Lexus 2016 GS350 Owner's Manual page 531

When adding engine coolant (GS350/GS200t)
■
Add coolant in accordance with the following procedure.
Remove caps A and B.
1
Add engine coolant through the inlet of cap A up to the "[AR/GR] B" line, and then
2
install cap A.
Add engine coolant through the inlet of cap B until it is full, and then install cap B.
3
GS200t only: When installing cap B, apply coolant to the O-ring on the end of cap B.
Cap A
1
Cap B
2
"[AR/GR] B" line (Target fill line)
3
GS350_200t_GS F_OM_OM30E86U_(U)
7-2. Steps to take in an emergency
GS350
531
GS200t
7