I am absolutely dumbfounded with this one folks!!!
I have had my S since new and never had any coolant issues. I have 54,000 mi on the clock so not too high, but here is my situation...

I purchased a M&M Honda Standard (OEM radiator)radiator cap (1.3 bar psi) from Autobacs the other day. I noticed that it would leak, and residual coolant would be sitting on and around the Radiator spout. I noticed the coolant level in my reservoir rose a 1/2" above the max line too. The car has been right at the MAX line since new with no fluctuation. I assumed air was getting into the system. In consequence, I put the stock radiator cap back on. The coolant level rose to pretty much overflowing in the reservoir a much warmer day later, right before I was going to drive a ways away. I bled the coolant several times according to Billman... Billman's coolant bleed

Still, the radiator is always full, the coolant tank has settled to 3/4" from overflowing and then went to 1/2" from the top again where it currently sits after several bleeds. My heater is super bitchin' hot and temp gauge is normal. My fans turn on if I am a high above idle at a stand still. It is still rather cold outside so no fans when just sitting at idle. What do you think is going on here? A new leak in the system allowing air to get in? There are no leaks anywhere. The only change I have made is type of oil. Gulf VTEC Tri-synthetic 5W30 with polyalphaolefin. Oil level hasn't fluctuated either.

Head Gasket...venting combustion pressure into coolant? possible but I hope not

Radiator...clog maybe (lower radiator hose is much cooler than the top hose) Top of radiator itself warm-hot and lower part is barely warm.

Reason I am worried is, I want to drive to the track this weekend and do some laps (about 1.5 hrs away) Towing to track days is not an option for me anymore because I am living in Japan. I have to pretty much make sure the car is going to fly code 1 (no issues) every time out. I don't speak much Japanese so I am avoiding a break down like the plague.

 

If your heat is "bitchin hot" then air is not your problem, and I hope when you did the radiator job you did not induce some other issue.

Pressure test it cold. monitor it for a while in a clean spot in the driveway.

They make a store bought product that can test for combustion pressure building in the coolant system.

Radiator should be completely full in the morning ice cold.

 

Thanks for the reply Billman.

I didn't actually change anything except for the radiator cap. The new cap was a 1.3 vs stock 1.1. Once I noticed that the new cap was leaking, I put the stock cap back on.

I will see about doing the pressure test. I haven't noticed any puddles in the driveway and I have been checking each time I pull out.