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Old 10-21-2010, 11:28 AM   #1 (permalink)
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Default Car rattles when accelerating & poor gas mileage

Hi all,

I have a '98 Outback w/ 180k miles on it. For a few months now the car rattles when I am accelerating (sounds like it's coming from the engine).

On top of that, my gas mileage has been terrible recently. I have an hour commute to work (~45mi), which would use about an 1/8 tank of gas each way (1/4 tank per day). In the past week the car has been using a 1/4 tank one way at times!

Are these 2 issues related?? Any help either way would be greatly appreciated
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Old 10-21-2010, 11:45 AM   #2 (permalink)
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Originally Posted by kay2104 View Post
Hi all,

I have a '98 Outback w/ 180k miles on it. For a few months now the car rattles when I am accelerating (sounds like it's coming from the engine).

On top of that, my gas mileage has been terrible recently. I have an hour commute to work (~45mi), which would use about an 1/8 tank of gas each way (1/4 tank per day). In the past week the car has been using a 1/4 tank one way at times!

Are these 2 issues related?? Any help either way would be greatly appreciated
You have the timing belt done at 105 -110K? Any engine lights on - on the dash?

Also try running the actual milege numbers when you fill up next time miles vs gallons its pretty easy. Based on your details could be anything even the driver. Post more details on the car's maint history and actual milege
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Old 10-21-2010, 11:46 AM   #3 (permalink)
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Is it a metallic shaking sound? Might be a loose exhaust shield.

Go by miles per fill up, older Subaru gas gauges are notoriously off the mark at times. But to establish a baseline: how old are the spark plugs, plug wires, pcv, air filter, timing belt, etc?
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Old 10-22-2010, 01:46 PM   #4 (permalink)
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Could it be a bad knock sensor, not detecting detonation? That can sound like rattling, too.

Seafoam cleaning may help reduce the knocking, if it is knocking due to carbon build up.
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Old 10-23-2010, 06:58 PM   #5 (permalink)
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what is this seafoam?
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Old 10-23-2010, 07:10 PM   #6 (permalink)
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It's an engine cleaner in a spray can. You should be able to pick it up at any auto parts store.

Likely though, it's probably the exhaust heat shield like AWDFTW said. I think I have the same rattle. Does it only rattle when the engine is under load and at certain RPMs (mid range, like 2000-3000)? That's what mine does. I'm too lazy to get in there and tighten it and I don't foresee it causing any problems in the short term other than the noise.
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Old 10-24-2010, 01:06 AM   #7 (permalink)
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Kay, we can only help you if you give us more information. Are you still out there?
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