What kind of effect does air con have on fual consumption in the X300? Enough to make it worth thinking about? Has anyone done some MPG experiments?

 

I've never experimented becuase, regardless of the result, I have no intention of going without the A/C :-). However, now you've gotten my curioisty going so I just might give it a try.

I doubt that the difference will be much as modern compressors are not as parasitic as those from the 20+ years ago.

Cheers
DD

 

I live in Vegas, so the AC is a must. I have noticed little to no difference in fuel usage since summer ended.

 

I'm with Doug on this one.

Ours is a "big block" 3.2ltr, which the US never got. On a recent interstate run in it, quite cool weather, so a/c OFF, and returned 9.1L/100K, same run last week with the a/c ON, and returned 9.4L/100K, and for a 3.2 engine the difference is "bugga all" so the 4ltr should be even less of a variance I think??.

Our V12 XJ-S returns 11.2L/100kms no matter what is on or off, on the same interstate run. NOWHERE near that around the suburbs hahaha. It has the Sanden a/c compressor upgrade.

 

Thanks for the figures.

Mine is 3.2L Brit import.

 

Ok, So I know its not a Jag but I believe it will still be relevant.
See below the Top Gear test, where they rove a 4.0 Audi A8 from London to Edinburgh AND BACK (800 miles ) on one tank of fuel.
According to JC the A/C can account for around 6mpg!!!

I've included a couple of vids showing the test.....a MUST see for any reason

http://www.youtube.com/watch?v=GIHdpmTIrFw part 1

http://www.youtube.com/watch?v=_JO-GhYkwrM part 2


OR >>>>>>>>>>>

You may also find this intersting.
Top gear AGAIN....This time the task is to drive any production car on one tank of fuel from Basle in Switzerland to Blackpool in the UK
Obviously MPG is very important to discussions and practical tests on A/C, heated seats, windows down etc etc are all there

http://www.youtube.com/watch?v=HPwrSn_Exts part 1 of 3

http://www.youtube.com/watch?v=7h9iMO61NDk part 2 of 3

http://www.youtube.com/watch?v=FSx0b7wABTA part 3 of 3


Cheers

 

As my daily drive includes about 50 miles of steady speed highway travel I did a little informal testing today. I simply used the trip computer (which is fairly sensitive) with a fresh "reset" in each direction, 25 miles with climate control off and a 25 mile return trip with it turned on, 70mph, using cruise control

I come up with a whopping .2 (2/10ths) mpg drop in fuel economy using the A/C.

Obviously this isn't very scientific but even if we fudge my results quite a bit I'd feel quite safe in asserting that the difference shouldn't be more than 1.0 mpg....and most likely much less.

Cheers
DD

 

Audi A8 has inefficient A/C compressor?

 

NO, JC is a BIG guy with a HUGE right foot, am I right??????.

Anyway 6mpg variance is what we used to get in the '70's with York piston type compressors, IF anyone is old enough to remember them.

Mainly fitted to V8 engines, as fitting one to a 6cyl would stall the engine at idle.

 

I remember them well. The GM/Harrison used on the older Jags isn't much better....when engaged the power loss can be very easily felt. On my older Jags there was a solid 2-3 mpg penalty.

Although a tiny motor might suffer more under the load of an a/c compressor the 6.0 mpg penalty on a modern car doesn't seem reasonable to me.

Cheers
DD

 

Jim-

I stopped watching the first video at the :30 sec mark when JC came out with the old myth that fuel is more dense first thing in the morning because it's cold. I remember seeing the episode on TV were they threw out all sorts of other unsubstantiated statements.

Fuel is kept in underground tanks where, much like wine caves, the temperature doesn't vary more than a few degrees from the hottest summer day to the coldest winter freeze. The variation from one day to the next, given the thermal mass of hundreds of thousands of litres in the tank, is zero.

My own observation is that the variation in consumption with AC on/off is too small to measure or conclusively attribute to one variation or another.

Cheers

Mike