Hello everyone. I recently purchased a Lexus GS 200t and am trying to find the cause of the rattling. The sound is only audible outside and when the engine is cold. When it warms up, it goes quiet. It is heard when driving slowly, after stopping it still makes noise for a while and goes silent. The exhaust system seems to be ok. Maybe someone had such a problem before?

 

Loose heat shield?

 

unfortunately not...

 

I would post this over in the IS forum if I was you. Not many GST's here. I remember seeing something about this over there, but don't remember what it was.

 

Is there any change to the sound when engine speed is up or down? How about when the ac is off or on or if the transmission is in park vs. neutral vs. reverse? It initially sounds like exhaust/ heat shield rattle.

 

Also how many miles? I remember the IS Forum saying it was something like air vacuum , some kind of valve leakage. A few owners had this problem pop up. Some were way louder than your sounds.

 

Yes, sound changes a little with engine speed, ac on/off - no difference, it's starts rattling after while car starts driving. On neutral/park - no sound. It's hard to find, because after a less than minute it stops rattling. I will try on IS forum
Mileage: almost 95k miles

 

@Pacmanx - On a turbocharger there is something called a 'wastegate' that controls the boost pressure by bypassing a controlled amount of exhaust gas from contacting the turbocharger's turbine wheel. The operation of the wastegate is controlled by a vacuum regulator. Under typical operating conditions more throttle activates the wastegate via the vacuum regulator which in-turn controls the wastegate The wastegate has a flat round or slightly oval shaped valve disc plate that opens and closes against a passageway that redirects a portion of the engine's exhaust flow for possible use by the turbocharger to spin-up the turbocharger's turbine wheel.

When this valve disc plate is closed (offering no boost pressure to the turbocharger from the exhaust) the valve disc plate naturally sits flush against its valve seat. However, when the wastegate valve disc plate is slightly open - likely during a period of engine warmup or under only a partial load (i.e. light throttle) - the wastegate's valve disc plate has a tendency to rattle or bump against its seat, making a rattle noise. Under a heavier load (i.e. more throttle) the wastegate's valve disc plate is opened more and therefore it is not likely to rattle.

There is also a rod attached to the wastegate mechanism that sometimes can have a bit of extra slack, which can be the cause of a rattle. Some rods are threaded and have an adjustment nut that can be used to take out some of the unnecessary slack, if needed. Oftentimes exhaust heat will expand turbocharger components and that helps to quieten a rattling turbocharger part.

Hearing the wastegate's valve disc plate, or its attached rod, rattle under the conditions you describe is actually quite common and there is absolutely nothing to worry about because there is nothing wrong with your engine or the turbocharger.

I hope this helps!