One of the defects, if I can you this term, of this engine is that it traps sediments and crud in a part of the water jacket. On the left side about half way down you will see a lump in the casting that runs frnot to back. At the front is a little frost plug and at the back on the side is a drain cock for the block. This area always seems to fill up with junk, and in some cases I've seen the block crack along here from freezing up after a person thought the water was drained. To clean out this, area with the motor still in the truck, remove the plug at the front and the cock, then run some high pressure water though this opening. Sometimes this area is full of hard stuff, and you just straighten out a coat hanger and run it in and out to dislodge the stuff. It takes a little time to do this, but its well worth it, as a blocked passage here leads to over heating troubles down the road.
