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Discussion Starter · #1 · (Edited)
I'm trying to figure out what the noise is! My car was recently the victim of some overheating damage which left it stalled out on the side of the road for a little while. I let my GF drive it for a small trip she had to make, and the reservoir tank cracked on her, leaking out all of the coolant.

She told me it was making a clanking noise afterwords, and we had the reservoir tank replaced at a firestone center in the town she was staying at.

The car made it back to me just fine, but now instead of just idling a bit rough (3 out of 4 O2 sensors went out on me), it idles rough at times, stalls out, and occasionally makes a horrid loud clunking noise toward the rear end of the block.

I performed a spark plug swap and changed the oil. After all of that, the clunk is still present, all be it a little less loud after the oil change which makes me think that maybe through the heat damage, an oil bearing on the crankshaft has slipped a little bit.

http://www.youtube.com/watch?v=jC6CtaX-cTc

Please help me figure out what this noise is, we've narrowed it down to a piston rod, but if anyone could speak from experience and let me know that it's just a sticking valve, I would love to have that peace of mind.

Matt
 

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Discussion Starter · #4 ·
Roflcopter

As much as I would like to blame her, I didn't check the fluids before the trip... at least that's HER copout... somehow that would've prevented the crack in the reservoir tank!

See dear... there's this thing called a THERMOSTAT!

**sigh**
 

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Sounds like possibly a dying cylinder. It's hard to say since it doesnt seem rpm dependant.

Need more info. Anything weird in the oil? Noise pick up speed when you give it gas? how long did she drive it after the tank busted?
 

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Discussion Starter · #6 ·
It's definitely RPM dependent. Forgot to mention that it doesn't happen at 1k RPM or higher. The throttle seems to take a few seconds longer to pick up too.

Nothing in the oil seemed too strange, no milky, gravy consistency to allude to water, etc.

She drove it until it overheated and shut itself off, almost getting her rear-ended on the highway.
 

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When I was diagnosing a possible oil separator problem on my '00 323 (slightly rough idle and several codes related to fuel trim, fuel control, and O2 sensors, all for both banks), I removed my oil filler cap to test for the amount of vacuum, and during this test I got the same intermittent loud knocking sound that you have. For me it only happened when the oil cap was removed and around idle or low rev as I recall.

You might have some sort of related vacuum leak. For me, the final culprit was a broken lower oil separator hose (see the story and pictures here: http://forum.e46fanatics.com/showthread.php?t=773551 ). The oil separator has 4 associated hoses which fail over time, and the oil separator itself can go bad as well. All my codes and rough idle were cured by replacing this one broken hose.

Is your check engine light on? Do you have any diagnostic codes? Other sources of vacuum leaks can be the rubber intake boots between the air filter box and the engine (they get cracks in the accordian folds, especially the "Y" near the idle control valve), or a leak around the gasket for the DISA valve. I never removed the oil filter cap after I replaced the broken hose, so I don't know if the knocking sound would occur again after the hose fix.

Hope this steers you in the right direction. The noise you have is identical to my previous noise and may be related to crankcase pressure (for example, the oil separator hoses or valve, AKA Crankcase Ventilation Valve, PCV and other names). Good luck.
 

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Discussion Starter · #9 ·
Thanks for all of your input, fellas. I was the Oil Separator (and when you ask someone in Autozone for a price qoute, their heads explode).

It wasn't the separator itself though, the hose leading from the dipstick branchoff to the bottom of the separator was completely severed. I replaced the hose with fuel hose and it runs like a dream now.

Now on to the other issues...

Thanks again folks!
 
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