My car is leaking coolant constantly but there are no visible leaks. Car is at a HVAC specialist now and they've done all the pressure tests, visible checks and can't find a fix for where the coolant might be going. The car had the pressure test done overnight to see if it would hold pressure to test for the Head gasket but nothing. I was told previously that I had an oil filter adapter gasket leak. Could that be the culprit but I checked the oil dipstick to see if it looked milky or caramel color and it looks like clean oil. Any suggestions???