5/8″ (16mm) HPS High Temperature Reinforced Silicone Coolant Cap. 5/8″ is the ideal size to block off heater hoses.
SILICONE COOLANT CAP, HEATER BYPASS 5/8″ (16mm) HPS
$25.50
Radiator Hose Set, 83-85, 12A, Silicone
Water Pump Gasket, 04-08 RX8
Radiator Hose Set, 04-11, RX8, Silicone
Radiator Cap Neck, 86-88, Without Over Flow Tube
Sorry, this item has been discontinued by Mazda.
You can use the radiator cap neck with over flow tube N326-15-17YA and cap the tube with a 8mm cap, which you can order here
Water Hose, RX8, Thermostat Cover to Tank / Upper
Radiator Cap, 84-85 SE and + All 79 and before