That engine was prone to clogging the heater core from oil getting in the cooling system or the coolant (dex-cool) sludging up from either mixing with regular ethylene-glycol coolant or neglect.
Check the overflow tank (engine cool) for a brown or black sludge in the tank.
Secondly, make sure that you are opening the bleeder valves when you are adding coolant or air pockets will form and the heater will not work.
Finally, pull the hoses off the heater core and put a garden hose on one of the heater nipples. Turn on the hose and watch for water to come out the other nipple.
If no water comes out the other nipple after about 15 seconds it will be necessary to replace the core.
Tuesday, September 16th, 2008 AT 12:14 PM