The metal coolant pipe that is hidden under the exhaust manifold of the 4 cylinder red blocks and connects to the heater hose at the firewall the water pump . These pipes corrode and rust over time, from inside out. The pipe should be replaced.
Volvo 240 1975-1993 NO TURBO
Volvo 740 1985-1991, 8 VALVE NON TURBO,
Volvo 760 1983-1990, 8 VALVE NON TURBO,
Volvo 940 1991 . NON TURBO.
Volvo 960 1992-1995 8 VALVE NON TURBO