My 92 Ranger, Sam, doesn't get hot for me anymore. I know her juices still flow, but she's just at that age where things aren't like they used to be. With all that being said, here are the issues. Well, I should say "issue". I didn't have any heat in her at all. I swapped the thermostat because I already had one, and I have some heat now, but it is intermittent. It will get warm while the truck sits and idles, but as soon as I start driving the heat cools off. Does this sound like a heater core issue? Ford heat is notorious for melting you out of the truck pretty quick, but Sam takes forever to put out even the little heat that she does. I'm leaning toward the heater core, but it's not leaking, the windshield isn't fogging up, and I don't smell antifreeze. Of course, those symptoms all point toward a leaking heater core and not one that's just gunked up inside. I would appreciate any and all suggestions. Thanks in advance.