clogged heater core?

I had intake manifold gasket leaks and was told to use a "stop-leak" type of additive to stop it. It didn't work and eventually I replaced the motor with a new crate 350. This is when my problem started.
When the mechanic removed the heater hoses, the additive set up in the hoses and core and when everything was put back together, NO HEAT!
My question: Is it possible to backflush the hoses/core, with a pressure hose or something, or am I just screwed?
Be gentle with me, I'm new at this.

Welcome to AF. I'll be as gentle as I can. You didn't say what vehicle you have but since you posted in the Sub forum I'll just assume.

Back flushing is something to try.

I would take the hoses all the way off and flush them 1st. Then with the hoses off try and back flush the heater core somehow.

If you have the rear heat & a/c system you may have to do the same there.

I think others may jump in here on the "stop leak" thing.

Good luck and please let us know the outcome.

I had intake manifold gasket leaks and was told to use a "stop-leak" type of additive to stop it. It didn't work and eventually I replaced the motor with a new crate 350. This is when my problem started.
When the mechanic removed the heater hoses, the additive set up in the hoses and core and when everything was put back together, NO HEAT!
My question: Is it possible to backflush the hoses/core, with a pressure hose or something, or am I just screwed?
Be gentle with me, I'm new at this.

i used to use stop leak in the old days this worked for me for many a year. with todays engine manufacturing designs this can be dangerous as the flow path is much smaller now. so my question is what did you use and how much ?

whenever installing a new engine I would buy new radiator. if this is 12years old...........

The vehicle is a 1996 Suburban and the stuff I used I've forgotten the name of but it was on the semi-thick side and had fibers of some kind in it.

I know I'm gonna catch some crap about adding it (like I haven't already) but I was following the advice of a (previously) trusted mechanic.

If I need to flush the rear heater hoses also, where do I find them?

Look for the hoses from engine or rad to heater.
Remove them from heater core and see if you blow threw heater core with air.
If not it is pluged beyond cleaning.
If any air will blow threw it take a water hose and fliush it as much as you can.
Or last resor But be carfull with it.
Because It is strong stuff.
Wear eye protection and shin protection and do not get any on your body or car paint.
Hold up one heater hose and pour a little muriatic acid into it.
Let it sit and then flush out with water.

Also you may have a plugged up rad.
Good Luck
MT

Okay...UPDATE....

I took off both hoses where they go into and out of the heater core and blew air through from both ways.

Antifreeze came out both times.

Now I'm stumped. The top radiator hose is hot when running so that means my thermostat is opening, right?

Also, the temp gauge on the dash is running normal temp.

Someone told me that when the engine was switched out that the mechanic might have failed to hook up a vacuum hose that switches a "door" from heat to cool inside the vehicle.

Make sense to anyone? and if so, where do I look for this legendary, stubborn portal?

We'll lick this thing yet, I can FEEL it!

reed:banghead:

Most of the heater control doors and heater and heater water shut off valve are electrical controlled on yours.
Check all fuses and check water shut off valve for opening and heater hose coolant circulation.
Feel both heater hoses they should be hot or real warm to the touch.
Then check your mode and tempt control doors for opening and working.
MT

While poking around aimlessly waiting for an idea to present itself, I thought to turn on the rear heat ...it works but not REAL hot. Definitely warm, though.

If there is circulation through the front heater core and now circulation through the rear one, have we narrowed it down to this "door" theory?

I have no idea where this door or doors are or the water shut-off valve. I'll check for warmth on the lower radiator hose (top one is very warm), and related fuses.

Keep the ideas comin. They're all appreciated!

While poking around aimlessly waiting for an idea to present itself, I thought to turn on the rear heat ...it works but not REAL hot. Definitely warm, though.

If there is circulation through the front heater core and now circulation through the rear one, have we narrowed it down to this "door" theory?

I have no idea where this door or doors are or the water shut-off valve. I'll check for warmth on the lower radiator hose (top one is very warm), and related fuses.

Keep the ideas comin. They're all appreciated!

i believe that coolant always flows through your heater cores, and it is the vacuum operated door that is stuck or vac line problem, this blends heated air with outside air. on later 99 on up they used electric controls. anyone know for sure? this is 96 model?