Cold start knock
 

So this summer my car started making a really strange knocking sound at start-up/cold start. It sounds like a knock however it only happens for half a second then goes away and the engine sounds absolutely normal. The sound is present ONLY if the car has been sitting for at least a day, so I am guessing it has something to do with the oil.

The car runs fine otherwise, no smoke coming out the exhaust and no other strange sounds coming from the engine.

Also there's no mods done to the engine other than a K&N air filter.

I ran the car during winter and it didn't make this sound, so i doubt it's due to temperatures.

The car has received regular oil changes at around 3500 miles. It has been running Motul 300V 5w40 for 40.000 miles.

Here's a link to how it sounds from inside the cabin:

https://youtu.be/MrLvOKbJcII

Have your checked your oil level?

Yeah, oil level has been full ever since the last service, no oil consumption whatsoever.

Has it been doing this since your last oil change? Could be a few things... assuming you don't beat the engine to absolute death regularly, it's likely not worn parts or anything.

Could be your valve lifters.
How about your oil filter, is it OEM spec or something else?

Last oil service was in March, about 3000 miles ago. I first started hearing this sound in July, so i'm not sure the two correlate. One notable thing from my last service is the fact that the shop overfilled my pan with oil, not by a lot, but they did overfill it.

And no the car does not get beat on that much, it has only seen a track day so far this year.

Oil filter is an aftermarket Mann oil filter, the skinnier, elongated type.

Oil overfill could be bad from what I've read in the past, but that depends on how much they overfilled. It can actually reduce the oil flow to certain parts, which could certainly cause the sound you describe. If nothing is new about the oil filter or oil weight used, I would doubt it's the culprit. But you could try a lower weight oil for better flow on your next oil change and see if it stops. In general, it might be worth changing out your oil with your situation to see if anything changes, because there are very few things that can make that sound other than internals, at least for the quick duration that you hear it at.

Here is a quick writeup about the negative with oil overfill.

https://www.cars.com/articles/what-h...th-oil-433476/

Maybe your oil is too thick?
Toyobaru says to use 0-20.

Or 5w30, which is the recommended grade for heavy usage.

I do agree 5w40 is a step-up, but it has run it for 40.000 miles. I doubt that's the problem

I was planning on going down to 5w30 for the next service. Let's hope the issue goes away by itself.

Yeah I'd report back when you change the oil to a lower grade. The sound is certainly not pleasant, and nor is it doing any good to your internals, if anything it is speeding up wear, so you don't want to prolong that too much.

Good plan - keep us posted - ;)

It's early rod knock. Takes a couple seconds for the oil to pump up and hit the bearings from a cold start. Relying on thin film lubrication until then, and it's when worn journals will be most obvious.

Sorry. Sucks. :(

Probably off base, but I had a bad harmonic balancer on my pickup's straight 6 make a similar sound. Wouldn't hurt to check.