is it possible to have a overheating problem because of a bad heater core?

 

No. What are the symptoms of your problem?

At speed? At idle? In traffic? All the time? real fast? slow build up?

 

it just slowly starts building up. takes about 5-8 min of driving to get on H. then if i come to a complete stop it starts to cool down a little bit.

 

Check your lower coolant hose to ensure it has a spring and is not getting sucked closed from pressure.

 

The most usual cause (IME) of overheating at speed is blockage in the system preventing circulation. Things like pushing coolant out heater core hoses and other places looking for the easiest escape route cause by the pressure built up from the blockage are common.

What lb cap are you running?

 

Unless your heater core leaks and now there is less water in the system. If not then no.

 

u can buy those plugs that u basically splice one of coolent hoses that go to the heater core and put in a valve. then hook up a a garden hose, open up the radiator and turn the water on. if u have ne blockage that usually should blow crap out

 

http://www.partsamerica.com/ProductD...rtnumber=AFKIT


best $5 I've ever spent

 

A-HA! thats the one +1

 

hmmm.
i guess we're talking the big radiator in the front for engine, not the small for the inside heating.

if the heater is blocked with dirt or rust or anything then water can't circlulate in there to cool down-> sure to over heat.
You mention it already happens after 5 minutes. I'm not too experienced on Mustang engines, but on every other car you have a teperatur switch (thermostate) which is located on the block where the hose goes to the radiator.

The use of this thermostate is as simple as that.
When the car is cold it stays closed. So the water circulates only in the engine. (small circuit). This brings the engine quicker to normal 'work' temperature.
As soon as it's warm enough in the engine, the thermostat opens and the water flows through the radiator (this is when the hose from block to radiator should start getting warm).
If your engine is hot and the hose is still coldish then I'd say that's the problem (thermostat doesn't open anymore).
If the engine is hot and all hoses going to radiator are very hot then the problem might be a blocked radiator).

the following link might not be the one for your engine, but this is what it looks like:
http://store.cal-mustang.com/cm_able...19&CM_SA=0

any opinions on this ?

yah i know. being native german it's not too easy to describe all this :-(

Kalli