I have a 2005 saab 9-5 linear wagon with a 2.3 ecopower. The story starts in the dead of winter with a cracked radiator that caused the engine to overheat one time to the point I heard knocking coming from engine. So replaced radiator then a few days later upper radiator hose popped but the hose was in rough shape to begin with. Replaced hose then a few days later the heater hose coming out of the head to bypass valve popped. I realized then the engine was building up pressure and I figured it was a head gasket. But I still had to drive car daily. So I keep the radiator cap barely on so it won't build up pressure and fill it up as needed with water only. Lately I've noticed a rust color coming around fill tank and can see it when I fill it up. I ran a compression test and got 120lbs on cylinder one and got a little over 100lbs on the others. I also have radiator fan on constantly. I've been driving like this for six months and car never overheats and runs fine. So my question is where could the rust be coming from and do I have a blown head gasket? Or do I have a bad water pump or stopped up bypass valve? Also I pulled out the thermostat early on when the last hose popped. Please any advice would be greatly appreciated.