Author Topic: A/C and MPG... (Read 3434 times)

a930rocket · « **on:** July 24, 2011, 08:25:30 PM »

What does everyone get with and without the A/C running?

I was getting 26 without A/C and and with it running, I'm getting 18-20 MPG. Any thoughts? Bad compressor or tired engine (145K miles)?

DesktopDave · « **Reply #1 on:** July 25, 2011, 07:11:28 AM »

R12 or R134? The higher pressures of R134 on converted systems tend to suck up more power. However, my A/C doesn't work at all.

sqlpython · « **Reply #2 on:** July 25, 2011, 01:59:08 PM »

Last 2 weeks it has been in the mid 90s and low 100s in New England.
This summer New England has been much hotter then usual.
Anyhow, my 93 318i with std 5 spd will average about 27mpg w/o AC..
With AC on the car will be about 24mpg.
My vehicle just turned 108k..

dakon · « **Reply #3 on:** July 25, 2011, 11:47:04 PM »

a930rocket, i was just about to make this EXACT same post....

My odo is not working right now, and i have NO clue what fuel consumption i am getting, here in dallas its 100+ every day. so i use the AC every time i drive the car now... Hopefully more people will chime in soon!

a930rocket · « **Reply #4 on:** July 27, 2011, 05:51:39 PM »

Sorry for the delay Dave, but I'm running an R12 system (Freeze 12 as a refridgerant).

I'm just surprised at the difference MPG with the AC on and off.

I suspect with an old original compressor, it might be inefficient or placing a lot of drag on the engine. I can feel and hear it kicking on and off.

bmwman91 · « **Reply #5 on:** July 27, 2011, 07:32:30 PM »

I have been thinking about reinstalling AC on mine (well, pressure from my other half has made me consider it lol). Has anyone ever retrofitted the AC compressor from a much newer, more efficient car onto theirs?

DesktopDave · « **Reply #6 on:** July 27, 2011, 08:20:53 PM »

Yet another thing an M44 can donate...tensioner, lower timing case, serpentine setup, electrical aux fan, steering rack and now the compressor...the list goes on!

75BMW2002 · « **Reply #7 on:** July 28, 2011, 10:57:41 AM »

I am getting around 26 MPG running my AC in these 95+ temp days. That is about 3 MPG loss vs. the winter months. My car has 126K miles by the way. Also, 145K miles on a M42 engine shoudl not be a "tired" engine unless you have run it extremely hard and not maintainted it well but the old compressors suck a bunch of HP as compared with some of the more modern compressors

Bob

a930rocket · « **Reply #8 on:** July 28, 2011, 09:21:30 PM »

I'm not sure of the history on mine, as I've only had it a few months and driven it about 3000 miles.

Dave and others, is there a more efficient compressor that is a direct swap without the serpentine belt?