Hey guys - have done a ton research here and other places and wondering if any lurkers here might have an answer,

First: 2007 GX470 with 63k miles

On some 'cold' starts (and I use that term very loosely, because it never really drops below 40 degrees here), when the engine has sat overnight, and when I shift into reverse (never Drive, just Reverse) and stand on the brake I get a knock. I don't hear it in Park. Not valve clatter like on my german cars while the oil gets routed to the lifters, but instead a loud, startling deep-down knock that sounds like BAMBAMBAMBAMBAM. Then it goes away. Put it in neutral and the revs rise and it's gone. Put it in Drive and nothing there. Just lasts for maybe 5-10 seconds, but MAN is it loud. BAMBAMBAMBAM! Like someone hitting a 2x4 on the block or tranny housing.

Once I'm past that 5-10 seconds it won't do it again all day. Just after a "cold soak". And perhaps 5-10% of the time.

There is a lot of examples with this motor of what some call "piston slap". Don't know if I have it - and I suppose it might get worse (to the point where I hear it) when the engine is cold and under load (in gear), but I don't get it in Drive. Just Reverse.

Anyone? Want to make sure I address before warranty dies!! And if possible want to go to the Lexus with a specific thing to look at as we all know techs are miserable at replicating noise... Thank you all.

 

I've had this too with my 2006, complained about it with Lexus, they couldn't make it do it. I get it occasionally but it doesn't seem to bother anything.

Sign me up as needing an explanation as well.

 

"...complained about it with Lexus, they couldn't make it do it."

And there it is, Blair. haha.

 

I have 80k on mine and it's been doing this since new. Not saying it isn't a "problem", but I've seen no functional impact yet.

 

Stiles - Yeah I agree - nothing seems to get worse but it's just such a loud, non-normal knock - and an infrequent enough one that when it does happen it freaks me out. Will continue to do some more research on piston slap and see if that's what we're dealing with (but I'm not actually sure it is)...

Anyone else?

 

I have experienced the same in my GX on cold mornings, maybe not as extreme as you are describing but certainly an unusual noise when in reverse after a cold start.

I find if I let the car idle for five or ten minutes it eliminates the noise completely, letting the engine warm up a little before driving is a good practice on cold mornings anyway.

 

Agree MS - if I let mine sit for 30 seconds it won't do it - it's just that rare gotta-hop-in-and-MOVE moments when I get it. The usual 30 second idle never elicits it. Weird trucks.

Would like to know what it is, nonetheless - so if anyone else has experienced this or would posit a guess please feel free

 

2006 with 60K miles, purchased used 6 months ago.

Mine does the same thing. I live in Southern California and it seems to do it when the morning temperature is around 60 or below.

I haven't been able to identify the issue. If you search Toyota V8 knock on cold starts, there is a list of threads from Tundra to 4Runner owners.

There was one thread where OP claimed he fixed the issue by replacing the fuel damper. I tried this (around $100 from dealer) to no avail.

Many claim this is a piston slap.... I'm not 100% I buy into this. I've owned two Tundras before (2000 and 2004) and neither one ever made this noise. The only difference is that my Lexus has the VVTi engine.

Are you sure it doesn't make the noise when in D? Most people describe the problem to only arise when the transmission is engaged (either R or D).

 

My latest theory is that it's related to fast idle (at cold start). In this situation, it's idling much faster than normal, placing a lot more load on the transmission. I wonder if what we're hearing is some sort of a pressure release system in the tranny? Perhaps timing getting retarded by the ECU to lessen load? Would love to know. Very curious. But, it's common enough, and these transmissions and engines seem to last long enough, that it doesn't appear to be causing damage whatever it is.

Also, I've only ever heard it in reverse.

 

Agreed... I've read many threads on this topic and no one has claimed that this symptom led to any type of engine damage.

The one thing I was thinking about is that the only difference between idling in P or N versus in gear is that the torque converter is absorbing the energy. Perhaps the fluid in torque converter is making the noise when cold? I'm not an expert but if we are suffering from piston slap issue, shouldn't the noise be apparent even if transmission is not engaged?

Regardless, this noise seems to be just a nuisance and not indicative of a major problem down the road....