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2004 XT AT
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1,101 Posts
Discussion Starter · #1 ·
It's another "my fuel consumption has increased" question. I stated a new thread because I've got a couple of other symptoms and I'm wondering if there could be a common cause for it all.

1) During city driving, my average consumption has dropped from ~22 to ~17, compared with say a year ago (yes, I am sad enough to keep a spreadsheet ;-) The drop appears to coincide with having the car serviced in November.

2) But on a long run, the fuel consumption is pretty well unchanged from a year ago. Up to 32mpg (bear in mind 2.0 engine and UK gallons).

3) This winter I noticed a lot of steam when the engine is cold. I mean a lot MORE steam that I would expect, for a given ambient temperature, and more than I remember from the car in previous winters. It quite billows out the back, and I have to operate the rear screen wiper a couple of times to clear the condensation it puts on the glass. Once the car is hot, the steam stops.

4) No coolant loss. I haven't topped up since the car was serviced in November and the level is the same.

5) There is an unburnt fuel smell at the exhaust when cold, but there always has been (perhaps it's worse, though). The exhaust tip is sooty, but it always been. There's no fuel smell in the engine compartment or elsewhere so I am not suspecting a leak.

Any thoughts on what could cause that combination? I'm tending to think some sensor that affects fuelling when cold has gone south and is making the car run rich when cold, but normal when hot. But.. does running rich create extra steam?

Thanks

-- Steve
 

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Administrator
2007 Forester Sports XT 4EAT
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41,230 Posts
If you haven't replaced your front O2 sensor, that might be a good place to start. If the engine was running overly rich, I'd expect to see a P0420 CEL code, but perhaps it's not bad enough yet. :confused:

There are other possibilities:
  • Poor quality fuel.
  • Air filter needs changing.
  • Needs new spark plugs.
All guesses of course. :wink:

Bobby...

My MODding Journal
 

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99 UK S-turbo
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8,566 Posts
Air filter doesn't effect FE on an EFI, that's an old carb issue.

Lots of condensation is normal, I've always had to use the rear wiper to clear it in cold weather!

Running rich/02 sensor is a possibility, as is the fact its been especially cold, so more cold running, colder thicker oil, lots of heating (slowing engine warm up)/heated rear window/bum warmers (if fitted) etc all affect FE.

Simon
 

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2004 XT AT
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1,101 Posts
Discussion Starter · #4 ·
Thanks for the suggestions. Bobby, O2 sensor does seems like a good bet. Simon, I think you may be right regarding "lots of condensation is normal" as I noticed another Subaru making equivalent amounts yesterday. Maybe my memory is faulty about previous winters. I also remembered that at the service they put a heavier weight of engine oil in that I had before, still within spec, but great, just what you want in winter :-(

-- Steve
 

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99 UK S-turbo
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8,566 Posts
I'm running 0W30 edge and got an economy improvement of about 3-4%.....

Simon
 

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1999 Forester S Turbo 5MT
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1,960 Posts
Cold weather and heavier fuel consumption

Your point about the weather affecting fuel consumption may be of help to a lot of people Simon even though once pointed out it seems common sense. I see posts here and the US written by drivers who normally get their annual service done before the winter starts, but this year their fuel consumption seems inexplicably up (mechanical issues aside), but this is more than likely because of the extra cold, and in motoring terms those very low temperatures equate to heavier consumption for many reasons. The winter of 2009/2010 has been one of the harshest for a long time but more importantly, harsh in regions that don't normally get "real" cold. Areas like Northern US, Canada, Scandinavia and Northern Europe get something similar to this every year so it's par for the course, but for those of us further down the horizontal, the additional use of heated windows, higher blower speeds, more lighting than normal plus extra bum warmer time (nice one Simon) and longer engine warm up causes a marked increase in petrol useage. I imagine this would be a nuisance to peds and cyclists fume wise, in town traffic but even on the highway the thermostat is going to stay closed longer. I see on that program "Ice Road Truckers" that nearly all the lorries have radiator covers to combat this because coolant temp in diesels ends up being lower anyway and the driver would have no heating. I think I read a post somewhere about a 2009 diesel Foz that the owner couldn't get enough heat from in the cold and was looking to fit an auxiliary electric heater. His Subaru dealer told him this is a diesel "thing". I drove a Ford Transit and an Isuzu Trooper, both diesels, many years ago and found a similar lack of warmth inside in the middle of the winter. Something I came across recently though did interest me - I was advised by someone I respect that Te.co petrol is sh.te (over here anyway) and can mess with the fuel system on certain brands, BMW being one of them. I changed from the aforementioned (I feel about Te.co the way a lot of Americans feel about Walmart) to the smaller petrol retailers and my average has gone from 24 to 28mpg. The 24 was noted after I bought the car last September and after the initial madness of owning a turbo Forester, but the 28 has been measured since December when I changed petrol brand and includes the addition of a TD04 and an MBC a few weeks ago. So while Te.co is a few cents cheaper to buy, per tank it actually works out more expensive, oh and the possibility of mechanical issues. Also, as Sahunt was saying, based on the tailpipe output from his Foz and others too during this really cold spell,, one might be forgiven for thinking that Foresters are actually steam powered.
 
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