Subaru 1998 Impreza Owner's Manual page 251

Rubber gaskets
HG0115
4. Put the radiator cap back on and tighten firmly. At this time, make
sure that the rubber gaskets in the radiator cap is correctly in place.
5. Start and run the engine for more than five minutes at 2,000 to
3,000 rpm.
6. Stop the engine and wait until the coolant cools down (122 to
140 F [50 to 60 C]). If there is any loss of coolant, add coolant to the
radiator's filler neck and to the reserve tank's "FULL" level.
7. Put the radiator cap and reservoir cap back on and tighten firmly.
B 2.5 liter models
1. Place a proper container under the drain plug and loosen the drain
plug.
Reserve tank
Air vent plug
Drain plug
HS0179 HG0353
10-18