@Gville350
Add this to OP. Squeeze the top radiator hose. If it collapses completely, the system is free of pressure and you can safely remove the radiator cap.
If it does NOT collapse, allow the engine to cool more or you are at risk of being burned by hot coolant.

Thanks!

 

I just happened to read this while on a trip away from home lmao. Now I'm anxious to see how my radiator cap looks...Got an '06 IS350.

 

GS450h (S19), same parts there (thrermostat housing / cap / etc). OEM cap lasted >200k km. Replacement cap (OEM) - I just popped the hood today, found the level low and the cap... well, I'm taking apart the housing now to find where the last piece managed to go. Totally calm and collected

edit: estimated ~150k km, I was gradually "losing coolant" from somewhere (by gradually I mean two centimeters in the expansion tank per year - a.k.a. in the "am I just crazy" territory). Did a check-up, the coolant level had crossed the "low" threshold, undid the cap and you know what followed.

 

Just a rule of thumb that I haven’t been following lately but the thermostat and radiator cap should be replaced every 100k miles regardless of make/brand of car. It’s one of the few rule of thumbs for replacement parts that has merit plus the parts are cheap.

 

Does anyone know of any aftermarket, or other OEM radiator caps, that are all metal that work well on the IS 350?

I rather not buy the original Lexus plastic one if it fails in this short of a time period.

Thanks,