Overheated on track - now what?

[infernosg]

After the first "event" I filled up the radiator and managed to drive 2.5 hours home averaging 70 mi/hr with no overheating, but the buzzer would come on occasionally during tighter turns and lower speed driving. Once I got home and the car cooled off I topped off the radiator and bled the system the best I could. At this point the radiator was completely full and the overflow bottle was at the full level as well. I was able to drive to and from work (only 8 miles) with no issues on Monday and I let the car sit most of the day yesterday. Yesterday afternoon, after driving more recklessly than I'd like on the street, I came home and revved the engine in neutral in the driveway. No buzzer while doing all this so I turned it off and let it sit for about 30 minutes. Before starting it up again I noticed the overflow bottle was now ~1" above the "full" mark. I made it to the end of the driveway when the buzzer came on. Since it was still fully warmed up I just pulled back up and turned it off for good. The buzzer did go off as soon as I started to move back up the driveway.

What has me most worried is the constant bubbling I'm getting in the overflow bottle. To ensure it wasn't be caused by engine vibrations I removed the overflow cap and tube and placed it in a cup of clear water. With the car fully warmed up there was a constant stream of tiny bubbles coming out of the pickup tube. Only once did a moderately large amount of coolant get burped into the cup. After that it was back to the bubbles.

Pressure testing is my next step before throwing new parts at it (rad. cap, thermostat, water pump). The plan is to swing by an auto parts store after work to see if they have anything I can rent.

The one thing I can't seem to explain is the original overheating event. IIRC, the cooling system holds like 2 gallons of water and I know I didn't add nearly that much after it overheated. The fact the buzzer came on just as the temperature gauge started to rise also has me stumped considering it has come on many times since that and the temperature gauge hasn't moved.

Originally Posted by RETed

I'm trying to be optimistic at this point.

I am a self proclaimed pessimist and worry constantly, but I'm trying!