Heater starts blowing cold air when coming to a stop

i blew a head gasket so ibflushed the cooling hearing system and put in a stop leak product. Tah dah! It worked!. I was just wanting a temporary fix until I replace the motor. Yeah, and it was my wife's suggestion. But the hot air turns cool when I slow down or stop for a light. I am hearing some chatter which I think is the timing chain, but couldn't be the water pump? I knew the truck had some issues but the frame body and interior are flawless. that is why ibdont want to pour $$ into the present. I'm allbears! Murf

 

I had that happen with a vehicle I owned many years ago, and the problem was an obstruction in the radiator. Under acceleration when the water pump is spinning faster, it produces more pressure to circulate more coolant, and you'll get more going through your heater core. At idle, the obstruction is too much for the pump to overcome at low speed. That stop leak stuff you put in there could have exacerbated the obstruction. I ended up needing a new radiator.

 

Roman. thanks, I knewn I was , rolling the dice when I decided to put the stop leak in. Darned if you do darned if you don't! I just need a temporary fix until I decide where and who will replace the motor with a new rebuilt and a warranty. The head gasket is a big ticket repair I don't know about the water pump I'll find that out today. I truly appreciate your comments

 

I taught school, exacerbated, kewl word. Took it to a radiator shop and the technician noted the hose from the block has been slit back to the return. Go figure, he showed me what to do so tomorrow well see.