Engine Cooling problem
1990 Volvo 240 4 cyl Two Wheel Drive Automatic 175000 miles

my 1990 Volvo is inconsistent with its overheating...need to turn on heater to cool down the car...mechanic says he thinks the water pump and thermostat are fine and believes that the radiator is bad...hot at the top and cold at the bottom...tested with a digital thermometer....can a solvent be used to "clean out" the radiator?...does the solvent need to be under pressure to work...is it worth trying?....