OK guys, this is bizarre.
Good news is that I had leakdown and compression tests on all cylinders and it all came out good, no indication of head gasket breach or cracked head. Still not seeing any other signs whatsoever that coolant is leaking into the heads.
Mechanic pulled out entire cooling system, advised that he believed that it had been leaking at one place near the block and near the heater core (apparently not picked up by the pressure test). He reassembled the system, flush/cleaned out everything, and replaced the coolant.
I did expect to continue to see some air pockets, and over the next few days found myself topping it off a few inches on the radiator but about the same amount each day (i.e. not improving). I could also hear some air pockets in the dash when I ran the heater. So I figured I just have some air in the system (not a surprise, because I know he gave the heater core a good cleaning). I figured it needed to be burped.
First parked it on an incline with the radiator fill at highest point, but got quite a bit of splash out at operating temp and revving at 2500 RPM. So the next day, I took a 2 litre plastic bottle and cut the bottom off. I took some electrical tape and wrapped the spout so I could get a reasonably good seal around the radiator intake and filled it with 50/50, it was fine. I started the car at idle and it burped out into my funnel and I added some water, keeping it about half full. Eventually the bubbles stopped and it started to simply suck the water down and discharge out through the expansion tank cap outlet. I figured at that point it was successfully burped. Also, to my pleasure, I noted that while it was running it did not seem to be generating air...once the air in the system was purged, the bubbling stopped. That was last night.
This morning after about a 10-15 mile drive and a 1.5 hour cooldown it was down again a few inches in the radiator. I didn’t have water with me and had to make another stop, so I drove it for about 10 minutes and made my stop (about 15 minutes). It was still hot but I needed to get on the road, so I covered it with a towel and slowly released the radiator pressure from the cap. It was still low. I left the cap off and went to hunt down some water (5-10 mins)….when I returned, the level at the radiator had recovered (I assume from the recovery tank). So, I have no idea where the air is coming from at this point.
Any suggestions of what to try next????
Thank you
Jeff