2011 Volvo 780 with a d13, Pretty sure losing coolant internally

Initial info leading up to today:
I have 2011 780 with a d13 and 13 speed. 688k on the clock. I've had a slight coolant loss for a few weeks now. Figured it was from one of several places that are hard to see and just hadn't had time to get it pressure tested. No white smoke, no water in the oil or fuel water separator, no other issues other than the occasional regen from idling, so I want really concerned about it.

The problem:
Yesterday when I tried to start the truck after a 34 hour break, the truck was really sluggish to start. Coolant was maybe 1/4 inch below min so I topped that off first, then went to crank up after everything else looked ok. Like I said, it was a bit sluggish, felt like batteries were low. I hooked up the charger, gave it half an hour and tried again, still felt sluggish, so I let it sit for another hour and a half. This time it was still hard to start but did fire up. Ran like **** for maybe 5 seconds and then evened out and idled normally.

A couple hours into my run, I got a fuel filter related code on the dash. Fuel water separator was about half full before I left but almost to the top when I pulled over, so I changed the filters and the light went away.

My personal thoughts:
I figured the two issues were related. Maybe a little water in the fuel was causing the hard start, but the coolant was low again. Didn't look like water in the separator though, so that seemed unlikely. That got me thinking about internal water leaks. Egr cooler shouldn't give me hard cold starts like that, because the coolant would typically go out the stack as steam, but a head gasket leaking between the water jacket and cylinder would due to water in a cylinder. I hate that I didn't think to look and see if there was white smoke when it did crank yesterday, so not sure on that. Still no other issues at the moment. No coolent seems to be anywhere in the other fluids and the levels are where they should be. The only thing I haven't checked is the transmission as far as that's concerned and I doubt that's going to cause a hard start. What do you guys think?

 

Lol sorry about the book. Didn't realize it was that big of a post until I finished. Just wanted all the relevant stuff I could think of on there so I don't have to answer unnecessary questions from the start

 

How's that?

 

Yea I really need to do that but got no idea how to go about it

 

I would have but didn't cross my mind until a few minutes after the fact and by then it was too late. That's definitely on my to do list tho. I've been bouncing the same questions and ideas off a mechanic friend of mine that knows these engines better than I do to get as broad a range of ideas as possible. I'll probably drop by his shop tonight and shut down overnight to try to duplicate the hard start.