cost of fuel when idling with air con on

tomstickland

First I found of any use was:

I can tell you that my 4.3 uses about 1 gallon while idling 2 hours. That
> is idling with the heater on, 4 ways working and powering 600 watts of
> light-bar. I leave it running when on calls to keep the lights on and so I
> don't have to head back to the station in a cold rig.

Let's halve it for a 2.0 engine.
Call it 1/4 gallon per hour.
£5 per gallon, talking about £1.25 per hour. So 40 minutes is 80p.
A car capable of 30 mpg would be able to cover 40/60*1/4*30 = 5 miles on that amount of fuel.

tomstickland

Found another link now

Every 10 minutes of idling costs you at least 2/10 (0.2) of a gallon of gas

So that's saying 1.2 gallons per hour. Quite a lot different from previous estimate.

Probably bad data, because for trucks

trucks consume about eight-tenths of a gallon of fuel per hour when they're idling.

tomstickland

This is interesting:

In our tests we found that a/c usage increased fuel consumption by 12-15 per cent.With the a/c on, the idling engine speed is increased to take the load off the compressor, which increases fuel consumption. With the a/c off, the fuel flow rate at idle on the Wagon R was 0.59 litres/hour, which jumped to 1.02 litres/hour the instant the a/c was switched on.

Now that's making sense. 1.02 l/hour is in good agreement with the 1/4 gallon per hour.

Call it 1 litre per hour.
Car capable of 30mpg is doing 6.6miles per litre.
40 minutes uses 2/3 of a litre, which is equivalent to just under 4.5 miles of fuel (30mpg).

scbk

There's a blurb in my manual about not leaving the engine idiling. Apparently 3mins idiling is the equivilent of driving 0.5 mile.



Idiling with air con on should use more fuel aswell because of the extra load

tomstickland

3 mins equiv to 0.5 mile seems about right. Then 40 minutes would be 40/3*0.5 miles, which is about 6.5miles.

mymatebob

photome wrote: »

I dont sit outside schools but what is the offence?

I knew I had read something about it.

It is an offence against the Road Traffic (Vehicle Emissions) (Fixed penalty) (Scotland) Regulations 2003.

photome

Thanks for all the replies

AdrianHi

photome wrote: »

I dont understand how it can be doing the engine any harm at tick over speed. Bus engines rarely get over tick over speed all day (they are governed) and some diesel generators will run all day at very low revs. Diesels as far as I am aware will go on for ever at any revs so long as they are at operating temperature
Could you tell me the damage it may cause.

I must add it is a company car and i dont pay for the fuel. It has done nearly 100000 and never had a problem so cant be doing to much damage

I got the impression you had a young modern diesel, perhaps not.
The latest EU4 2004 onwards diesels feature all manner of emissions controls features older simpler and more dependable diesel never had. Exhaust Gas Recirculation is one. Some of the exhaust gas is feed back into the engine to burn it some more and get the emissions down. There are cases around where these new diesels run around town a lot can have problems "gunging up" inside, sitting at idle with the engine not getting the correct airflow for extended periods is not particularly good for it. Ice cream vans and generators etc. are design to be standing still and have cooling systems to suite.
It is a case of increased risk, not definitely going to have a problem. May be you are cruising at 70mph on the motorway the rest of the time and this gives things a chance to clean out.

banger9365

is this thread you was loking for http://forums.moneysavingexpert.com/showthread.html?t=911337
and it's 10% extra feul usage with the windows open not with the aircon ,it less
http://www.coolcaraircon.co.uk/questions.htm

Pew_Pew_Pew_Lasers!

AC on or off, makes no difference in my car whatsoever.

I leave it on all the time. Never goes off. Better for the AC system, keeps the car interior dry, and stops me from smelling.