Volvo Repair: 1992 Volvo 240 overheating, clutch fan, 1992 volvo 240

Question
The car temperature gauge in my 1992 240 goes into the red until I turn on the heater, then it goes down again.  I changed the thermostat but that didn't fix the problem.  I was told that it could be caused by poor air flow across the radiator due to the outside of the radiator being clogged with dirt and bugs.  How do I clean the outside of the radiator.  With a hose and water?
Thanks

Answer
Hose and water is fine but air hose would be better.
Since you've already replaced the thermostat, you've isolated the condition to 2 possibilities, restricted radiator or bad clutch fan.
Freeway overheating usually is radiator.
City overheating usually clutch fan.
Then depending on amount of miles could even be both.