I have the 5.3L engine in my 2005 Tahoe. Been having to add coolant (dex-cool) for the last couple of months. I know about the castec heads and pulled one rocker cover and don't have one on that side. (I'm guessing that I don't have one on the other side, but haven't pulled that one yet.)
Changed my oil yesterday and at first, nothing came out of the oil pan. Yeah, it did after I stuck a screwdriver in and moved out some of the sludge, a bunch of sludge. So, I'm assuming I have an internal coolant leak. Since I don't have the castec heads, and can't see any coolant in the top of the heads, it seems that it could only be head gaskets or the intake gasket and I know the intake gasket has caused coolant leaks in these engines.
I think I will pull the intake manifold off, but want to make sure my thinking makes sense and don't want to do all that work if I don't have to. Am I on the right track?
This may give you a place to look before you tear down further
Last year my 1999 gmc 4.8l 250,000 km had all the issues with the valve noisy lifters, loss of coolant with no visible sign of leaks on outside of engine.
I checked to see if I had the castec heads and did not.
Another thing I found in regards determining if you have antifreeze in you oil is your oil will not always be ' milky' on the oil dipstick to confirm that antifreeze has mixed with the oil, antifreeze does not like to mix with oil. You have to drop your oil and if it comes out kind of chunky or blobs, you have antifreeze in the oil, it will end up on the bottom of your drain pan.
I found the problem when I pulled the intake manifold off, THE TOP ROW OF BOLTS ABOVE PUSHROD GALLERIES, (11mm, not the main head bolts) ON THE LEFT HEAD HAD LOST TORQUE and subseqently antifreeze was able enter the oil pan via the valve pushrod galleries, there was evidence of corrosion, etc on the pushrods, aft lifter area.
At this point I was 90% sure I found the leak but decided to change the head gaskets, when they were pulled I found no evidence of leakage around the head gaskets gaskets.
So what I suggest, pull your intake manifold off, (only way to get at the smaller 11mm? bolts) check torque, if loose retorque, put intake back on (new gasket), if not and no sign of corrosion etc in pushrod galleries continue on with changing out head gaskets. If you do this it should take, 2-3 hrs versus 4-8 hr for a head gasket change depending on your experience.
If you are looking for a complicated explanation for this problem there is not one, that was all it is.
I see have seen quite a few of posts looking for a fix for this issue, this is the fix. Unless you think the auto parts industry needs more of your hard earned dollars, check this this out. Let us know what you find, Good luck.