I wouldn't rely on the max line in the expansion tank. Remove the radiator cap when it's cooled off (at least 30 mins) and if it's not filled to the top you still have air bubbles. I've been adding water/coolant at the radiator cap for months, though less lately since I mostly take short trips (5 miles or less).

 

Yeah, a lot of people don't understand that it's just an overflow. That's why I like expansion tank type systems, a lot easier to monitor (and safer if you need to open when hot). Every time I open the radiator cap, it's been full. I'll check today.

That's the tough part with this car, I don't daily drive it or anything. It's a car I'm preparing for sale, and I mostly only drive it on shorter trips. Obviously I try to drive it as much as possible though, since I don't want to sell it until I know for certain that this issue has been sorted out.

 

Aaaaand this case has finally come to a close! I began tear down to replace a leaking valve cover on the driver side, and in that process I decided to stick a borescope into the lower intake manifold to check for injector leakage. In that process, I peeked into the open intake valves on cylinder 3, and lo and behind, there is some coolant right on the head gasket! Maybe it needed time for the UV dye to circulate and make the leak a little more clear, because I hadn't seen it before and I checked several times on each cylinder.
Not the ideal outcome, but I'm happy to have found solid evidence that this IS in fact a head gasket leak, and that I'm not just crazy and chasing a non-existent external coolant leak.

Thanks everybody who has chimed in to offer help, and best of luck to others who are chasing these issues! Now to decide whether to sell it as is or part it out... because I'm too deep into this car to fix it.

 

Sorry to hear that. I would highly recommend a rebuild if you have the resources but known running engines are getting pretty cheap these days.

 

Yeah, that’s the hard part for me. I bought this car as a flip last April, and I STILL have it after all this time. The last thing I want to do at this point is a major engine overhaul when I probably won’t be able to pull $3k out of the car once finished (salvage title, mismatched front bumper and crappy paint on the hood… drives well but it’s not perfect). Plus I already have about $2500 into it, so it’s just not feasible. Not counting all my hours of labor and diagnostic time… which I bill at $120/hr to my customers, and apparently I pay myself $0 on my flip cars 😂