I have been slowly losing coolant for a year and a half .Thanks to Talltoms tips I eliminated the timing cover gasket and discovered the red o-ring to the split pipe coming out the top of the water pump failed.I replaced it.Fine for about a week then slowly problem returned.this time I replaced the o-ring,RTVed it.That lasted 2 weeks then started leaking again.Next I tried Hylomar and a new o-ring.It worked..........not.I o-ring and RTVed again to get through the cold months and throw in a gallon of prestone a month.The water pump works perfectly.The split pipe has no cracks.Unless there is a hairliner in the pump where the split pipe enters I'm out of ideas.The leak source is right at the junction of these 2 parts.Anyone else come across this problem.Also where do I find the vacuum that controls floor circulation(I have none)?Thanks in advance.....Pete

 

You probably know about these, but have replaced the lower intake manifold gaskets (assuming your truck is a 97) with the updated versions? Is it leaving a puddle on the ground, or is it a misterious leak?

I replaced the water pump twice on my old 97 thinking that was the culprit.