I bought a used 93 3.1 GM long block engine with 19,633 miles in 2014 from a yard that I found on the internet. The engine was pulled in 1996 and stored by the yard. I did a title search/check to verify this. The engine was installed in 2014 in my 93 Grand Prix to replace the 3.4 and after the install I have a clogged heater core that I didn't have before. After being pulled the engine sat for 17 years. So my question is would anti-freeze leave behind a residue that would have caused this? And if not could you give me your thoughts on this situation? I flushed and reverse flushed the heater core seven times. That Heater Core was only 5 years old. Thanks
My suspicions would lean more towards debris left in the block. Most salvage yards by their nature are not particularly clean. My thoughts would a rodent nest or other debris. Another possibility is not a clog but an air pocket that has settled in the heater core. If you check this site for no heat links you may find some info on determining how to resolve this.