Today on Name That Sound! Rod Knock, Oil Pump, or Flex Plate??

Jordan Owner/Technician Washington Posted   Latest  
Resolved
Drivetrain
2008 Subaru Forester 2.5 X 2.5L (EJ253) 5-spd (TY755)
Loud Noises

Sound starts after about 10 minutes of driving. Becomes louder and louder until ignition off. Hot start results in same loud noise which then immediately quiets down. Clogged pickup tube? Worn Pump? The sound becomes so loud my stethescope can't pinpoint it; I hear it everywhere except accessories.

Please share your thoughts!

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Interesting
Jordan Technician
Nevada
Jordan
 

If you do suspect the flex plate, I have had good results from spraying WD40 onto the center hub of flex plate while the engine is running. The noise will quiet down or go away completely if the flex plate is cracked and rubbing together.

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Matthew Technician
Nova Scotia
Matthew
 

My audio quality isn't great on my laptop but my vote goes towards flex plate as well.

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Jared Diagnostician
Maryland
Jared
 

Have you tried taking the tip off of your stethoscope and just used the hose part? That could move you in a direction potentially

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Helpful
Frank Owner/Technician
Ontario
Frank
 

3/8 hose about 24'' in length has always been my weapon of choice.

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Thanks
Grant Technician
Illinois
Grant
 

How easy is it to disable spark one cylinder at a time on this engine? What is the frequency vs engine speed? I counted 61 knocks in your 10 second video, so about 6 times/second at the given engine speed. Simple math: at 720rpm, there are 360 power strokes per minute. 360/60=6. So if your rpm was about 720 in the video, my bet is a single cylinder power stroke is the triggering event for the…

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Paul Mechanic
Illinois
Paul
 

I like your analytical way of thinking which makes me wonder if a scope is available, he should sync it with ignition and use a knock sensor signal to see if it lines up with a particular expansion stroke? Maybe consult scanner with knock sensor pids to help isolate one bank from another.

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Agree
Grant Technician
Illinois
Grant
 

I feel more like I've gone down the rabbit hole than winning the engine noise game. Camshaft speed is 1 revolution per 4 stroke cycle as well.

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Stephen Technician
Tennessee
Stephen
 

To me it has a clack that more sounds like valve rocker. If you have chassis ear or knock sensor or intake pulse sensor( think FLS). A scope capture of the noise with an ignition sync will help ID if it is crank, cam or single cylinder or other. Just listening sounds like single cylinder. Be aware that rods knock on the intake stroke not the power stroke.

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Troy Owner/Technician
Washington
Troy
 

if that has a chain could it be the tentioner I dont think thats a flex plate so either rod or tentioner would be my guess

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Randall Technician
Pennsylvania
Randall
 

Jordan, The sound seems to be too high of pitch to be rod or main. Also seems to be timed to cam speed and possibly louder on left bank? Rods and mains are usually loudest on cold start before oil pressure catches up. I like using a very long screwdriver to isolate noises, the plastic hand seems to act as an amplifier. Randy

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Troy Owner/Technician
Washington
Troy
 

I had a customer with a 6 cylinder and it was the tentioner that had failed and it sounded like that it just hammered untill oil pressure finaly bilt up maybe yours is not able to build pressure and the guied is just beating against the stop it seems to loud for a lifter, I know not main

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Aaron Diagnostician
Iowa
Aaron
 

I have a GM knock sensor with a magnet on it I use with scope, sync to a cylinder to determne speed and cylinder. I also combine that with cylinder deactivation. Sometimes the knock will disappear and sometimes it will become a double knock as the piston changes direction. You are just looking for a change as the cylinder pressure is lowered.

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Leo Technician
New York
Leo
   

The video you’ve shared is of an FB engine, so that cannot be a 2008 Forester. I presume you’ve verified the oil level is correct? If the level is correct now, then it was most likely dangerously low in its recent history. That is exactly what a failed rod bearing sounds like in these engines. And if it is indeed a rod bearing, you can pinpoint which cylinder it is by scoping cylinder 1 coil…

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Thanks
Tony Owner/Technician
Missouri
Tony
 

That's cool, I will have to try this the next time I have a cyclical noise at a once per 4 cycles rate. I know nothing of Subarus and trust your experienced ear, but I was thinking that noise sounds a lot like a collapsed hydraulic lifter or other valvetrain related clearance issue. One thing I always try on a noise like this is to snap accelerate the throttle and see if the noise increases in…

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Jordan Owner/Technician
Washington
Jordan Resolution
 

Decided to to an oil change thinking there might be a clogged crank bearing oil gallery. When removing the top mounted filter, it was absolutely bone dry; malfunctioning ADV. Replaced with quality filter and oil, sound is gone. Suspect poor quality oil filter interfering with system PSI and causing rod knock on hot runs and starts. Knock is gone for now, customer is happy.

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Jared Diagnostician
Maryland
Jared
 

Fram filter?

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Jordan Owner/Technician
Washington
Jordan
 

White label fleet filter. The kind that just says “FILTER #xxxx”.

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