Air Conditioning. How much extra fuel is used?

[ringway]

The recent warmer weather should yield a decent MPG but this is tempered by the use of air conditioning.

As a percentage, how much extra fuel is consumed when the air conditioning is used?


TIA.


Ringway.

 

[Bosco]

Here's a link to the episode where Mythbusters tested out the aircon/fuel question.

Click Link

 

[camerafodder]

My experience is that bog standard aircon does increase your fuel consumption noticeably but if you have climate control it manages the aircon accordingly. In my old S211 I could hardly tell the difference as the fuel consumption increase was neglible when using climate control.

 

[sspeed]

I dont notice ANY difference when my Climate control is on or off.. It is left on 95% of the time and I still get 53mpg on a run..

 

[jpwilliams]

I dont notice ANY difference when my Climate control is on or off.. It is left on 95% of the time and I still get 53mpg on a run..

My experience exactly.

My view is that we leave the household fridge on all of the time, so why turn off the aircon?
Happy Motoring
Regards
John

 

[DSM10000]

The recent warmer weather should yield a decent MPG but this is tempered by the use of air conditioning.

As a percentage, how much extra fuel is consumed when the air conditioning is used?


TIA.


Ringway.

Why would the warm weather give bettter fuel consumption? Emgines work most efficiently when supplied with cooler and denser air surely?

 

[whitenemesis]

Engine warms up more quickly

 

[corned]

Why would the warm weather give bettter fuel consumption? Emgines work most efficiently when supplied with cooler and denser air surely?

The comment is aimed more at diesels, and more so with the bigger diesels. They are nototiously slow to warm up - more thermally efficient, you see. I see almost 10mpg difference in short to average length journeys between the height of winter and the height oif summer.

As others have said, there is no noticeable difference between running with, and without, aircon for a lot of models. Mine included.

 

[DSM10000]

Engine warms up more quickly

Yes but the cooler the air is the more oxygen is available per unit volume and that gives beeter fuel burn. Hence intercoolers being used on forced induction engines.

 

[DITTRICH]

It depends.
The aircon compressor does require power to operate and fuel is required to produce the power. The difference will be much more noticeable in town at low speeds than on the motorway. The internet says anything between 5% and 10% increase in fuel consumption. Modern climate control systems have the ability to switch off the compressor which will decrease fuel consumption.
It's difficult to test because SWMBO always insists on having the windows open in Russia even when its bl**dy hot. But on long trips in the c230k saloon (400 miles to Latvia from Moscow) I used to get 34mpg WITH the aircon on FULL on very hot days. In germany, similar thing, 27mpg but the roads are better and alot faster.

 

[DITTRICH]

Yes but the cooler the air is the more oxygen is available per unit volume and that gives beeter fuel burn. Hence intercoolers being used on forced induction engines.

My c230k performs noticeable better when the outside temperature is very low. The hotter it is and the higher it is (the Alps) performance falls off. I always thought along the lines you mention and this is sort of confirmed by my experience.

 

[corned]

Yes but the cooler the air is the more oxygen is available per unit volume and that gives beeter fuel burn. Hence intercoolers being used on forced induction engines.

Yes, agreed. But not when it's still cold. And it's still cold for a long time, comparatively speaking.

 

[moonloops]

My c230k performs noticeable better when the outside temperature is very low. The hotter it is and the higher it is (the Alps) performance falls off. I always thought along the lines you mention and this is sort of confirmed by my experience.

Supercharged engines just like turbo charged ones are affected by air density and heat.

 

[davidsw]

The Mythbusters video was interesting but why ever did they not use the same vehicle for the test . That would have been more proof than using two seperate vehicles.

 

[johnsco]

On two E300TDs with aircon and our E430 with climate control, I've never been able to detect any discernable difference on consumption.
Other variables have much greater effects.

On my old (1995) Jeep Cherokee 2.5TD ... The Italian VM diesel engine with an Italian aircon pump ... the effect was quite noticeable.
You could hear the engine note change very clearly as the aircon pump clutch engaged and disengaged.
It wasn't very fuel-efficient anyway, but it appeared to drop between 5% and 10%.
Not very scientific - But the effect was quite noticeable.

 

[gIzzE]

I think it depends on the car, a 1.8 litre will certainly feel it more than a 3 litre.

I know when we had an Aygo you could feel the power drop off when the air con was turned on.

I notice no difference at all with my E350cdi, the differences are there I'm sure, but so small slight changes in driving style, location, time of day wipe out anything noticeable difference between having climate on or off.

Plus, when you turn it off you get mould growing in your system and getting the climate system cleaned out to stop funny smells will wipe out any small fuel saving imho.
Plus, I pay so much for my car in depreciation, insurance, tax, fuel etc. that trying to save £2 a week by turning off the climate just isn't worth it for me.

 

[gIzzE]

Yes but the cooler the air is the more oxygen is available per unit volume and that gives beeter fuel burn. Hence intercoolers being used on forced induction engines.

BMW say that the typical diesel engine uses around 40% more fuel before it gets to temperature.
At 25°c that takes around 5km or 5mins.
At 5°c that takes around 20km or 15mins.

Most peoples journeys are sub 20km/15mins.

So, if you are only driving 12 miles to work in the winter your engine is not even getting to temperature and thus will use loads more fuel.

Cooler air is good, the M3 CSL felt noticeably sharper with a cool ambient temperature, but I can certainly see a massive difference between my e350cdi at single digit temps. compared to when it is +20°c outside.

 

[corned]

Agree with all of that.

Plus, I pay so much for my car in depreciation, insurance, tax, fuel etc. that trying to save £2 a week by turning off the climate just isn't worth it for me.

If the additional cost of runing the system came to as much as £2 in the whole ownership of the car, never mind per week, I would be surprised!

 

[bedwards1966]

I can't say as I have climate control so don't always know when it's on, and even then you can't tell unless you use a tankful of fuel both on and off under the same conditions.

However, I don't think it's great. I was told by an aircon person that your looking at about 3-4 hp to run it, so figure it out from there. A 60 hp car is going to notice it slightly, your 4 litre engine at 280 hp really won't care, and the consumption difference is not going to be measurable.

The advice seems to be that at low speeds round town it's more fuel efficient to have the windows open, at higher speeds the aircon works out cheaper.
Personally for the immeasurable cost I think it should be left on whenever it's needed.

 

[renault12ts]

Here's a link to the episode where Mythbusters tested out the aircon/fuel question.

Click Link

Thanks for the link.

But their experiment was incredibly flawed. They used two different vehicles and somehow concluded that A/C used more petrol. Better if they had run back to back with the same vehicle. Fail.