talking about heat in your stang,yesterday i spent like 4 hours installing a remote heater core with the built in fan,got it from a stepvan that iam also restoring,stepvan parts store sell them they are quite pricey around 400,,well i located it in front of the passenger seat bypassed the factory core,had to hook it up with that remote skinny heater hose,that hooks up with a t-fitting,it goes to the back of the block,think it goes in the throttle body??,where does that line go to?? well anyways talk about heat,its instant Cancun,Iam ready for the cold,I will return in to the stock core in the spring,,i might relocate it to the back hatch area,,its a 89 2.3 hatchback,,,,some conversion vans have these setups in the rear area,but they have a bit smaller core to them,,,,,those stock cores plug up very easy,and they are not fun to change.mine was just not putting out enough heat,,,,,i ran the hoses through the floor,,maybe searching the local junkyard you might be able to find one cheap,this is my trusty winter beater,have four stangs in total,,i think i have the hottest hottest stang in town
oh by the way when i first installed it ,the hoses wouldn't get hot,had to rev it abit to fill up the heatorcore also disconnected one hose a bit to air bleed it,,...check both of your hoses they should both feel hot,,might be the thermo also,i think your stock core is plugging up,,good luck