Civic - Honda :: 2001 - Leak In Coolant Reservoir

My 2001 Civic sedan coolant reservoir was full after a long drive - with coolant blown out from the top. I am trying to isolate the problem.

1) I Did not notice if temperature gauge rose above the mid-point on the gauge.

2) I Discovered issue after 120+ drive on a hot day (90 degrees plus).

3) The car has almost 230,000 miles.

4) About 1,500 miles prior to this incident I removed my drive belt and replaced it with the shorter drive belt to circumvent the A/C compressor as it or the compressor clutch crapped out on me.

5) The morning after this occurred the coolant reservoir was still ful.

6) I removed the radiator cap and ran the engine for about 15-20 minutes. During this time I noticed the coolant in the radiator begin to rise into the fill neck area of the radiator - no bubbles or movement other than up into the neck area. The top hose was warm and then got hot but it seemed the bottom hose remained cold. I then throttled the gas briefly and nothing happened to include the radiator remaining off. The temperature gauge read just below the mi-point. I then throttled up to about 3,000 RPMs and coolant blew out of the radiator – about 1/2 to 1 liter of coolant came out. At that point, I shut everything down, installed the radiator cap, and cleaned up the coolant. I noticed the bottom hose appeared to now be much warmer than before the coolant blew out. The next morning the coolant reservoir was empty.

7) Today, about one week later, I applied power at both fans and both worked. I checked the relays and both registered no continuity across terminals 1 and 2 - as they should. I checked the radiator fan switch for continuity when cold and there was NO continuity across the contacts - as it should. I ran the engine for about 20 minutes with the radiator cap installed. The temperature reading rose to just below midpoint (normal) and stayed there. Radiator fan had not come on yet. I throttled up and nothing. Idled for several minutes and the temperature gauge rose to about ¾ of the way to “H.” I throttled the engine to look for smoke from the tailpipe – there was none (there is no history of any kind of smoke coming from the exhaust of my civic). I throttled up again, the temperature gauge dropped quickly below the mid-point, and the radiator fan came on for the first time. After the fan kicked off the temperature gauge again rose to ¾. I hit the gas, the temperature gauge dropped quickly to below mid-point, and then the fan came on again.

I was thinking this could be a blown head gasket but now I am questioning my initial thoughts. As of right now there is no coolant in the reservoir. One would think if the head gasket was blown that I would continue to get fluid in the reservoir even with the lost ~1 liter from my earlier test. I checked my engine oil dipstick and it looks clean - just oil. Nothing unusual visible when oil fill cap removed. Wy my coolant reservoir would have filled, blown over, not empty when cooled, only to empty out by the next morning after blowing 1/2 to 1 liter. This has been a loyal car (other than the recent loss of A/C) and I would like to see if I can get 250,000+ miles out of her with no serious maintenance.