I have a 2002 Blazer 4.3 4x4 I got up this morning it was -1 degrees F outside started blazer to let warm up, was warm after 10min went to gas station put gas in and drove about 15 miles on interstate and noticed it was blowing cold air and overheating pulled over turned off motor opened hood did see steam and coolant around radiator and I could hear coolant boiling inside system, upper and lower hoses was very soft when squeezed but after I let it cool down it started right up and started blowing warm air, temperature gauge was right at the halfway point and I was able to drive home again about 15 miles the temperature gauge never went over halfway until I pulled off the interstate and it than started blowing cold air again and gauge started rising again. Please any help would be appreciated if you have any questions I will try my best to answer them

 

You should never see steam nor coolant outside the radiator. There is no reason to hear any boiling of the coolant either as when pressurized it would boil at a higher temperature (about 255'F at 15 psi). Would appear you have a serious leak that must be repaired.

From where did you see the seam and coolant originate? Hopefully your leak is from something simple like a hose but even a radiator replacement is a straight-forward fix.

You did not mention the level of coolant in the overflow tank? What level was it at each stage of your driving?

If you must drive around more watch that temperature gauge and make sure your coolant system is filled with 50/50 water coolant!

I'd like to hear what others think but I would surmise that as the system heated up and the leak got worse, you got steam/air into the heater core which would have made it much less effective as a source of heat. When you stopped it and the system cooled a bit, coolant must have been sucked back into the heater core, displacing the air/steam, providing some heat again.

 

I agree with Christine. You've developed a leak somewhere. Could be the water pump, a hose or the radiator core itself. The issue with locating the source is the fan blows coolant all over the place. So check everything closely. If the water pump has failed there is a weep hole just above the pulley on the water pump and would be the first place I would check to see if coolant has come out of there. I suspect the boiling you're hearing is actually an air pocket that the coolant is gurgling past/around. One of the symptons of low coolant is the heater blowing cold air. So definitely check the coolant resovoir with the engine hot. Once you have repaired any leak insure you burp the coolant system by raising the front end of the truck and letting the engine run through a couple cycles of the thermostat opening with the radiator cap off. Top off as needed. This will insure you do not trap an air bubble in the system.

 

Check the strength of your anti freeze - A slushed up radiator can and will steam and blow out the over flow tank blowing coolant across the engine and radiator - Being in Wyoming during our winters here I've seen this a lot of times.

 

Simply not enough anti-freeze and the radiator frozen?