1988 Lincoln Town Car coolant

Can anyone tell me what a radiator cap extension is used for. I am losing coolant somewhere from my reserve tank. Can't see a leak anywhere. I seriously doubt that my intake gasket is leaking. This car purrs like a kitten. Just picked it up 3 weeks ago. Was basically parked in garage for 10 years, but was started occasionally. I haven't had any dye check yet, but will if needed. Not sure if the coolant loss is just a time thing or associated with driven miles. Seems to go down in the tank about a pint every couple of days or about 100 to 175 miles. Was wondering if the extension first mentioned was a fix for a heigth problem from top of radiator to overflow tank. Like I said, I have a hard time believing that that motor would not run rough using that much coolant. Any help would be appreciated. Thanks, Bill