption more than the a/c; there are so many variables affecting the overall consumption. I'd rather keep my aircon serviceable by using it and I'd rather have the windows shut and cool air circulating than buffeting, from open widows, blowing my toupe off and deafening me.
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This link was posted here a couple of months back, which amongst other things tests the aircon / windows open theory.
www.thule.com/Thule/Page____90595.aspx
It reports that, at speed on the open road, aircon saps very very little power and makes almost no difference to economy. But it DOES have quite an impact in stop / start town driving.
Open windows make a lot less difference than is believed -- about 0.2mpg.
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For many people the cost of depreciation outstrips the total cost of fuel so the odd few pence saved or used with or without aircon or windows is not something to loose sleep over.
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Unless you bought a 4 litre V8 auto for £800 lol wonder how many times i've spent in fuel compared to vehicle price lol.
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I've been reminded in recent weeks of the importance of servicing in terms of fuel economy. Gave the Volvo it's 144k service a couple of weeks ago, DIY but to the book (plugs, oil and filter, air filter and fuel filter). The service was not massively overdue (actual mileage 144,500-and-something). Old oil was filthy, despite doing only the 12k duty Volvo recommend. Air filter was also black (again this was changed last according to recommendations)
Fuel consumption has improved from 31 to 34 mpg. Driving the same way, same roads. Can feel it needs less throttle at a motorway cruise than it did, and feels perkier on part throttle. I suspect this was something to do with the plugs, as it's also far keener to start in the mornings, but the clean air filter must also play a part.
All this on a service that was not actually overdue. Can you imagine the result in 10,000 miles or even 20k, if I'd not bothered to do it? Assuming the turbo would have tolerated that mileage on the same oil of course.
Maintenance is critical. I know a few people who never bother to have their cars serviced, who can often be heard complaining about fuel economy.
I suspect this (and tyre pressures) play a bigger part in real world economy than air-con use.
Edited by DP on 16/06/2009 at 10:33
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Fuel consumption has improved from 31 to 34 mpg.
I think it is more likely due to the warmer weather of spring/summer than anything else.
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i agree in winter our 850 2.5 10v does about 25mpg in summer it does about 30mpg, and the air-con is used a lot more in summer then winter.
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Air conditioning is a luxury, just like like auto trans, and luxuries have to be payed for.
Edited by rtj70 on 16/06/2009 at 16:40
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Air conditioning and fresh air are not equivalents, so it's a pointless comparison.
Submarines and air raid bunkers have air conditioning, but most people would prefer real fresh air.
Incidentally I've always dismissed plastic draught preventers as clip-on bling from the days of Ford Zodiacs with exterior sun visors, but having just bought another Volvo with genuine ones fitted, I am very impressed. With the window fully down at motorway speed there is just a gentle breeze, and the noise is deflected too.
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Submarines and air raid bunkers have air conditioning but most people would prefer real fresh air.
No they dont, they have air purification systems.
Not the same thing at al.
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>>Gave the Volvo it's 144k service ....
>>... it needs less throttle at a motorway cruise than it did, and feels perkieron part throttle.
If it's old-school ignition, the biggest improvement is caused by fitting a new set of points.
Timing and dwell angle both loose optimum settings as the heel wears and the contact surfaces burn.
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Well the last time I was driving on the M60 my speedo was on 70 so that would be about 67. Surely the MPG depends on the revs?
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Surely the MPG depends on the revs?
I always thought a car would inject enough fuel to keep going at any revs, overcome the load etc. On a hill to keep the same revs on the flat needs more fuel. Same for head-winds etc.
Edited by rtj70 on 16/06/2009 at 16:41
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But then we are talking about torque and that is is what the gearbox for but then modern ECUs know what gear you're in and know what load the engine is put under so I assume you're right that the fuel injection would inject more fuel if it was laboured even if the revs are the same.
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but then modern ECUs know what gear you're in
Not in a manual geared car though, probably only for a Auto?
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My little old diesel engine has a max torque figure of 360Nm. If I turn on/off/on/off the climate control the engine note seems not to change.
Maybe related to size of engine and the power/torque. With hindsight I wish I did as fellow grads and got a decent size car from day 1. Insurance more but cars not and you got a lot more for the overall money. (That was a reference to mid 90s)
Edited by rtj70 on 16/06/2009 at 16:54
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On my 1.2 16V engine even if I wind the windows turn (electric) you can see the rev counter rise by about 50 revs until the motor stops. I am not sure how much torque my engine produces but its not a lot.
On my old car (Fiesta 1.3 Endura) there was a large plug going into the gearbox above the reverse switch with about 6 wires going into it, I could only assume that was to do with the ECU.
On my dads car which has a hydraulic PAS system instead of my electric one again if you move the wheel even slightly you can see the revs rise.
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hydraulic PAS system instead of my electric oneagain if you move the wheel even slightly you can see the revs rise.
Yes my Astra G Had a electrical one, although the revs didnt rise, the lights used to dim ever so slightly, and would be Accompanied with a tone in the noisy power steering pump (AFAIK) i think the Astra one was electrically assisted.
The Vectra does not make any noise and the revs dont rise (not that i notice) the lights ever so slightly dim a little when the stewering wheel is turned
However to keep on topic, on the Astra and the Vectra when you put the A/C on you notice the revs raise slightly and it saps a bit of performance out of the accelration.
Edited by redviper on 16/06/2009 at 17:11
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Remember that all diesel engines and most recent petrol engines have closed loop idle control.
This means that the idle speed (especially on a diesel where the governor will be holding it to a set value) will hardly shift with a small change in load - as would be caused by switching on an electrical load or by the aircon compressor coming into operation.
Most diesel governors - especially the electronic ones - have a very steep idle speed/load curve, so you would not detect any change on a dashboard tachometer. Handy for driving slowly in traffic with "no feet" too.
659.
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I drove from Cheshire to London and back today with the AC on and my sunroof open as well. Does this make me a bad person ?
Better plant a tree or artificially inseminate a polar bear in penance I suppose......
;-)
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No Humph - It makes you COOL!
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Better plant a tree or artificially inseminate a polar bear in penance I suppose......
What d'you mean, 'artificially'? Call that a penance?
Do the thing properly if you want forgiveness HB.
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Blow the ballast - number one
lets feel the wind and rising sun
Upwards now from forty fathoms
Scrubber using extra gallons
bursting from the depths with ease
anxious noses sniff the breeze
Let`s go back down - said number two
lest fresh air turns us to glue
air-con running on forever
pulleys belts and compressor
Edited by oilrag on 16/06/2009 at 18:59
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This was covered on Mythbusters a few years ago.
en.wikipedia.org/wiki/MythBusters_(season_2)#AC_vs._Windows_Down
"Tests were performed under varying conditions (55 miles per hour (89 km/h) versus 45 miles per hour (72 km/h)). Also, the 55 mph test was using a computer to estimate fuel efficiency based on air intake, not actual fuel consumption, and showed A/C was more efficient. The 45 mph test consisted of running the tank until it was empty, and showed open windows were more efficient. This experiment - or one like it - is sometimes cited by the Magliozzi Brothers on Car Talk when presented with this question."
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I hired a suzuki swift on holiday in menorca. Auto with aircon.
4 up with luggage, turning off the aircon was the difference between going up a hill or not.
swift it wasnt.
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I remember reading a roadtest years ago - a Jag, I think it was........'Top speed 120mph, or 126mph with the air-con turned off'
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Which is the most sensible is also a good question.
With all the green flies around at the moment air con is best, with an open window the car soon fills up with the things, varies from area to area of course.
With a window down there is the increased risk of being bombed with bird poo, my driver side window took a big hit the other day whilst on the move, window was up and air con on.
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Hmmmm....My economy for the Silverstone trip this weekend is going to be much better then previously thought, not because I'm not using air-con bevause it's fairly cool this weekend but because my sister had a nasty accident in her FTO last week (some idiot in a Punto who didn't even brake before emerging straight into her front left wing/wheel), So shes borrowing the 4Litre Lexus (20-25mpg on V-power) that is the only car she feels comfortable driving owing to the total lack of effort put into steering accelerating/braking, And I'm taking the Cordoba Diesel estate (55mpg on normal diesel), thankfully it has climate control.
Edited by Webmaster on 18/06/2009 at 01:47
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On a lot of piston engined aircraft with aircon aircon OFF for takeoff is a checklist item as it does use power.
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My limited experience of flying light piston engined aircraft has never found me in one with aircon. However, there is a ability to pre-heat the engine intake air, to prevent icing; this is invariably put to "off", for take-off, so that engine power is not reduced.
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No I've not flown one with air con either.
Yes about the carb heat, you select it before take off both to check for ice and to remove any which may have accumulated while taxying. Gnereally select it before reduceing power for landing as there is more tendency for ice to form at low power settings. Nothing like a muggy summers day to cause carb ice to build up. You will avoid useing it for any extended period on the ground as it bypasses the air filter.
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In the handbook on my A6 it reads 'Under hard acceleration the aircon will briefly disengage'
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The last car I owned that suffered from carb icing was a old square shape Fiat Panda. Dont these little aircraft have fuel injection, ECUs, and other up to date technology that is found in cars? :-)
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Yes light piston engined aircraft mostly have injection, these days, but icing of the intake arrangements is still possible, if the conditions are right.
Edited by Armitage Shanks {p} on 18/06/2009 at 14:30
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Thanks AS, I would not like to think it was possible to push the choke in (too soon) half way through a take off! :-)
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