there are additives in the coolant that resist corrosion thats why you should never run pure water through your system even if it is distilled

 

Make sure your system is primed. After running til its hot, let cool and pull your temp sending unit (on thermo housing) to make sure its full of coolant. That should be the highest point in your system and all air bubbles should escape from there.

Good luck!

 

is the gasket blocking the hole for the heater core flow ?

 

Go to you tube and type in unclogging a heater core click on the one by eric the car guy this may help you.

 

it was in imperfection in the T stat housing i bought ...the cast has a blocked off passage and i had to re drill it