(G) Panda 4x4 twin-air mpg

Thanks.

I travelled down the M4 to London, and back, today, so I checked the mpg at 70mph with/without AC on.
(I didn't bother measuring with the ECO button on - that's just a button for when my wife or daughter is driving).

Driving for about 20 minutes at close to 70 mph, with the aircon on, fan speed 2 and windows closed, gave about 49 mpg.
Driving for about 30 minutes at close to 70 mph, with the aircon off, fan speed 2 and windows closed, gave about 55 mpg.
These mpg figures varied with uphill and downhill stretches, so they are not exactly comparable, but they indicate about a 10% effect on mpg at 70 mph, due to the aircon.

I have to say that I was surprised that the difference was so high. I have not seen any significant effect with the AC on the Multipla (although this is a 1.9 JTD).

The test was with a TA Lounge, not a 4x4, with 1600 miles on the clock.

They're also based upon the inaccurate trip readout also I take it and not a brim to brim test

I think we can conclude that aircon on the TwinAir motor does use extra fuel.
Also, I think the more economical your driving style the more apparent it is.

Did anyone see top gear last Sunday. The one with wolverine?
They said the Vauxhaul Astra star track car was considerably slower with the aircon switched on.

My Twin Air overall is 33mpg over 3800 miles, my 3ltr Diesel Audi Q5 does better than that, different driving etc but rather annoying all the same.

Running the aircon on any car will reduce economy. A/C takes power from the engine, and that power has to be paid for in fuel.

How much, and whether or not you are able to notice the difference, depends on many factors but is basically down to how much cooling is required, and how long it's switched on for.

Ecodrivers will certainly notice a bigger difference, partly because they are using less fuel to cover a given distance, and partly because it takes them a little longer to cover that distance, so it's a 'double-whammy' effect.

In the worst case scenario in my 1.2, running the A/C reduces economy by over 10mpg.

That's true. But I was not going to stop and top up with petrol, at motorway prices, every 20 ~ 30 minutes ! (and this would still have been subject to error due to different 'brim' levels when only filling up with 2~3 litres, different fuel types, different driving speeds around service stations, etc.)

The trip computer measurements may not be highly accurate, but should be fairly consistent between the two tests. For certain, the error in the trip computer measurement between the two tests is much smaller than the indicated 10% effect due to the aircon being on or off.

I'm not trying to specify the exact effect of the aircon, but I am saying that the effect of using the aircon, on my car, at 70 mph on a fairly level road is to increase fuel consumption by about 10% (say 5% ~ 15%, taking error into account).

Absoulutely. The trip computer isn't particularly accurate, but it is consistent between readings when used in this way.

Yes, at 70mph, that's exactly the effect I'd expect to see.

This seems logical, assuming that engine efficiency is a fixed parameter.

However, both my previous cars (Renault Clio dCi 80 and Alfa Mito 1.3JTDM-2)
appeared to use no extra fuel with air-conditioning on, despite my checking
many times, over thousands of miles.

My theory is that the extra load improves the efficiency of the turbodiesel
at low power levels (I usually drive deliberately for maximum economy)

Unfortunately, this doesn't seem to apply to the petrol Twinair, for which
I'm finding a fuel penalty of about 6% with the air-con. on

It's still a great engine though, and my Trekking's managing to do
better than 50MPG average wherever I go



Chris

I think that the extra torque of Diesels is better able to carry the load of A/C compressors than relatively low torque petrols, which need to rev higher, particularly at idle, to prevent stalling.

I've driven small engine petrols - admittedly a long time ago - which were noticeably slower and more laboured, and thirsty, when the A/C cut in.

Having said that, the TA does not feel to be struggling with the compressor operating, but then this is probably masked by clever software and a less power hungry modern compressor.

I was a passenger last night in a VW Polo, the one with the small three cylinder engine, and I could barely notice the compressor cutting in, either by sound or by engine note, and the car became ice cold very quickly.

That sort of figure is pretty disappointing to say the least!

My old Daewoo Leganza was more economical with the aircon on than off !
This was because I only used the aircon when the weather was really hot, and I tended to slow down to enjoy the cool breeze !

If you've got air con and its hot then use it, otherwise why bother paying for it in the first place. I'd use my MJ aircon if it worked !

Don't forget to put the recirculation on as this will minimise the energy requirement. Don't forget that the car needs more energy to cool it down initially, and then less to maintain it at that temperature, so longer runs will be more economical.

Have just returned from weekend in Norwich and using ac most of the time achieved 41.10 mpg using brimful tank to brimful tank...mostly Motorway and dual carriageway...52 mph average according to trip.
Engine still feels tight so should see figures increase.
Regards

Just done a 140 round trip to the royal welsh show in my 4x4. Mainly single carriage a roads, lots if bends and hills and trip computer showed 52mpg. All miles done with ac on and still only done 660 miles in total.
I noticed that two things kill your mpg: speed and hills. 40mph stuck behind.a lorry was the most economical. Getting about 35mpg in my daily 2.5 mile commute to work. Downhill getting to work, uphill going home.

Sorry to resurrect a slightly old thread, but this makes interesting reading regarding mpg.