Help with coolant mystery

[2000tahoeZ71]

I have about reach the breaking point trying to figure out where my coolant is going. I have replaced intake gaskets, water pump, upper/lower hoses, radiator, radiator cap, intake fitting, all heater hoses, and heater core. It's not going in my oil. No obvious external leaks. No coolant smell after its hot. Getting a little bit of condensation on startup, but doesn't smell like coolant at all. Pressure checked it hot and cold, builds and holds pressure. All spark plugs look normal. I can fill reservoir and after a couple hundred miles it will be gone and radiator down to where I can see the top of the fins. The only thing I haven't changed is the overflow hose and reservoir, but like I said I'm not smelling anything from the engine bay or seeing any leaks at all. Any ideas?

 

[chevync]

Do a search on Castech heads, I had the same problem. Castech heads were a bad bach of heads from GM, I had the same problem with mine, I had to replace both heads, both were cracked. Look for the casting number 706.

 

[OR VietVet]

X2^^^^^^

 

[2000tahoeZ71]

Everything I have found is on 99 up 4.8/5.3 motors. I have a 2000 OBS z71 with a 5.7.

 

[dapope125]

Everything I have found is on 99 up 4.8/5.3 motors. I have a 2000 OBS z71 with a 5.7.

I have the same problem here with my 2000 Denali OBS.
Let me know if you figure this out!

 

[OR VietVet]

I would take it to a garage that has an emissions sniffer machine that goes up the exhaust pipe during drivability engine work. You have engine running from cold to warm with rad cap off and they can use the sniffer to check for hydro carbons at the rad neck. That will tell you if the head gaskets are leaking. If is slow enough you may never see the coolant and engine oil mix that would happen in a very bad leak. You still could have head problems but would need to have machine shop pressure test them.