Please help! Heat doesnt work!

[shoplizard]

Hi, I have read your story and I feel your problem is a flow through the heater core problem. When you replaced the heater core, what was the condition of the coolant? Was it clear and not cloudy and orange, like rust sludge. I used to see a lot of that in R and W engines. Did you flush the cooling system thoroughly, pulling the drain plugs to flush the block? If the coolant was contaminated with the rusty debris when you replaced the heater core, it could plug again shortly after replacing it. This will cause a restricted coolant flow through the core. You note that the core will be hot with no air flow but with the fan on and low air temps, the limited coolant flow will cool rapidly and produce cool air again. I suggest you back flush the heater core and if the coolant is contaminated flush it thoroughly and replace with new 50/50 mix coolant.

 

[retiredsparky]

^^^^^^^^Bingo! Very common in older vehicles that at one time or another did not have properly scheduled coolant replacement, especially with the "long life" coolant. A gel can build up in the coolant system, or rust or silicates, etc.