I did a little searching and found similar threads but not something that fit my problem exactly. Here's what I got.

I flushed my radiator on Friday using the drain plug only (no engine block plugs). I filled the radiator and reservoir up with 50/50 mix and drove a few trips that day with no signs of trouble.

On Saturday I drove 40 hwy miles and then shut it off. I returned to the truck and had coolant running from the vehicle. Upon inspection in the eng bay I had spray everywhere (so I couldn't determine the source) and no fluid in the reservoir. I filled the reservoir back up and continued with no problems with temp although there was a small gurgling noise occasionally.

From Monday until Wednesday I'm now getting temp fluctuations from 200-230 (180 stat installed) with gurgling noises as the eng temp drops down and the heater starts to work. I am still slowly using fluid as well.

I plan on trying to let the radiator burp out any air that might be in the system and let it warm up while I watch for any leaks/sprays. My best guess right now is that it is coming from the thermostat housing but I can't be for sure. Could the flush have caused the stat to start acting up or cause a stat gasket failure?

I do believe that it is coming from the above and not from below. Any ideas?

 

the temperature swings and gurgling sound are caused by air in the system. you can remove it by letting the truck idle for an extended period with the cap off the radiator. some suggest parking it in an uphill position to get the radiator higher than the heater core (that's where your bubble is).

the flush shouldn't have hurt anything. did you remove any hoses - i'd guess you just have a loose hose clamp...

after the extended idle, fill radiator and overflow and reinstall cap and let it sit and idle some more. if it burps any more air, it will suck in coolant from the overflow, and reduce the level in there. the gurgling should stop in a day or two.

the most important thing is to get the temperature swings to stop. overheating is a killer.

edit - if you have something loose, it not only blows out coolant, but also sucks in air - so as long as its leaking, it will always have air in the system......

 

also make sure the rad cap is installed correctly.

 

Most people dont have this tool in their tool box but maybe you can find a loner from oreily's

http://eriksmartt.com/blog/index.php?s=wrx

 

You'll need a pressure tester and apply pressure to the cooling system, let it stay under pressure for a while. 1997 thru 1999 5.2 / 5.9 engine have had a problem with t-stat housing and freeze plugs leaking. The freeze plug thats leaks most of the time is beteen the engine block and bell housing.

 

If you still have the stock hose clamps that came on the truck, that might be your problem too. Those are notorious for leaking. mainly on the lower hose and the thermostat hose.

 

Okay I made sure that there was no air in the system and I'm not having temp swing issues anymore (at least not today, Thursday). I've still got a leak and I'm not for sure if it is the hose going to the stat or the stat gasket area. I guess I'll find out this evening.