NON-CIRCULATING RADIATOR blowing cold air

I was driving my 1991 Subaru Legacy down the road with the heater on and it seemed to be working good, then all of a sudden we felt a cold draft and looked up at the temperature gauge and it was showing extremely hot. It was blowing out the overflow tube and steaming off the engine. The water in the overflow tank was cold. Towed the car back home and installed new thermostat, refilled radiator with water and temperature gauge reads ok while idling, and heater blows warm air. Take it for a drive temperature gauge goes to hot and the heater blows cold air. I have filled this up several times to try to get the air out, but it still does it. Pulled the return line from the heater core, there was no water. Water pump is only 6 months old and appears to be turning. Checked plugs for possible cracked head gasket but plugs appear fine. No steam out the tail pipe and the car runs good otherwise. It has idled for over an hour and half trying to get the air out and blows warm air through vents, but as soon as we drive it, it shows overheating and blows cold air. The water in the over flow tank is always cold to touch.
Does anyone have any ideas of what could possibly be the problem?

Have you thought of it being the head gasket?

Pull the spark plugs, check them for signs of moisture, watch the exhaust emissions for signs of excessive vapor, check the oil for milkiness (signs of coolant), any signs of oil in the coolant?

I have a 92 Legacy and this very thing happened to me. At idle everything was fine. Drive it for about 8 miles and temp. would go sky high. Had the headgasket replaced and everthing has been fine for the last 4 years. P.S. It never did show water in the oil.

Yes i pulled the plugs and no moisture on themwith no corrosion on them. No oil residue in the water and no water residue in the oil. I thought that it was a head gasket also ,but would it run normal without missing ??? I pulled the top off the plug wires while running and they all had good arc so how else could i tell which head gasket might be bad??. The weather is 20 deg. here so i get normal steam out the tailpipe but nothing extreme even after i drive it and get back home after it shows hot.

I too would be very suspect of a head gasket. You can have the combustion gases get into the water jacket (combustion-->coolant) without any other signs (oil-->coolant, coolant-->oil, coolant--->combustion, etc.). You need to have the coolant tested for combustion gases!!!

I'd also hold out hope that it isn't the HG. To purge the system of air, you'll need to raise the front of the car a bit (I'd use ramps). On the passenger top of the radiator, there should be a plug (generally square with a cutout for a screwdriver); remove it. Top up as well as possible. Start car, top up as necessary. When you feel it is full, stop car, replace plug and radiator cap. Make sure overflow tank has sufficient coolant, too so that air is not drawn back into system.

The instantaneous change of the system is a bad sign. I hope it isn't the HG. If you replace one, you should do both. Let us know the outcome.

Nick

I think I have a blown head gasket on the passenger side.

I will start on it this weekend and post updates here-> http://forums.nasioc.com/forums/showthread.php?p=11781237#post11781237

i would try backflushing the system 2 see what the problem is

when you replaced the temp gage did you cut the little dangle thing off and throw it away. You need the pin hole in the thermostat to let the air . I started doing this a few years ago on my legacys and I dont have the air binding that I had for years . I use to drive them a mile and heat them up and then let them sit. they would idle all day and not overheat but drive them half a mile and they would be overheated. I d have to do this 5 to 6 times to get the air out
Drill a small hole or cut the little thingey off. good luck. If it a head gasket try a compression check.