Lexus GS300 1998 Owner's Manual page 389

ENGINE
CHECKING THE ENGINE
COOLANT LEVEL
62G004–1
" 1 Reservoir cap
2 Upper line
Park the vehicle at a level spot and look at the see–through
coolant reservoir when the engine is cool. The coolant
level is satisfactory if it is between the upper and lower
lines on the tank. If the level is low, add ethylene–glycol
type coolant.
The coolant level in the reservoir will vary with engine
coolant temperature. However, if the level is on or below the
lower line, add coolant to bring the level up to the upper line.
Use only ethylene–glycol type coolant. It will prevent
freezing and corrosion. Neither supplemental inhibitors nor
additives are needed nor recommended. (For information on
ethylene–glycol coolant, see also "Engine coolant selection"
described below.)
376
3 Lower line If the coolant level drops within a short time after
replenishing, there may be a leak in the system. Visually
check the radiator, hoses, radiator cap, 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.