Lexus 2003 LS Owner's Manual page 377

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 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.
Coolant type selection
Use of improper coolants may damage your engine cooling
system. Your coolant must contain ethylene–glycol type
coolant for a proper corrosion protection of your engine that
contains aluminum components. We have used "Toyota
Genuine Long Life Coolant" in your Lexus vehicle. In order to
avoid technical problems, we strongly recommend using
"Toyota Genuine Long Life Coolant" or equivalent.
In addition to preventing freezing and subsequent damage to
the engine, this type of coolant will also prevent corrosion.
Further supplemental inhibitors or additives are neither
needed nor recommended.
Read the coolant container for information on freeze
protection. Follow the manufacturer's directions for how much
to mix with plain water (preferably demineralized water or
distilled water). The total capacity of the cooling system is
given on page 353.
We recommend to use 50% solution for your Lexus, to provide
protection down to about –35BC (–31BF). When it is extremely
cold, to provide protection down to about –50BC (–58BF), 60%
solution is recommended. Do not use more than 70% solution
for better coolant performance.
NOTICE
Do not use alcohol type antifreeze or plain water alone.
ENGINE
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