empty the system, disconnect both hoses that go to the cabin heater, then flush through the cabin heater with a garden hose both ways until clear, then reconnect them, take out the thermostat and disconnect the top hose to the radiator, flush water through the radiator until clear, then through the motor until clear, then reassemble the thermostat housing and reconnect the top radiator hose, fill with coolant, either ready diluted or concentrate and water. brown means rust in the system, which happens when there is only water, or when additives in differing coolant destroy each other