V8 knock on cold start? Try this $34 fix first

[07V8]

Nothing wears in these engines. Someone on iH8mud tore one apart with over 300k on it. The cylinder walls still had honing marks and all critical GD&T was within factory specifications.

These engines are absolutely bombproof. They're also noisy when cold - simple as that.

 

[cseaman]

has anyone here who (maybe errantly) thought they had the exhaust manifold tick/failure replace this part and actually have it go away?

 

[duffdog]

Lol it wasn't happening before, and now it is, that's not how piston slap works, I would have heard it the whole time I owned it.

I don't think its as simple as that. The sides of the pistons on the newer 2UZ motors (05+) have a plasticized coating that wears off after some arbitrary number of miles and makes the piston looser in the bore. I know this because I took my entire engine apart when I blew it up and could compare the different piston designs from different 2UZ years. You could literally see where the coating was worn off and how it would make the piston slightly smaller. It is my opinion that this baked-on coating is responsible for the change in piston diameter over time and that is what is causing the slap that we all hear on cold mornings.

 

[Bob22222]

Mine is not very loud. I can only hear on cold start in the echo chamber of my garage upon placing it in reverse or drive. Summer or winter same thing. Ambient temperature seems to have no effect. In attempt to describe it I'll say it sounds like a loud ignition wire leak (not) or a banging valve lifter or something else not yet cushioned by full oil pressure and flow. Every now and again I think about it and then decide ignoring it is most likely a good choice. I do think it might be emmissions related?
BTW, In the old days that's what a loose wrist pin sounded like as it allowed the piston to begin slightly Contacting the head. And if you ignored it soon followed by the rod bearing on that cylinder soon going south. And...
I'm glad we don't have those problems and my advise would be to try and not to create them in your head. Much ado about nothing, as a fellow named Bill once said?

 

[4runner206]

I don't think its as simple as that. The sides of the pistons on the newer 2UZ motors (05+) have a plasticized coating that wears off after some arbitrary number of miles and makes the piston looser in the bore. I know this because I took my entire engine apart when I blew it up and could compare the different piston designs from different 2UZ years. You could literally see where the coating was worn off and how it would make the piston slightly smaller. It is my opinion that this baked-on coating is responsible for the change in piston diameter over time and that is what is causing the slap that we all hear on cold mornings.

thanks for all the help and advice, it ended up being a bad alternator bearing it was a weird ass sound, very slight grind very hard to describe haha, but with time it got bad enough to actully find the the culprit. now it sounds super smooth at all times, i even had some cold starts around 20degrees to test it! now to get this 4low issue to get worked out!!!!

 

[RPC]

Old thread I know, but I'm still trying to solve this issue.

Replaced the damper with the OP's PN, we'll see if it does the trick.

 

[Hiker865]

My 2006 with 46k is doing this on cold starts.

My question is......do I NEED to replace this part or is it ok to leave it as is and deal with the noise on cold starts? It isn't bothering me as it goes away as soon as the temps warm up but I don't want to harm my 4runner.

 

[Ric232]

My 2018 w/ 33k miles (V6) has a similar noise on cold start. Goes away after about 5 mins of run time. I can hear it both inside and outside the vehicle. It's not very apparent when I first start the vehicle because of the fast idle. It becomes more pronounced as the idle slows down in the warm-up cycle. But after 5 mins or so, it's gone.

 

[tylrdvs277]

Sorry to wake up this thread, but I may have the same issue. Only on the first start of the day (as cold of start as you get in San Diego). Throw it in reverse and I get a knocking like this. Back up the driveway, drive off, and as soon as I get any speed it stops. Also doesn't happen if I just let it warm up in park. Does this sound similar?

 

[dangbt]

My 2018 w/ 33k miles (V6) has a similar noise on cold start. Goes away after about 5 mins of run time. I can hear it both inside and outside the vehicle. It's not very apparent when I first start the vehicle because of the fast idle. It becomes more pronounced as the idle slows down in the warm-up cycle. But after 5 mins or so, it's gone.

I have a V6 with 240k and have similar problems. Did you ever figure out what it was?

 

[rgwest61]

Late to the Party

I know this thread was started many years ago, but I just came across it. I have a 2009 4Runner 4.7L V8 with 195K miles, and have been experiencing this issues for the last 2 years. Several repair shops have been unsuccessful to determine the issue. I want to make sure I order the correct part for my model. Anyone know the OEM part number?
Thanks.

 

[AuSeeker]

I know this thread was started many years ago, but I just came across it. I have a 2009 4Runner 4.7L V8 with 195K miles, and have been experiencing this issues for the last 2 years. Several repair shops have been unsuccessful to determine the issue. I want to make sure I order the correct part for my model. Anyone know the OEM part number?
Thanks.

It's a different part number for different year models, for your 2009 it's 23270-50011 , here's a link to where I got this part number and most likely or close too the best price you're going to find for OEM, also Toyota has a 25% discount going on right now for a few more days until 12-02-25, not sure if it applies to all online Toyota dealers but I think it does at this dealer, you might not see the discount until checkout..

Part link

23270-50011 Genuine Toyota DAMPER Assembly, Fuel Pr)