I noticed my average per tankful is down 1-1.5 MPG when its cold outside, like now in NY. (2010 5.0L Premium)
Anybody else noticed this?
Also, Since I got the car in June 2010, with just over 9000 miles, the total average is 17.8 MPG.
For the same type of driving , my last Infiniti G35X got total of 18.1 MPG

 

All cars use more fuel in winter. You are doing well.

The fuel economy of your V8 Jaguar ( 4.2 or 5.0 liters) compares very favourably with the 3.5 liter V6 in the G35X, that awd machinery uses quite a bit of fuel.

My 2001 Audi S4 (chipped) with the 2.7 liter biturbo engine uses more fuel than my 4.2 V 8 Jaguar XF.

Mind you, the Audi is blindingly quick.

 

With all due respect, Audi's, until recently were always one of the biggest gas pigs out there. Your winter mileage is good. Typically, the XJ will be slightly better as it is lighter.

 

Audis gas pigs? How dare you be so nice...My 01 A6 with the same engine as the 01 S4 drank gas like Charlie Sheen drinks booze. But in Charlie's defense, I have a very heavy foot and the car had some mods. Dueling banjos...nah spooling turbos.

 

Even the N/A Audis drink gas. My A6 gets anywhere from 5-8 mpg less than my S-Type. Both are V6 engines of roughly 3.0 liters. The Jaguar is also quite a bit quicker.

Mike

 

All wheel drive consumes quite a bit of fuel. The fwd Audis are quite fuel efficient. But this is a Jaguar site......Jaguars are generally pretty fuel efficient for their weight, especially at highway speeds.

 

You can save a bit of fuel by switching your climate control to manual mode and dis-engage the a/c compressor. I do this as I can warm up the car faster. It is also quieter than the auto mode.

 

Some random thoughts....

Very cold weather means longer warm-up time...which means more time spent running with the fuel injection in "cold enrichment" mode. This might account for at least some of your drop in fuel economy.

Also, some regions....not sure about yours....go to a "winter blend" fuel which can cause a drop in economy as well.

Lastly, some people will let their car warm-up for 20 minutes in the driveway while they're inside having their last cup of coffee. That'll knock your "average mpg" figures all to hell :-).

Cheers
DD

 

Modern cars should not be warmed up by idling them. The idle mixture is very lean and the engine will take ages to warm up.

Turning off the AC will have no effect on fuel economy. There is an anti frost switch which automatically prevents the compressor from running when ambient is just above freezing or colder. This is true of all automotive AC systems to prevent icing of the evaporator core.

"Winter" gas uses a higher proportion of volatile fuel, usually a big dose of ethanol, which has less energy per liter and accounts for a good deal of th fuel economy issue.

Mostly though it is just the cold car develops more friction for longer before it fully warms up. In some very cold conditions the car never fully warms up.

 

I have noticed a small decrease in fuel mileage this winter, too. 4.2, using 93 octane. As others have said richer running and less efficient in cold weather I imagine.

 

And nobody talked about 1 of the biggest reasons....cold air meens denser air, denser air meens more fuel to hit target air to fuel ratios. And class it also meens what, say it with me......MORE POWER

 

Just a reminder that it is recommended the A/C be left on at all times or turned on at least once a week for the seals to live longer.

So, even if the car is always parked outdoors in cold weather, if you get a chance to park in a parking garage, it might be a good time to cycle the A/C for a bit whenever you get a chance.

 

Leave it on Auto and any necessary running would be taken care of. AC systems cannot operate in near freezing temperatures and below. They would ice up if they operated.

 

Well, I started this thread because I never experienced this noticable increase in fuel consumption on my previous cars, driving the same area, using same gas stations. Must be the 'direct injection' or other thing particular to the engine management system.
As far as making more power in cold weather due to higher air density - this also means I must be using lighter foot on the accelerator for the same average speeds around here. So should even things out?

 

not true, the ac compressor is on to take humidity out of the air. Otherwise your inside windows fog up bad. The evep temp sensor will run hot engine coolant to prevent evap from freezing. Thisa is true wether its ice cold or blazing hot outside. This is why when that temp sensor goes bad by thinking the core is too cold you get blistering heat even if its a 100*outside

 

Not on the European AC systems I am familiar with. The anti icing sensor is right on the evaporator core. The shop manuals confirm that the AC will not operate below around 3C.(38F).

To take moisture out of freezing air requires that you cool it further. If the outside air is close to freezing you will produce ice, not water.

And how would the water drain out of the evaporator housing? It would form ice in the housing.

What you describe isn't feasible for auto AC. It's just physics.

 

is an evap case outside the car's interior or inside? Its inside the car. and last time I checked most people dont like driving around in freezing cars. I know every time I turn off the ac in the winter to get it hotter inside the car the windows fog up and I must turn it back on. Its drawing humidity out of the hot interior air. And I dont exactly see ac water dripping out under cars in the winter either. So the system must remove enough humidity to keep the interior windows clear, but not enough to produce water drainage. So yes the point is that the evap temp sensor(aka anti icing sensor) does indeed allow for ac compressor operation as long as the evap temp sensor doesnt show freezing temps. Then it cycles it on and off and brings more hot coolant into the ac plenum from the heater core till the core temps rise. And the ac system is capable of freezing the evap core even in the summer depending on system pressures and operation. Its not there to shut the system off in the winter months when freezing as youre suggesting. And we're not even talking about the new jaguar scroll compressors that are controled by the engines control module, which also control the alternator voltage output and knows the in/out currect flows of the battery. So now on new Jaguars (Like your 09 XF) When you replace the battery, the ecu battery counter needs to be reset for proper operation using IDS/SDD. And this is another reason you never hook the negative cable of jumpers to the battery terminal, but to the approved ground stud in the trunk. Otherwise the ecu will not see the voltage going into the battery because you circumvented the battery monitor bolted to the negative post.
You know maybe since Im in Texas and youre in Canada it would be fair to say that we each see differant system operations based on radically differant climates.

 

Evap case is outside the car on my Audi, Alfa Romeo, my SAAB and, as far as I know, my XF. The evaporator has to be colder than the ambient air to do anything useful. If it gets colder than freezing the ice will form on the matrix and clog the airflow.

The recirc flap allows cabin air to pass through the AC evaporator. Try running the ventilation system in winter with the recirc flap engaged and the AC supposedly ON and see how the windows fog up right away. That's why. The AC cannot dehydrate air at close to freezing temperatures. The AC will not run if the ambient air is colder than about 3 C even if recirc is selected.

I do not understand your description of the AC systems you are familiar with. It gets hot up here in Canada in summertime so the AC works the same up here as it does anywhere. European cars use an air blend method of heating the cabin. All intake air passes first through the evaporator to be cooled (and incidentally dried) if required and then through the heater box where part passes through the heater core if heat is needed and the rest bypasses the heater core and is then remixed downstream of the heater core to reach the desired temperature. The evaporator box is nowhere near the heater core.

 

[QUOTE=jagular;318353]Evap case is outside the car on my Audi, Alfa Romeo, my SAAB and, as far as I know, my XF. The evaporator has to be colder than the ambient air to do anything useful. If it gets colder than freezing the ice will form on the matrix and clog the airflow.[QUOTE]

NO its in the dash, youre thinking about the condensor in front of the radiator, and the evap temp sensor is either in(as in, in the fins) or in close proximity( like right on it) to the evap core

[QUOTE]The recirc flap allows cabin air to pass through the AC evaporator. Try running the ventilation system in winter with the recirc flap engaged and the AC supposedly ON and see how the windows fog up right away. That's why. The AC cannot dehydrate air at close to freezing temperatures. The AC will not run if the ambient air is colder than about 3 C even if recirc is selected.[QUOTE]
I do this all the time and until I turn off the compressor(AC switch) it does not fog up regardless of the recirc flap open or closed

The ricirc door when open "recirc" the air from inside the car, or recirculates it. With the door closed it draws in fresh air and regardless takes the same path in the unit. the intake is before the blower motor either recirc on or off. Its doesnt change the path in the box, that depends on the hvac settings, and either in manual or auto mode. Yes if the evap sensor sees feezing temps in the evap core it does shut off the ac compressor. Now if it 80* in the inside the car, even if its 20* outside. and you have it in auto, the ac compressor will be on. as long as the evap core doesnt go down to freezing, and if the cabin is 80 and lets say you have the recirc door open your gonna have a operating compressor. Ide print this all off of topix and the work shop manual so you could see it, but Im at home getting ready to go to bed.

Maybe pictures would help

 

and heres the info from jaguar for your car out of topix.
AIR CONDITIONING OVERVIEW
The air conditioning (A/C) compressor is a variable displacement
unit shared with XK and XJ. The displacement
(flow of refrigerant) is controlled to match the thermal load
of the evaporator.
The A/C system is controlled by the ATC module.

meaning the compressor doesnt actually shut off it just VARIES its flow by changing the displacement of the freon flow. On you car the climate control does alot more and fasterthan you even are aware of what its doing, and its now more efficient to have the ac cranked up while driving than to have the windows down, and definitly more comfortable than windows up and ac off. I dont understand why your trying to argue (or whatever it is youre trying to do)
On the statement I made about me in Texas and you in Canada, I am reffering to that maybe you and I are experiancing a differant type of operation because yes you see temp in the winter that are probobly below freezing and I do not. So under those differant condition maybe we are both correct(or wrong) And this was just a statement to let it ride and be done but you obviously didnt want to let it go. I would say sign up for topix and you can have a wealth of info on operation and your car. But it is really lacking and I have training manuals that go into much more detail and description of operation. But even those DO NOT cover module programming and system operation and controls under ALL types of operating conditions and many times we as techs are looking at issues that a customer feels is incorrect only to find that NO, this IS proper system operation under THOSE conditions.
So the short of it is I dont care to debate this any further and waste time or loss of income to research and cut n paste you into oblivion on Jaguars system operation. Youre misinformed. all this in response to your statement post #13 that ac doesnt operate in freezing or near freezing temps, yes it does just as long as the evaporator isnt freezing inside the car.......I'M DONE