I decided to change the coolant on my little Suzuki Jimmy 1.5L (M15a), it hasn't been changed in over 2 years. The engine has never overheated and the temp gauge is always rock solid at around 185F when warmed up. On the workshop manual Suzuki recommends running the engine up to operating temp, draining the coolant and then fill again and repeat 2 - 3 times to flush it out. The problem is the engine get's to operating temp but the coolant doesn't flow through the radiator, and the radiator pipes are stone cold. I tried after driving on the highway for an hour but when I drained the coolant it was ice cold. It's like the thermostat is stuck closed but the engine does not overheat. The heater core works fine though. Any ideas on what the problem could be, I can't flush the coolant because what I drain / add to the radiator doesn't seem to actually get to the engine?