My car randomly started to make some weird noise when I started it in the morning. I took it to the dealership, and they couldn't find anything, and now my engine light is on. The Toyota dealership was not able to find any problem, and the car is in the shop for another day. I also have a Lexus HS 250H, and it started making this noise in the morning. After the engine heats up, it's gone. I live in Minnesota, and it's been freezing right now and wondering if that could have made any difference.
Severe rattling that goes away within a minute is typically a head gasket. Codes may or may not be present but are usually misfires on changing cylinders. A Borescope inspection with a quality two view tool when cold with the radiator manually pressurized is often definitive. Traditional hg checks like leakdown, compression, coolant loss or combustion gas in coolant are not typically useful as these engines seal quickly when started.
If it's really happening randomly / sporadically, not consistently, there is also another issue it can be, nothing to do with the head gasket; it can be water that condenses in small passages of the intake manifold while the engine sits in the cold, as was addressed in this TSB. Seems more likely to happen if the last use of the car, before sitting in the cold, was brief and it didn't fully warm up. For a while, Toyota offered a revised intake manifold where those passages were a funnier shape less likely to spurt the water out, but that didn't seem like a silver bullet, and even with the unrevised manifold it seems you can mostly avoid it just by making an effort not to have brief, non-warmed-up uses of the car before letting it sit in cold weather.
The car is in the shop for the second day. Let's see what they say. Looks like they still need more time to find the problem. I am shocked that the dealership can't figure out the issue when they have a code. I am sure this is one of many cars reporting these code-related issues. This dealership services 150 cars a day.
Thank you, RJP, for your suggestions. I am a teacher and don't know much of the technical stuff. They say they can't find anything, and the code is generic. Their recommendation is to change the spark plugs. I changed them once at 120000, and now I am at 180000. They are asking me to try putting some seafoam in the gas tank if that helps. I will keep you posted. Thanks again.
