Air conditioning and fule consumption

olias

OK, so It is widely known that having aircon on in your car can lower the fuel consumption. I'm not asking why...not very mechanically minded, lol.

What I would like to know, and can't seem to find, is...by what margin will it affect mpg, partivularly in a diesel ( I drive a Discovery TD5). Is it a negligable amount? or really significant?

The reason I am asking, is my wife is always leaving it on, I moan to her, and it causes an argument . Is it worth making an issue out of? If you are only talking about pennies over the coure of a tank of fuel, then I'll leave it. If however its going to knock a significant amount off the mpg and cost £££s, then I'll keep on about it!

Thanks.

Olias

Wywth

Turn off air con at lower speeds.
Efficiency improvement: Up to 8%
Air conditioning uses an incredible amount of fuel, so make sure it's turned off unless you really need it. The general consensus is it's more efficient to drive with the windows down and the air con off at lower speeds, but at higher speeds it's better to use the air con and keep windows up due to the extra drag caused by having windows down.
If you're not using your air con, it's worth turning it on once in a while as not using it can mean it stops working.
Also, don't keep the engine running. Drive off as soon as you start up and switch off the engine as soon as you reach your destination.

http://www.moneysavingexpert.com/travel/cheaper-fuel#drive

GolfBravo

olias wrote: »

by what margin will it affect mpg, partivularly in a diesel ( I drive a Discovery TD5). Is it a negligable amount? or really significant?

German ADAC Motorwelt (or was it AutoBild?) magazine did a multi-car test to compare fuel consumption a few years ago. If I remember correctly they found about 6% (on average) increased fuel consumption with aircon on. The smaller the engine (less torque), the higher the increase - I think there was a diesel E-class merc with only about 2-3% difference.

So how much is a full tank of motion lotion for your TD5 these days?

poppasmurf_bewdley

I have a 2 litre diesel Mondeo auto estate and the air-con is always on. I cannot detect any difference whether on or off. However, my old Astra W-Reg 1.6 did show a material difference with Air Con on.

olias

GolfBravo wrote: »

German ADAC Motorwelt (or was it AutoBild?) magazine did a multi-car test to compare fuel consumption a few years ago. If I remember correctly they found about 6% (on average) increased fuel consumption with aircon on. The smaller the engine (less torque), the higher the increase - I think there was a diesel E-class merc with only about 2-3% difference.

So how much is a full tank of motion lotion for your TD5 these days?

Just filled it up from the red light and it was £115 :eek:


Olias

mattyprice4004

It depends on the amount of power the engine has (more power = lesser percentage load for the AC) and also the AC pump in question.

My old Rover 600 turbo and my MG ZS both had a Sanden SDV16 pump, which are very efficient. Even though the ZS only had 99bhp to begin with, I hardly noticed a difference.

I then got an old Rover 400 with a different (Denso?) pump, and it destroyed my MPG

Arfa__

However much you do save by turning the AC off, do factor in the cost of repairing the AC in a year or so, due to lack of use. The AC ideally needs to be run fairly often, as the AC gas acts as a lubricant for the system. No ends of people try to use their AC in the spring, after being off all winter, to find it's dead. The better plan is to run is often, even in winter with heater on (don't worry it won't actually cool, or work against the heater).

colino

With a nice torquey engine like that the fuel consumption difference will be negligible and you have the benefits of a better driving environment to boot. Driving styles between the two of you will have a much more measureable effect than the drag the a/c compressor will have on the engine.
I worry about the poor souls who have recently bought euroboxes stuffed to the gunnels with equipment once, not so long ago, thought of as luxury car territory. Once their power steering, a/c, slushpumps and abs go faulty they will be heading to the scrappy.

forgotmyname

How longs a piece of string?

Fill up, Driver a fixed route with little traffic and aircon on. fill up at the same pump and repeat the router with the aircon off.

Refill and compare the results.

Every car will get different results.

Tiexen

Arfa__ wrote: »

However much you do save by turning the AC off, do factor in the cost of repairing the AC in a year or so, due to lack of use. The AC ideally needs to be run fairly often, as the AC gas acts as a lubricant for the system. No ends of people try to use their AC in the spring, after being off all winter, to find it's dead. The better plan is to run is often, even in winter with heater on (don't worry it won't actually cool, or work against the heater).

And it will help demist your screen faster as it takes out moisture.

Wongsky

Tiexen wrote: »

And it will help demist your screen faster as it takes out moisture.

Yes, true - but then you kind of have to keep using it, as moisture builds up on the evaporator.

Savvy users of air-con in cars will realise that ideally they'll give the evap time to dry out before journey end - else that tends to be the breeding ground for funky smells.

This is also why some climate control units, run the blowers, at a seemingly random period after the car has been turned off.