2001 Tahoe Over heating

Hi, my sons 2001 tahoe is overheating. It runs and was running for a while until it set up for a month and now it seems to over heat. there has been a slow decrease in coolant over time but we never seen a leak. there is flow within the cooling system (water pump working) , there is no visible leaks, the thermostat opens when tested in a pot of water. Everything seems ok. The top hose and bottom hoses both get hot indicating flow.

However it still over heats after a while. I started noticing that I am getting water dripping out of the exhaust. I was able to collect a 1/4 pint glass in 15 minutes.

I have put a pressure tester on the reservoir and it seems to hold but does drop a little over a long time.. eg, its dropped 2 lbs in 20 minutes.

I also did the pressure test with the spark plugs out and it still hangs in there.

in general there seems to be a leak but we cant see where its happening. I have to add a half gallon almost every time the engine cools down.

there isnt any water in the oil. The engine runs ok.

I guess my next test is a compression test but what else can this be?


Thanks in advance

lookup Castech heads - the coolant goes out the exhaust
http://ww2.justanswer.com/uploads/Bluegorilla/2008-12-05_142924_Coolant_loss_5.3.pdf

Have a look at the inside of the oil fill cap?

If adding half a gallon almost every time the engine cools down is considered a slow leak over time, I'd hate to see what a fast leak is. You would expect that the oil would be milky by now. Have you done an oil analysis?

4 ounces is half a cup, so in half an hour you're losing 8oz which is a cup. I'm thinking that's more than normal condensation from the exhaust.

Castec heads, as stated... known failure points...right out the exhaust

You have a cracked head or a blown head gasket. Worst case, you have a cracked block where the coolant is flowing to the exhaust port. There are other ways for coolant to get through to the exhaust, but these are the most common.

Is there a test that I can use to confirm the diagnosis. I dont see water in the oil and the motor was running like normal. Just overheating quickly and losing coolant somewhere.

The coolant pressure test seemed to show the system held up under pressure. The pressure initially set at 15 psi was only down to 14 after 10 minutes. That with the spark plugs out.

thanks in advance.

Chemical check is one way, usually available at auto parts stores.

https://www.2carpros.com/articles/head-gasket-blown-test

I was able to confirm his heads are castech heads with the 706 casting number on the head. I wonder now if its better for me to have a complete rebuild of the motor since its going on 19 years.