I have noticed that my overflow jug has been needing to be refilled every couple of weeks. The engine has maybe 5k on it since being rebuilt. Both the block deck and heads were resurfaced prior to assembly. When I put it together I used felpro 1010 head gaskets as these were the recomended ones to use with aluminum heads. I am slowly finding that there have been issues with this gasket.
I haven't found any external leaks or puddles or anything but the coolant is going somewhere. I have pulled the plugs and the appear to be normal. I am running Dexcool, the orange stuff so maybe it is harder to detect on the plugs. My oil seems to be normal as well, it is not all milky or anything. I have noticed that on my first startup of the day I get a real sweet smell from the exhaust.
I am running turbos so my setup doesn't have a traditional PCV system. I am running a Moroso catch can up front. It does seem to fill up rather fast, at least in my opinion. The blow by "juice" also has a very distinct smell much like the exhaust on the first startup. As much as I am going to hate doing it, I think the heads need to come off. Does anybody have any other ideas?

 

I would buy or rent a cooling system pressure tester (Connects where your radiator cap goes) and pressurize it, let it sit and see if you lose pressure. The sweet smell dosent sound good, though...

 

When I had that problem it was simply a leaky heater core. If your heater core leaks, your carpet on the passenger side floor in the very bottom will be wet, and you'll probably smell coolant in the car. A heater core is only about $50 and takes about an hour to replace.

Maybe a possible solution...

 

It isn't a heater core as mine is disconnected. I like your train of thought though, easy stuff first.