Lexus 2012 RX450h Owner's Manual page 757

Coolant (RX450h)
The coolant level is satisfactory if it is between the "FULL" and "LOW"
lines on the reservoir when the engine and hybrid system are cold.
Engine coolant reservoir
4-3. Do-it-yourself maintenance
Reservoir cap
"FULL" line
"LOW" line
If the level is on or below the
"LOW" line, add coolant up to the
"FULL" line. (P. 933)
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