Instant economy! - Morris Ox
Some of you might remember me posting a thread a few weeks ago about the Passat 1.8S 20V I'd bought off my former employer.

I was thinking of swapping it for something else because of it's poor economy, which had seen it struggle to get more than around 280 miles out of a tankful.

Well, guess what. The mileometer is currently on 341 and the fuel warning light has yet to come on. Just how was this fantastic improvement achieved?

I turned the air con off.
Instant economy! - Marcos{P}
I would say that if that's the case then you have a serious problem with the workings of the air-con system. The most power sapping part is the compressor so it could be permanantly on due to a faulty sensor somewhere within the system calling for cooling etc.
Take it to a good air-con workshop and they should be able to sort it out.

Best of luck

Just to let you know if I have my climate control on or off it makles no difference at all to mpg figures.
Instant economy! - Morris Ox
The only problem with the aircon was the person who used to leave it on all the time because the company was paying for all his petrol (i.e., me!).

Now I'm paying for my own juice I'd rather wind the window down instead.

Just goes to show how much juice aircon swallows.
Instant economy! - PhilW
Mr Ox,
That's still a hell of a difference and suggests something is wrong. As far as I can tell, having the aircon on on my wife's Xantia makes no difference to mpg. May still be worth following advice above and getting it checked
Instant economy! - PhilW
On a rough calculation - you are saying it makes a 20-25% difference to fuel economy - never heard of that before.
Instant economy! - Ian (Cape Town)
Now I'm paying for my own juice I'd rather wind the
window down instead.

... and increase your drag to the point where it uses MORE fuel than the air-con?
However, I'd agree with the other postings, it definitely sounds like the aircon is putting some severe drain on the engine!
Is there a noticable slump when you switch it on? {feels like like two fat people suddenly appearing by magic in the back seat?}
Instant economy! - Morris Ox
Ian, it doesn't appear to prompt anything other than a mild blip in performance and there's no sign that the system (the Climatronic, BTW) does anything other than perform properly.

Before I bought the car I simply used to leave it on all the time, my journey to work was about 10 miles, and together they probably had the same effect as towing a lead weight.

Now, I switch it off most of the time, and do my best to drive economically (changing up early, judging my approach to junctions/lights so there's minimal delay, not letting the engine labour etc).

Taken together, the fact is that the regular mileage while I was in my old job was around 280, right now it's reading 341 and probably has another 10-20 miles left in it.

I'm no techie where aircon'c concerned, but there genuinly doesn't seem to be anything wrong with it and I certainly took the trouble to get it checked twice a year.
Instant economy! - Marcos{P}
Could it be that the air-con in your car is just a badly designed system?
Some of the systems we use are much more efficient than others and you certainly pay for what you get.
Instant economy! - Cardew
I have VW climatronic(on a Golf GTI 1.8T 20v) and I carefully checked to see the difference between always on or switched off. I could not detect any difference.

I now leave it on all year, set at 20c.

Even with the compressor on your car faulty, and always engaged, I cannot see how it could make that difference to your fuel consumption
Instant economy! - PhilW
Have you tried driving in your new style with the aircon on? Or have you changed driving style and switched AC off at the same time and are attributing improved mpg to the AC being off rather than your new style when in fact it may have nothing to do with the AC??
Instant economy! - Morris Ox
Not tried that test yet, Phil, but let me give you the facts and figures on that last tankful now that it's sucked dry.

Filled up this morning with the total on 354 miles, and managed to squeeze 50.23 litres/11.05 gallons into the tank.

That equates to 32.04 mpg. Still nothing to write home about, but definitely about 4 mpg up on the average I used to chalk up while in my previous job and with the aircon permanently on.

I didn't think I was much of a lead foot before, so I can't quite fathom why a gentler driving style alone would account for that much of a difference. But may be tne real fuel misers out there know different.

Equally, I can't believe that having the aircon on all the time makes no difference. Must do if it's got to drive a compressor.

I'm under no illusions; the Passat 1.8S 20V is never going to be an economy car. But even in my motorway days the low 30s were the best it managed. I'd really like to see 34-35 out of it.
Instant economy! - Flat in Fifth

IMHO driving style has far far more influence on fuel cons than aircon.

OK maybe a significant difference if its a raging hot day, and/or your aircon is a bit iffy so the compressor has to work flat out virtually all the time thus consuming its 9hp or so. But with modern variable output compressors?

Better go now before DVD gives me a rollicking for surfing on a Bank holiday pm. (Just taking a T-Break from gardening!)

Instant economy! - smokie

On the Omega the multi display shows, amongst other things, instant consumption. On reasonably hard accelaration from a standing start this can drop to around 7 mpg. I was watching it yesterday, and on an overall trip (250 miles) I got 29.2 which I was pretty pleased with (it's a V6, 3.0). However, even on motorways, consumption when accelerating dropped to about 16 mpg, while when cruising it was at about 34.

So driving style makes the big difference. Better anticipation resulting in saving deceleration (?) and acceleration not only saves on fuel, but brakes and other wear and tear.

Aircon makes about 2mpg difference on my car, I reckon
Instant economy! - jud
Why do people constantly claim that using the aircon makes no difference to economy? clearly if the engine is driving a compressor then it is using energy which in turn is supplied via petrol/diesel.
Morris, your new driving style is responsible in the main for your new found economy, as smokie says a couple of mpg is saved (varies)with the aircon off.
Instant economy! - henry k
Spot on jud.
The loss of BHP may not be so obvious these days with even small cars having so much more power. I recall 20 years ago driving a low power car with aircon. When overtaking it was standard to just prod the aircon switch and the car responded as if it had changed down a gear and the power available was really noticeable. I think the same would apply with say an Escort sized car with bottom rated 1 litre engine.
I also seem to recall in those days small engined cars in addition had a down rated aircon because of the power required to run it sapped too much power going to the wheels.

Value my car