So I had a strange coolant loss issue on my RWD IS250 where the overflow bottle kept getting low and then I would get air in the system. Then one day I found coolant spraying out of the radiator cap itself and overflow bottle empty and coolant a bit low. So I replaced the radiator cap and topped up coolant and topped up the overflow bottle to the MAX line which is below the actual written word FULL. After that I've been driving around for a while now and the level in the bottle didn't go down straight away and I've done significant amount of driving since. But today after good few weeks of driving I checked the bottle level on cold and the level wasn't at full. It was just below the middle.

I have no visible leaks, oil area looks clean and no sign of any mayonnaise like substance. Could I still have a leak somewhere?

 

Do you ever notice a sweet maple syrup kind of smell on the outside of the car, shortly after shutting it down? That would be a prime indicator that you are still losing coolant somewhere.

 

The level will never show to the full line with a cold engine. Sounds like your problem was solved by the replacement cap.