had same problem with my 01 Burban! Nothing noticed during driving for about a year. even no white exhausts.... no water in oil,... - so nothing to worry besides that little water loss. Checked it regulary, so no prob I thought... found on each oil change some muddy yellow-white stuff. Looked like a typical sign for a short distance vehicle as it is... so didn't worry about that either.
Just one crazy thing happened during that time: my oil dip stick blocked. Couldnt get it pulled. finaly it broke.
It broke just at that point where it was riveted. It was sized up in the tull!
Last week I wanted to replace that dip stick and tull. So I took the oil pan of and fixed my problem. Everything looked perfect - nothing to worry: Clean oil, clean pan,...
I let the burban on the auto lift for that night without oil and pan... next day I finished my work.
First try to run the engine: rattling from the engine. Ok, thought all oil left the engine during the night so probably it just has to dispenses in the engine. Suddenly warning "Low Oilpressure". Shut the engine off and waited a few moments. Then I tried again: still rattling and a low oil pressure but no warning. At 1500rpm I had oil pressure at 40 and rattling stopped. Even in idle it was ok then. Just oil pressure was not around 40 as usual, it was at >20 in idle! Started to drive carefully and pressure kept at 40.
Even a day later same pressure. Tried to drive 50-60mph but oil pressure didnt get higher and it started to rattle again. Driving slow was still ok at 40 pressure.
Took a closer look today: almost no coolant left!!!
Put the oil pan off again and found all full of white-yellow mud in there. All the oil was full with coolant!
Discomposed the first head and again
Two cylinders had some water in it! Besides the aspected damaged head gasket I found something strange: nearly all water conduits of that gasket were totaly plugged - just two were free!!!
Checked the valaves with help of gassoline: two of them are damaged. Looks like the valve seating is broken, burned or whatever.... two valves even look like they got damned hot once!!!
Tomorrow I will put off the other head and take a look whats up over there.
Guess it's time for pulling the engine to get it repaired.