99 Manifold leak w/antifreeze smell - now have a click when cold - Flat Lifter?

[bumsinflt]

99 Tahoe - 77.0 miles - had slow decrease in antifreeze - noticed overflow tank always empty - slight smell of antifreeze - now hear clicking after truck sets overnight and cold (0 to 20F degrees) sounds like a flat lifter (does this engine have hydraclic lifters?) and goes away after about 5 mile drive - I added a detergent oil for lifters, it reduced noise by 50% but still can hear very faint click after 100 mile drive - I figure I will need to change manifold gaskets (per other threads with similiar anti-freeze problems) - how can I tell what lifter it is and will I be able to fix that lifter at the same time I do the manifold gaskets? Should I do all the lifters since I had problem with one? Is it ok to drive it with a flat lifter? Thanks

[wild bill]

Check the quick connect heater hose fitting for dicoloration at its base and check the front of the intake behind the accessory brackets.Could also be water pump. The tick noise is something GM is aware of as there is a TSB about this exact problem.My 2000 has it too. No loss of power just noisy. GM says it is carbon buildup on top of the pistons so I am going to use some GM top engine cleaner and some SeaFoam too clean them all up. Hope this helps.

[bumsinflt]

Originally Posted by wild bill

Check the quick connect heater hose fitting for dicoloration at its base and check the front of the intake behind the accessory brackets.Could also be water pump. The tick noise is something GM is aware of as there is a TSB about this exact problem.My 2000 has it too. No loss of power just noisy. GM says it is carbon buildup on top of the pistons so I am going to use some GM top engine cleaner and some SeaFoam too clean them all up. Hope this helps.

Thanks for the help!