Lexus GS300 1998 Owner's Manual page 326

When the engine overheats
Pull safely off the road, stop the vehicle and turn on your
emergency flashers. Put the transmission in "P" and apply the
parking brake.
A: If steam is coming from your engine:
Turn off the engine. Leave the hood closed until there is no
sign of steam or coolant. Your engine could have been
seriously damaged already. Call your Lexus dealer for
assistance.
CAUTION
To help avoid personal injury, keep the hood closed until there
is no steam. Escaping steam or coolant is sign of very high
pressure.
IN CASE OF AN EMERGENCY
313