This is a 3044C engine right? Serial number would help. Its decessor, the C3.4 did have some head gasket issues. The 3044C might have also, but I wasn't working on Cat machines then.
If it is coolant you will be loosing it. You won't pick this up unless you check the level stone cold (say the following morning).
As for the rain water theory, the valve covers on these do crack often due to overtightening, but you'd have an oil leak if that was the case.
Yes 3044C. I dont have the engine serial number but the machine is CYC01477
I don't see any cracks in the valve cover, nor oil leaks.
When I replaced the head gasket, just about a month and a half ago, I filled the coolant system and then the overflow bottle/expansion tank to just below the full line. I see know that the level is at the low line. But I have only run it once for 20 minutes since the new headgasket and fill up, so that couldve been the air escaping the system from fillling it up from empty. I also dont think I filled the radiator all the way to the cap, but when I took the cap off today, it was full to the cap, overflowed a little, so that wouldve taken some fluid from the bottle as well.
Also, the system is still holding 16 psi for going on 2 hours now