leaking coolant 1998 k1500

I have a problem with my 1998 k1500,4by 4 ext cap 305 motor leaking coolant fluid .happens after I fill resevoir up to level it calls for than it will leak around water pump than only till water level is down in resevoir than no leak any kind for last mouth of driving long as I don't fill resvoir up.temp runs 180-190 has never overheated.and runs like i when i bought it new,truck has 85000 miles on it.have a friend who has a 97 truck same as mine he had new water pump put it his truck 6 mouths ago for same problem still has to run his resevoir down.had him drive my truck .after told me my truck has same smell as his with coolant even after he got new water pump.was told today by a mechanic to buy new water reservoir sometimes theres like a backflow valve and gets stuck open and prevents water from flowing back into reservoir and theres a pressure release valve on water pump that lets xx coolant out.has anyone had this problem thanks in advance

It sounds like the water pump seal is starting to die. I've had that happen on a few trucks. It usually leaks for a week or so and then starts to gush out of the hole in the bottom of the pump. I don't get why it would stop when the overflow bottle is empty though!?

I just bought a new radiator for my truck. As simple as it sounds, the guy at the shop told me that lots of cooling system problems he sees are from old caps that are no longer keeping the proper system pressure. Is it possible that this is why you smell coolant all the time?!? He also said NOT to use the caps with relief levers since they tend to leak pressure and then don't pull enough from the bottle when the engine cools.

Just a thought!

-Derek