Lexus RX300 Manual page 266

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.
Engine coolant selection
Your coolant must contain ethylene–glycol antifreeze. In addition
to preventing freezing and subsequent damage to the engine, this
will also prevent corrosion. Further supplemental inhibitors or
additives are neither needed nor recommended.
Read the antifreeze container for information on freeze protection.
Follow the manufacturer's directions for how much to mix with
water. The total capacity of the cooling system is given on page 243.
We recommend 50% solution be used for your Lexus, or a sufficient
quantity to provide protection to about –35_C (–31_F).
NOTICE
Do not use alcohol type antifreeze or plain water alone.
SPARK PLUGS
62R031a
Your engine is fitted with iridium–tipped spark plugs.
NOTICE
Use only iridium–tipped spark plugs for your engine
performance and smooth drivability.
ENGINE
251