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Discussion Starter · #1 · (Edited)
Good day! First time posting, but have lurked some. I'd like y'alls thoughts on what could potentially be broken.

After a recent trip, I started hearing a noise that I couldn't place. After 20 mins of more driving and getting off the interstate, the sound was more evident especially when accelerating. I pulled off to an autoparts store, and checked oil level (among other things). I was low. After about a 1.75 qts, oil started showing up on the dipstick. I had been about 7000 since the last oil change, so I was due (I change every 5000 miles with Castrol Edge or Costco's Kirkland). I kick myself now for not changing it sooner. I'd have seen the lowered oil level.

EDIT: The check engine light nor the engine oil did not come on. The auto parts store scanned as well, but there were no codes (with their basic scanning tool).

I drove back (about 2 hours worth of driving), trying to keep RPM under 2K. We listened around the top of engine with a long screwdriver, and there was some noise with the belt tensioner. So, I went ahead and replaced that (plus belts were still original). It made things a little quieter overall, but didn't reduce the knocking sound.

So, I'm at the point where I'll probably call a couple shops around to see who can take a look. Any thoughts on possible culprits to try to get some initial quotes?

Some background and observations:

  • Sound seems to be most evident when giving light/partial throttle, starting around 1500 RPM up to at least 3000 RPM. Sound does not occur when releasing throttle at those engine speeds.
  • Sound occurs with clutch in or out.
  • Belt tensioner, serpentine belt, and water pump belt were replaced yesterday.
  • I'm not sure where the 1.75 quarts of oil went. I didn't see leaking from the oil pan plug and oil filter, nor any stray oil on the underside panel cover. Maybe I'm just burning oil?

I did an oil change yesterday, and noticed the oil was glittery. I took apart the oil filter, and there's metal shavings in almost all of the pleats, so things aren't looking great. The shaving don't appear to be magnetic. Example below:
Blue Azure Liquid Aqua Material property

Blue Hood Azure Line Road surface

Here's a couple videos of the sound, from inside and outside.

Outside/parked (slow sustained rev up to 2000 RPM):

2013 Mazda 6i Grand Touring - 2.5L I4 Auto
345 Posts
Sounds like you have a misfire. Have a look at the spark plugs to see what's going on inside the engine.

Rally Racer
2004 Mazda 6s Wagon ATX
4,443 Posts
I don't hear the misfire (exhaust sounds smooth) but I definitely do hear the knocking.
If you added 1.75 quarts before it started showing on the dipstick you were likely more than two quarts from the low mark. That means three quarts from full. I think you already know what the verdict is. :confused: Unfortunately the oil light is only there to inform you officially that is is dead.

A connecting rod journal will be loudest under load (accelerating) if the tolerances are too large for hydraulic cushioning.

That is a fair bit of metal for one cycle and you mention it is glittery in addition to what was trapped by the filter.

Now would be one of the few times I would recommend an oil additive. A Lucas high mileage product perhaps, or 20-50 oil, If it improves slightly then it is likely a bearing(s).

Keep the rev's down and short shift it until you can find a replacement or service.

My 2-cents. Good luck.
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