My Caravan has about 55,000 miles on it. Last night, the engine gauge went all the way to hot and the coolant light came on. When we started it up today, my husband put some water in it, and it stayed okay until we had driven about ten miles. Then the light came on again and we heard a warning beep. We also heard knocking in the engine as he accelerated. We filled it up with coolant/antifreeze and let it sit for about 1-1/2 hours. When we got back into the car, it wasn't fully cold (outside temp was 35 degrees), The gauge stayed at about half, which is where it normally does. As we were driving home, the gauge went to hot again, then slowly back down to normal (half), then hot, then normal. It's really puzzling, and we can't figure out what it could be. Could it be the radiator? Also, for last couple of months, it doesn't warm up the way it used to. In other words, we don't get hardly any heat in the car. But tonight, after we put coolant in it, we did get some heat, but only temporarily. Could these two problems be related? Please help! Thank you!