I recently had an oil analysis done after changing my oil before winter.
They found a significant amount of antifreeze backed up by my having to
add some during the last part of the season. It's a 1987 5.7L GMC with
closed cooling and 770 hours. It uses no oil and runs great.

I'm trying to determine the possible causes. I've heard:
1. Cracked block
2. Cracked head
3. Bad head gasket
4. Bad frost plug
5. Bad coolant pump (supposedly located on pop of the engine by the
manifold)

Any other ideas?

Capt. jeff