I installed the Hondata gasket on Monday. Things went fairly smoothly for the most part. During the install, I lost probably 1/2-1 liter of coolant during the process. And I finished, I of course added coolant/water mix into the overflow back up to the max line. I started the car, let it run a few minutes, and then rechecked the level. It was still at max. I took it for a 10 minute test drive, and rechecked the coolant upon my return. Still at max.

The next morning, the coolant level had gone down to about halfway between the min & max lines. I figured there was some air in the system before, and now that the air was out, more coolant was pulled into the system. As such, I filled it back up to max. I rechecked the level when I got to work, and when I returned home from work Tuesday. Both levels were good, at max. I didn't have any overheating issues or anything.

When I checked it Wednesday morning, the line was down near the min. WOW. So, I add more coolant, thinking either I have a small leak (intake manifold bolts need retorquing?) or there was more air purged. Either way, I add and drive to work. I check at work and upon my return home from work. Both levels good, at max.

Now today. I checked the level this morning. It was perfect. Right at max. Ok, so I finally got rid of the air...WRONG.
On my drive home today, the car overheated. About 3 miles into my trip home, the temp gauge was all the way full in the red. As soon as I saw it, I pulled over and popped the hood. The coolant in the overflow was about 1.5 inches about the max line. WTF? Baffled, I use the tube in the top of the overflow cap as a "pipet" to take some of the coolant out, down to the max line. This takes about 10 minutes. After that, I restarted the car and the temp was perfect - 3 bars. Hmm. I drove home with no problems, and the coolant is at max now.

I'm baffled on this one. More air in the system? It's too dark to work on it now, but what should I do in the morning? Air purge valve?
Thanks in advance.

 

Sounds like air in the system. Did you have the key on and the heater all the way to hot when you where filling the system?

 

If you got air into the system, to bleed it properly requires you to idle the car with the heater control knob to HOT. This opens the heater core to the rest of the cooling system. Then you start at the bleeder valve beside the throttle body. Open it till coolant comes out. Next you go to the bleeder on the metal line high up on the firewall. Open it till coolant comes out. The level in the reservoir will go up when the engine warms up and only draw back into the system (go down) as the engine cools. You don't have to worry about the level being over the max line until things stabilize. Anything above that level won't hurt anything and will only puke out if too full - not a big deal (except environmentally speaking).
Of course, it is possible and likely that your gasket job left a bad seal and the cooling system is not holding pressure continuously. This will cause an overheat. Do you notice any steam from the engine bay when it's running hot? Like as if coolant was leaking from the new gasket area?
Also, have you checked to see that your rad fan(s) are cycling on? Maybe something happened during your mod and you did something to the connectors and forgot about it? Then check to make sure that the water pump is working. This will be difficult. You can best check it by starting the car when cold with the rad cap off. As soon as the thermostat opens, you'll see coolant flow if the pump is working. The problem is that you'll lose a bunch of coolant as expansion takes place, so you'll need to suck some out using a turkey baster and collecting it in a clean container so you put it back later. Once you've finished this test, put the cap back on and shut the car off and don't drive it till everything has cooled down. Keep the reservoir topped up during the cool down as it will draw fluid back in that you sucked out.

 

I bled the system this morning before my drive to work. Everything appears ok for now.

Thanks for the input guys!