Cat c15 Sdp air locking

My engine is doing something weird. I bleed the coolant system 100% then let it run a few hours or drive it and I'll lose heat in my cab. I go feel the plumbing and some coolant lines are cold and air locked again!

Compressor new, water pump new, pressure relief cap new, jwac deleted, no cgi, ard on it, old style oil cooler. No combustion gases present, tested with strips and the liquid test.

At full rpm and piping hot, it'll slowly climb to 10 or so psi in coolant tank.

Full engine rebuild 60k ago.

Gonna smash my head against a wall here pretty soon!

 

Not using any coolant, not pushing coolant out overflow either.

 

The lines clear, steady stream of coolant running through it.

 

Just replaced the compressor, no change. Pressure tested the system and no leaks, held air... gonna try again to be safe cause that lower rad hose has leaked a couple times in the past and I'm sure that's the suction side of the water pump.

 

I DO have a webasto bunk and engine heater. The engine one blew the gaskets so peterbilt took it off and plugged the ends and folded the lines over.

One thing I was thinking about is that the one webasto line is from the cab heater but the T fitting has the hose pointing upwards instead of down. I was wondering if it were causing a venturi effect or if that hose pointing up was having all the air trap in It.