run the engine, until warm. turn on the heater. check the valve to be sure it opens. feel the hoses, both in and out of the firewall. a clogged heater core will be cold, but so will a core with a valve that doesn't open. you can get a garden hose repair kit, and use the male barbed fitting to plug into the heater hose. disconnect the other end, and turn on the water, and see if it flows. swap the fitting onto the other side, and do it again. you'll see if crap comes out, if it's getting clogged, or nothing will come out, if it's plugged.


this is the fitting, i used.