Thanks for your reply.
As a matter of fact, the beginning was bubbles in the reservior and crazy swing of temp gage. And smell of gas in coolant, cold inlet radiator hose and hot outlet radiator hose. So I checked thermostat, it was fine. Then I decide to replace water pump. When I take out the timing belt, I just marked everywhere so that I could just put it on the same marked spots. But somehow when it came off, that camshaft turn spontaneously and off the mark, got stuck. It's 98 Forester EJ25D and only 90,000 miles on it. Crank time mark is off. I'll try to align the crankshaft first and then try the camshaft again.