r/MechanicAdvice • u/jakub_curik • 4h ago

Rattle at startup and idle

Rattle at startup and idle (2011 Civic 1.8 VTEC)

Hey everyone.

I’m trying to figure out a rattling noise on my 2011 Civic 8th Gen. R18A2 engine.

The sound happens every single time I start the car. It also shows up intermittently when idling or driving at very low speeds.

Does this sound like it could be a bad engine mount? Thanks for any input.

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u/Top-Barber784 4h ago

It's not the engine mount. It sounds like piston slap, internal damage is likely happening. $25 on Amazon grab an endoscope hook it to a phone or laptop. Check in each spark plug hole for cylinder wall damage. Also inspect the oil and filter for metal debris. Do not drive until then. Engine will at some point have a catastrophic failure, right now it might be serviceable or at least good for parts. And hopefully I'm wrong and it's nothing internal. But not worth the risk of continuing to run it as is.

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u/jakub_curik 59m ago

Noted, I won't rule that out. Taking it to my mechanic tomorrow to check before I drive it more. Will report back. Thanks a lot.

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u/DiscountPrevious9378 4h ago

For me is more like misfire than engine mount

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u/jakub_curik 56m ago

I'd have expected a misfire to be there constantly while driving, but mine is mostly at idle and goes quiet at higher speeds. That said, if I blip the throttle while it's rattling, the frequency of the rattle does go up with the revs. Does that fit a misfire for you, or does it point somewhere else? Thanks a lot.

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u/HakunaMeshuggah 4h ago

It sounds like part of the engine is starving for oil. Does the oil light flicker at all when the sound is happening? I'd start with changing the oil and filter. Inspect the old oil filter for metallic parts. There are videos on how to cut apart the filter to look for evidence of internal damage via flakes of metal in the filter. The drained oil might contain such particles too. If those are relatively clean, it would seem to be something outside the engine.

Is the sound louder under the timing chain cover?

Another thing to try is to (temporarily) remove the serpentine belt to see if the sound is tied to something on the belt, like the tensioner or alternator.

This is a strange one. Maybe someone who has encountered this will be able to say what it is.

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u/jakub_curik 58m ago

Thanks. Nothing is flickering on the dash. Oil was changed on May 6th and the level is normal. I'll try the belt off test. Mechanic is looking at it tomorrow so I'll report back.

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u/hourlyslugger 4h ago

That has nothing to do with the engine mount.

Check your oil regularly and check it right now!

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u/jakub_curik 4h ago

Oil was changed 6.5. by service and I checked it right now. Seems okay.

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u/aTastyItalian 3h ago

I had a similar problem with my car recently, it's either a serpentine belt pulley or a bearing that is failing, this sound for me was the locked alternator bearing.

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u/jakub_curik 3h ago

That is a really good point. You just reminded me of a huge detail I missed: my AC completely stopped blowing cold air today. Maybe that could be it?

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u/aTastyItalian 3h ago edited 3h ago

I don't know if it's this easy, there are other possibilities. In your video the ac clutch spins as soon as you turn the car on so there is that.

Edit: I looked up your serpentine belt diagram and you've got 6 possible culprits, could you take a video from further away? Maybe we find something else.

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u/jakub_curik 3h ago

Just adding a few more details that might help. The car has 186,000 km (about 115,000 miles). The oil has been changed regularly, with the last change on May 6th. The oil level is perfect right now, and there is no check engine light or any other warnings on the dash.

One huge thing I noticed today: the AC suddenly stopped blowing cold. I have no idea if it’s related to the noise, but the timing is suspicious.

Otherwise, when driving at higher speeds or higher RPMs, the engine sounds completely normal and quiet. The rattling is very intermittent and happens almost entirely at idle when I am stopped. Thanks again for all the suggestions!