GM-GMC: Big block coolant mystery, c3500, coolant

Question
Harry,
I have a 1996 Chevy C3500 with the 454 big block engine.  I can find no leaks, but the truck continues to empty the coolant reservoir.  I have had the compression tested, and the mechanic said that all cylinders were within tolerance.  Is this an internal leak?

The truck has 120,000 miles.  If it is an internal leak, is it worth fixing the motor?  Or is it time to trade out?  Thanks!  I really appreciate your input.

Answer
You can have the cooling system pressure tested to see if it will hold pressure with the engine off.  If it does not, and there are no external leaks, coolant is leaking internally.

If you have an internal leak, the coolant will eventually cause the engine to seize because cooalnt in the motor oil is very bad for the engine.

Fixing the engine depends on what you do with the truck, what you would spend to replace it, and what the repair cost would be.  Only you can make that determination.