Coolant leak

I have a 1999 Suburban that kept losong coolant. I found that one of the gaskets between the waterpump and the block was leaking. However you say there are NO signs of leakage. Get yourself a radiator pressure tester and pressurize the cooling system for about fifteen minutes to see if it loses pressure. If it does, and there are still no signs of leakage a good possibility is that you may have a small head gasket leak into a cylinder. One way to check that is to do a compression test on each cylinder. Good luck, I hope this info helps you.

I have the exact same vehicle and had the exact same problem. Mine turned out to be a slow leak on the water pump gasket, doesn't sound like your problem though. I would look to make sure you dont have either a front or rear heater core leak or line leak. It sounds like you did a thorough underhood inspection, so if all these items prove ok, then look to the engine itself or tranny cooler, smell the exhaust for coolant and let the engine set overnight and change the oil to check for streaks of coolant in the oil or white goopy creap under the oil cap, both would indicate an internal leak. next, run it for awhile and check for coolant in the tranny fluid or vice versa, which is very serious because coolant eats clutches. any more questions let me know i know these vehicles inside and out.

check the gm tsbs they were aware of this problem and did it seems a hidden tsb they are fully aware of the problem look at your stamp on the heads and see what it says write it down look up the tsb i cant remember what the stamp on the head said but thats the probvlem its a small crack just enough to loose fluid and evaporate in the engine thats why your not seeing anything again research the past tebs youll find it no garages want to touch it i know i have the same problem on a 2002 suburban 5.3l flex and evry garage i talked to says they are unaware of it bunch of hidden bull

I have that same problem on my 1999 suburban 5.7. I found it to be the little rubber cap on a misc. port right under my filler neck on the radiator. I don't know what this single capped port was/is used for but the cap can't deal with the pressures and heat in the radiator. I could never find any leaks until I pushed this rubber cap while my engine was warm and running at idle then I saw coolant drip out. I now have to change this cap about every 6 months to a year. Does anyone know what this port is used for? thanks

depending on miles? its either a head gasket or its heater core leaking into vehicle. do you have the rear heat and air?

I have the same issue. I welded a cap on mine. Radiator shops will do it. It's not used for anything unless you have some aux equipment that might need it.

We have the same issue with our 1999 Suburban XL... we put in a new engine since we loved the SUV. Now we are losing water daily so much that we have to put water in before and after driving it. WE also replaced the water pump a few weeks ago. Sussie Sutton