lack of heat

[WONDERDOG]

I have a 1996 Mark-8, the blower is working OK but the air is only warm even if I set the stat on 90. The cooling system is OK, the temp. gage is in the normal range but only warm air. I pulled the lower hose off the heater core with engine running at normal temp. - the water is hot, but not much flow. Could the heater core be restricted, the cooling system is clean, I allways replaced the coolant when scheduled. Any suggestions?

[ekooke]

Almost certainly the heater blend door. See: http://www.markviii.org/LOD2/technical.htm

[Tman70]

Welcome, Wonderdog! Sorry your lack of sufficient heat had to bring you here, but I hope the information provided will help to solve your problem.
The Ford/Linc/Merc Shop manual test for heater core restriction is just what you performed when you disconnected the heater outlet hose with the engine running. Insufficient flow is an indication of core restriction. Because of the design and positioning of the core, the transverse tank winds up on the bottom of the core and is susceptable to filling with particles each heatup/cooldown cycle of the engine. I would first suggest removing both core hoses, emptying the core as much as possible using compressed air and refilling with a mixture of water and CLR (Calcium, Lime and Rust remover). Let this sit about 1/2 hour and then try a power flush of the core to see if you can regain any flow. Do it in both directions. If this doesn't help, you are probably looking at replacing the heater core.