Ford: Ford heater core, heater hoses, heatercore

Question
I am quite the handyman, when it comes to cars theres not much I wont do besides a full rebuild and spark plugs on my 2000 taurus with the FFV 3.0 motor,(its not worth the time). anyways I was wondering where abouts the Heatercore is on them, mine blows warm and then cold in the same 2 minutes. I wonder if its plugged, also My check engine light is on I had it checked an they told me it was a vaccume leak somwhere, where there any problem spots on these cars. and if so would this affect MPG, I get about 20 on the Highway
thanks Jason

Answer
jason go to were your heater hoses go into the firewall from the water pump i want you to squze the hose and feel that crunch . which you will . cut the heater hose after you go to your parts store and get a coolant T flush kit . then if you have a air hose handy put it in to the one going into the firewall and you can wash all the crap come out. then install the flush t and hook your garden hose.  up to it  with the car running . and flush away.good luck