When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
HAve you tried looking at the heater core? Can you smell any antifreeze? I would suggest pulling your heater core and looking for any sign of leaks. If you see any discoloration on the core itself, change it.
a few other things too:
there is a heater control valave for the hot coolant flow to the heater core..near firefall on pass side of engine compartment..it may be stuck.
next is heater control rod mech. to that valve
plugged core from minerals, etc.
water pump gong bad...is temp rising more than normal?