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Registered
2001 Forester Auto
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88 Posts
Discussion Starter #1
Hello,

1999 Forester L, 225,000 miles.

I have been searching the threads and a few with similar problems have come up, but not the same. A very low pitched knock started this winter. At first, I could only hear it when idling in calm conditions, no radio, no fan on.

In the last two months, the noise has increased to where I can always hear it while idling, plus, the knock is easily heard when it is first started, for about 1 -2 seconds, or about 5-6 knocks.

When idling, the low-pitched knock can be heard easily on the left side by the front wheel, but no so easily when listening in the engine compartment.

No codes and no other symptoms the engine is not operating properly. As far as I am aware, the knock sensor is original.

I am wondering whether I should just replace it, or pull it out and test it first.

Thanks for the advice.
 

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2009 Forester X 4 A/T
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305 Posts
My opinion-The knock sensor isn't your culprit. Under no load the timing will be at its base level and shouldn't need retarding to reduce pre-ignition knock, which sounds more like a rattle unless it is really bad under heavy load. Sounds more like a rod bearing going south if it is low pitched. Higher pitched knock is often piston slap- especially at start up (I have a Chevy V-8 truck with skirtless pistons which has piston slap).

I'm sure some real Subie experts will reply soon.
 

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2008 Sports 2.5x
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335 Posts
rod bearing gets second vote

Hello,

1999 Forester L, 225,000 miles.

I have been searching the threads and a few with similar problems have come up, but not the same. A very low pitched knock started this winter. At first, I could only hear it when idling in calm conditions, no radio, no fan on.

In the last two months, the noise has increased to where I can always hear it while idling, plus, the knock is easily heard when it is first started, for about 1 -2 seconds, or about 5-6 knocks.

When idling, the low-pitched knock can be heard easily on the left side by the front wheel, but no so easily when listening in the engine compartment.

No codes and no other symptoms the engine is not operating properly. As far as I am aware, the knock sensor is original.

I am wondering whether I should just replace it, or pull it out and test it first.

Thanks for the advice.
I'll bet you lunch that its a rod bearing. Cheaper to fix it before the engine throws a rod based on personal experience with another engine that started knocking. The engine will run until it fails. My wife called me one day from the grocery store, said the engine would not start but the knock was gone replaced with another expensive noise(s).

Cylinder was scored among other things.
 

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2001 Forester Auto
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88 Posts
Discussion Starter #4
Thanks fdx and loco

With that many miles, I am wondering whether it's worth it to fix, or run it until it goes? The head gaskets were replaced 2 years ago, along with a lot of the other stuff that goes along with head gasket replacement, to the tune of $1600.

I know this is a subjective question, but how long could I go until it should be replaced?

Thanks again.
 

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2015 Forester X 6MT 6-Gear Manual
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1,373 Posts
Run a thicker oil 5w-40 rotella or similar and a Filter that DOESNT have a high bypass rating like a large wix or purolator classic or Delco (champion labs). OTW time for a newer(er) car.
 

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2001 Forester Auto
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88 Posts
Discussion Starter #6
Knocking Follow up

I noticed a thread recently about making sure people post a follow up for problems for eventual solutions....

My mechanic that did the head gasket work 1.5 years ago spent about an hour looking and listening. He stated the knocking problem (what I call knocking) is likely due to the mileage combined with the short skirts on the pistons, and the fact the pistons are moving horizontally. Basically, the pistons, at idle, "wobble" slightly, thus creating the noise. It is still not very loud (I can hear it both inside and outside the vehicle while idling), and I cannot hear anything during normal driving. Otherwise, no problems or codes, so I will just continue to monitor. I did see recently an article someone posted regarding subaru noises, which backs up the mechanic's assertion. I forget who posted that, but thanks. I used 91-93 octane for a few months, and it did not appear to make a difference.

Later
 
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