2001 Burb LT. Since it started cooling down up here recently I've been smelling a slight but noticeable and constant coolant smell after engine has been running a few minutes, throughout use and after engine has been turned off. This happens whether I have fan running or not, and it's more noticeable when thermo is turned to 70 degrees or more. I have actually smelt a slight coolant smell since purchase but it is more noticeable in cooler weather now. And it seems the more I run the heater the less it smells but when I turn fans down low or off it smells more. Maybe I'm just going insane. IDK No leaks from radiator, levels remain the same since purchase and pressure checked at radiator cap and overfill cap. Overfill tank at normal levels. Lines going in and out of radiator are old but no visible leaks. Hoses running to heater core are both warm/hot when heater is running, no leaks seen or felt on passenger or drivers side floors. Heat did go cold once when I was testing heater core by running heater and fans in late July but when I took it to my mechanic later that day I could not get the heater to blow cold again or since. Mechanic could barely smell coolant and thought maybe heater core leak but pressure checked out and no sign of leaking on floors. Thinking owner before had heater core or other coolant issues he fixed and maybe leaks caused it to pool somewhere leaving it coated somewhere so that I smell coolant now. Thermo isn't opening and closing properly. I just don't know. I have removed and replaced two heater cores in my life and they were both horrible experiences so I'm hoping to avoid that. Is there a second heater core for the rear/cargo area? Any help appreciated.