I bought a used '99 RX300 FWD/2WD a while back and noticed at times I get a rattle out of the engine... it's like a clattor... like an old V-8 engine with all rocker arms a bit loose. It's that loose rattle that's fast, meaning it doesn't sound like it only makes an audible sound on one cylinder or anything.

I've Seafoamed the engine, rant AutoRX, watched the oil, changed the PCV, and checked the engine up and down. It all looks good... oil is clean, Auto-RX didn't put out any black gunk after it's "cleaning cycle", and there doesn't seem to be much of any carbon build up in the engine... Seafoam produced very little smoke and I've pulled some of the plugs... they look great.

As far as performance, I'm getting great mileage (22mpg last time I checked), the engine runs great, pulls hard, never hesitates, idles smooth.... it all looks good except for this freakin' rattle under the hood. It doesn't do it all the time... it's smooth and quiet from a cold start up, but once it gets warm, espeically on a hot day, the gurgle/clattor/rattle is pretty pronounced. On level ground I can accellerate slowly with no rattle, then accelerate a little more with some rattle, have the rattle get louder as I push on the gas more, but then I can kind of snap the gas pedal down and get a wrrrrrrrrrrp out of the engine as the sounds seems to clear up... under strong load it's not there.

I've switched the tranny mod the ECT/Power and with lighter/easier shifts, the clattor rattle is much less. In the mornings on the commute to work it's not even there. On hot days driving home it's there in spades at the end of my commute.

So, does anyone know what could be causing this? Noisy injectors? Detonation? A bad knock sensor? A worn/stretched timing belt? Other? Has anyone had any experience like this? It seems pretty minor, but totally annoying and embarassing when I drive though my neighborhood slowly up a slight grade with 'clackity clacktiy clack' coming out from my shiny black Lexus.

We also have a 95 ES300 with essentially the same engine, and it doesn't make any sounds... and it's old and dirty and puffin' a little blue smoke out the back, but quiet as a whisper.

Any thoughts? Anything to check? The CEL is not on. I tried my code reader to see if there were any internal codes... none. Everything looks good except for this strange noise. Any imput is appreciated.

Thanks in Advance!!

 

It's really tough to say. I can think of things like lower suspension arm that is loose and clanking that would do this.

Other things such as lifters, torque converter (you don't want that). One that may be the culprit is an engine mount and these do make a similar sound to the one you are talking about, but not necessarily under load.

Do you hear the sound after driving around and just before you turn off the vehicle?

 

Another thing it could be is the Air conditioning compressor. Ours made rattling sound until I tightened the drive belt. Try turning the climate control off when the rattle occcurs and see if it goes away.....

 

I was also wondering if it might be this piece here. This part of the exhaust was known to crack on early RX300s and it did on mine and my uncle welded the piece shut. Made an odd farting-like noise, but only noticeable at lower speeds.

 

Hey Guys, thanks for the quick reply. Yeah, I know Lexmex, it's a shot in the dark to diagnose via the web with just some rough symptoms... I was hoping maybe someone had the same thing happen and had found the culprit. I have ruled out the suspension and exhaust as being any of the problem, for when it does the strange chatter, it's directly tied to the gas pedal and load on the engine, plus I can vary the sound with the amount of gas I give it. What it acts like is some horrendus pinging, but putting in higher octane fuel doesn't help/change it, and it only does it when the engine is hot on a hot day.

I have tried your suggestion, Thomas, with turning the A/C on and off to see if I get any variation in the sound... and I don't. When the chatter isn't there, the A/C doesn't affect it. When the chatter is there, the A/C doesn't affect it.

I've been around cars (inside and out) most of my life from street to strip and have seen and diagnosed a lot of symptoms, but this one is strange. It's definitely not a torque converter rattle (I've heard that sound before), and the worse part is it isn't consistent. On the LOC board a guy suggested it might be carbon build up in the combustion chamber causing predetonation, but I've Seafoamed the engine and it looks clean when looking down the spark plug hole onto the piston.

What ever it is, it doesn't seem to affect the performance nor gas mileage, and when it's not making the rattle/clattor/clammor, it runs, drives, and rides wonderfully. I just don't know what is causing the sound. Could something be causing it to predetonate so badly at times?

BTW, Lexmex, my wife says 'hey neighbor', for she's from Cuernavaca. Ah, what a gorgeous place!

 

Engine mount? Put the gear on N. Gas it and brake. If the engine lift too much, it may make some noise and rattle. Just a guess, GL.

 

Wow, really weird, would make me real nervous about the valve train under the cams....Maybe a broken spring....

 

Yeah, Thomas, that's what I'm nervous about. The only thing that makes me think it's not something major like a broken spring is that it 'self heals' when the engine is cold and on a colder day. I mean, it could be the broken spring shifting around and making noise at times, but then not at others, but this sounds is showing up with a solid pattern, only once it's warm on a warm day. Plus a broken/crushed valve spring should give the chatter at idle and no load revving of the engine (which is smooth and quiet) along with reduced power and fuel economy since I wouldn't get full sealing on one of my cylinders. I haven't run a compression check, I think they are okay.

In knowing the assembly of the valve train (there are some good assembly pics here... and a very intersting visual of oil gelling: http://www.tegger.com/hondafaq/sludg...ng_sludge.html ), and knowing that the cams spin over valve buckets that use shims for the adjustment mechansism, I'm thinking maybe I've got some slop in the valvetrain and as the engine/oil heats up, the oil thins out and I get the chatter. I don't know... just a theory.

I thought about what Franics said, and I checked the engine mounts. They look good. I've had engine mounts fail on other vehicles... and that usually results in a 'clunking' sound as the engine shifts load based on acceleration. The mounts see a little too much weight from the engine to really rattle, but it was a good thing to check! Thanks.

So, I guess my options are to either keep an eye on it, or take it to a shop, but then with symtpoms like these, it's not something that can be diagnosed on a scope... and the other diagnostics are 'by ear', and unless it's a familiar sound, we may start with the "we can try replacing this and see if it fixes it" game. That's not something I like to do.

I'll keep an eye/ear on it... thanks for everyone's input. Hopefully it's something minor that just sounds worse than it is.

 

I have the same problem with my 2006 RX330. I brought my car to the dealer but they checked it but could not find anything because the problem didn't happen at the time I brought it in. It's intermittent. I probably have to wait until summer time when it happens more often on hot days and bring it back to the dealer.

Does anyone find out what the problem is?

 

Welcome to the Club.

I understand you say it is intermittent, but when precisely do you hear the noise, when starting up? On the road at a given mph? When coming to a stop?

 

There are rattles and there are rattles ...

First thing is to determine the source ...

I had one, which I kind of narrowed down to the front radiator area. I could reproduce it by slapping the little horn in the front. Finally, I traced it down to a loose mounting screw of the hood release mechanism. The bolt head was behind a structure support so I could never see it directly.


So try to narrow the source down . there are too many things in the engine bay that can produce rattle and it may have nothing to do with the engine itself.

Salim

 

Piston slap?or cracked piston? I heard this in a 92 mercury topaz once.But that was piston slap in that car.

 

Thanks for your reply Lexmex, I have a similar problem like what blkongray described at the begining of this thread. I normally hear the rattling noise when the engine is hot especially on warm days and driving at slow speed. I heard the noise and I stopped and switched to neutral mode, pressed the gas pedal again but didn't hear the noise. So it happens only in driving mode. I've never heard the noise within the first 30 minutes after started. that's why I said "when the engine is hot". I also tried to turn the AC on and off but no differences. any idea? Thanks

 

It might be a combustion issue there. I know what you are talking about because I also face this on warmer days in Mexico City.. I have been in a few vehicles, but not mine, where a P0420 error will be triggered under one of these scenarios and I know the combustion must have been crap to throw such a catalytic converter error (nothing wrong with the cat, just the combustion), because only a combination of Pemex gas and a hot day at altitude will do that.

If you get cooler air, thus more oxygen, then the combustion will of course be better and things will be smoother.

You might not hear it in neutral or stationary as much given that the air flow and fuel flow is decreased at that point, but under acceleration that hot air going into the engine could very well cause the situation at hand.

Unfortunately, I don't know that there is a fix for that offhand for that, probably something I have to take a closer look at on my own when I hear the noise again.

 

I have had other cars that had weird rattles that came from broken catalytic converters. The honeycomb can break into pieces and make some strange sounds. Sound will change with the RPM making you think it is a motor issue. Worth a shot. A mechanics stethoscope should help narrow it down.