ok so i recently did a b20 swap and now that its getting cold ive been using my heat more often but lately ive been missing coolant i thought maybe head gasket but thats not the case no oil in the antifreeze vice versa its never to the point where i have none left the resivior is just always real low or near empty i dont see any leaks but im not sure whats going on

 

heater core

 

It may still be the hg, it can have a very small leak. I had a similar problem for a few months until it finally got worse. But I would stop using the heater for awhile and see if you have the same problem.

 

I was missing coolant mysteriously, looked under passenger carpet and found a puddle there. My heater core cracked or something