Toyota Lexusc Owner's Handbook Manual page 663

ENGINE
If the coolant level drops within a short time after replenishing,
there may be a leak in the system. Visually check the radiator,
hoses, engine coolant filler cap, radiator cap and drain cock
and water pump.
If you can find no leak, have your Lexus dealer test the radiator
cap pressure and check for leaks in the cooling system.
CAUTION
To prevent burning yourself, do not remove the radiator
cap when the engine is hot.
NOTICE
Do not use plain water alone.
644
Coolant type selection
Use of improper coolants may damage your engine cooling
system.
Only use "Toyota Super Long Life Coolant" or similar high
quality ethylene glycol based non- silicate, non- amine,
non- nitrite, and non- borate coolant with long- life hybrid
organic acid technology. (Coolant with long-life hybrid organic
acid technology consists of the combination of low phosphates
and organic acids.)
"Toyota Super Long Life Coolant" is pre- mixed with 50%
coolant and 50% deionized water. This coolant provides
protection down to about -35_C (-31_F).