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08-24-2012, 11:51 AM | #1 |
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South East
Location: SOMD/ VA Beach/ Tampa, FL
Vehicle:2002 wrx WRB |
7 MPG drop while using AC
My commute is roughly 46 miles RT with 70% being highway. Per my scangauge 2, I've been averaging 19mpg per tank while driving very modestly. Yesterday, my AC belt snapped off at the very beginning of my commute home. So I just rolled the windows down and drove like normal. I replaced the belt last night.
Well today I checked the scangauge and was shocked to see I had gotten 25MPG yesterday (including the morning commute w/ AC on). I left the AC off today and returned 26.5MPG. On the highway, as soon as I turned on the AC the mileage dropped immediately back into the teens. I know AC causes parasitic loses, but doesn't 27% seem really high? Is this a sign my AC is not operating correctly? Additionally, what can I do to decrease the MPG drag of my AC? CLIFFS: Belt snapped yesterday so no AC, registered 7MPG higher (per Scangauge 2) than normal commute. Is my AC operating correctly?
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08-24-2012, 11:57 AM | #2 |
Scooby Specialist
Member#: 62408
Join Date: May 2004
Chapter/Region:
South East
Location: GWR, Florida
Vehicle:2002 wrx w/ STi guts 174k miles on Mobil 1 |
It would have to be a pretty dry rotted belt to snap, so your compressor may be really tight and about to seize.
However, I'm not convinced any scan tool can accurately measure MPG given the variable of fuel returned to the tank etc. |
08-24-2012, 12:35 PM | #3 |
Scooby Newbie
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not trying to sound defensive, but the scangauge is pretty accurate. by most estimation within 5% when i calculate miles driven/gallons to fill up tank
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08-24-2012, 12:36 PM | #4 |
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please tell me more about my compressor being tight. what does it mean, how do i measure, any preventative measurses?
this is the second belt in two and a half years and the last one was an oem belt |
08-24-2012, 12:58 PM | #5 |
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I agree about the compressor being tight. belts generally don't just snap. I'm honestly not sure how to test it. but they aren't too much at a salvage yard.
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08-24-2012, 06:39 PM | #6 |
Scooby Specialist
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Join Date: May 2004
Chapter/Region:
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Location: GWR, Florida
Vehicle:2002 wrx w/ STi guts 174k miles on Mobil 1 |
I'm surprised it's that accurate. I wonder what algorithm the Scangauge uses to "know" the fuel pump flow and the gazillion of other variables that don't even have sensors to monitor.
Anyway, back to the compressor issue. Was the belt just cleanly snapped, or was it burned / stretched at the break? If it was burned, the belt was just loose and the crank pulley spun in it until it let go. Was it squealing at all prior to breaking? Has the A/C recently been charged? An overcharge will cause compressor stall / lockup too, but I'm not sure how much harder it will be to turn before this happens. Nothing really explains the 27% difference though - but a silly question, since it's a bugeye.. have you had the fuel line recall / update done? |
08-25-2012, 11:28 AM | #7 |
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w/ the AC on and your given situation which i dont really know it could be putting you in OL fueling and dumping more fuel in w/ the AC on. like being on the very edge of the engine load scaling and then when the AC goes on the engine load goes up and moves over to the next cell. is your car tuned? stock map? that info would be helpful. also how tight was your belt? belts even after dry rotting last years.
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08-26-2012, 02:14 AM | #8 |
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in cant believe a 7mpg difference witout something being broke somewhere....ac clutch bearings going bad or idler pully bearings or the tune being on the edge of ol
is the fuel filter clogged??? |
08-26-2012, 01:39 PM | #9 |
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Fuel filter was changed a couple years ago, I'm still on stock tune. My only mods are downpipe and intake. Only code is p0136 (rear 02 sensor wiring)
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08-26-2012, 04:48 PM | #10 |
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Just cleaned air filter and maf.
Also going to change pcv valve. Do you guys think it could be the front o2 sensor (even if I'm not throwing a code?) I was getting an overboost code a while back... |
08-26-2012, 06:47 PM | #11 |
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change the fuel filter...reset the ecu
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08-26-2012, 08:31 PM | #12 |
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Ok... Will do tomorrow. Is there anyway to be able to tell if the fuel filter is bad?
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08-26-2012, 09:19 PM | #13 |
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I noticed a pretty sizable drop with a/c on as well, this was while cruising at 70/75 however. At 90 today, with a/c on it was in boost the whole time lol. Oh dear. You could pretty much see the gauge going down.
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08-27-2012, 01:42 AM | #14 |
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08-27-2012, 01:44 AM | #15 |
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yet another reason i like my 06....i can go 90 all day long at 100*F, ac on '2' and get 23-24mpg
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08-27-2012, 10:31 AM | #16 |
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Well yeah that's probably what I was getting. This drop is down from 30mpg.
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08-27-2012, 10:39 AM | #17 |
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i just made a lon trip (10 hours each way to the beach and back home) on the way there i got 29-30mpg with no ac. on the way home i was getting around 21-22 with ac on the whole way. gf was cryin cause it was hot out. so it does drop a good bit
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08-27-2012, 01:12 PM | #18 |
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08-27-2012, 08:52 PM | #19 |
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don't trust the scangauge...test it a bit more before you try and fix anthing. teh AC doesn't pull that much and shouldn't make that much of a difference
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08-28-2012, 09:23 AM | #20 |
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10-22-2012, 01:04 PM | #21 |
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10-22-2012, 02:41 PM | #22 | |
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Quote:
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10-22-2012, 10:01 PM | #23 |
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10-24-2012, 12:18 AM | #24 |
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weird
there is major drag somewhere?
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10-26-2012, 01:09 AM | #25 |
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My 05 does the same exact thing as yours. When my a/c is on the car is gets 2-3mpg less, give or take a few. Not sure...
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