My cooling system has an issue and I'm going bonkers trying to figuire this out. Some basic info;
2005 LGT MT
18G blouch FMIC
The motor has 50,000 miles since the rebuild, Woosner 4032 pistons, mild head work and new bearings, oil pump, etc. Nothing crazy. The car runs perfect and does not use any oil (I know, impossible for a Subaru but true)
Here is my problem. About two months ago when I start the car cold I could hear water sloshing into the heater core, air in the system. I bled it and it kept happening. Then I noticed an antifreeze smell, there was coolant in the underbelly splash shield but pressure testing with both a hot and cold engine revealed no leaks. I filled it again, added ultraviolet dye and found the coolant is puking out the overflow bottle at times (overflowing). So what I observed was when I drive the vehicle under high load conditions the cap on the turbo coolant tank was dumping coolant into the overflow, a lot. If I drive like a normal human, after filling and completely bleeding out all the air the coolant tank level rises normally and the drops as the engine cools, as it should. But if I jump into boost for a few miles before I get home, after I shut it down the coolant inside the turbo line (the top one that goes to the turbo tank) is boiling. I can hear it and feel it, and the boiling coolant is going into the overflow. Then it won't suck it all back in and I get an air pocket again.
Repairs done are;
Pressure testing and leak testing- inconclusive
Hydrocarbon check of the cooling system, not one ppm of HC detected.
Thermostat and gasket (Subaru)
Both Radiator caps replaced, genuine Subaru.
Full drain and complete non-chemical flush of everything, including the heater core and engine block.
New Radiator, a double row GMS full aluminum unit.
New upper and lower hoses, all new ancillary hoses from tanks to overflow.
I was thinking maybe there is a crack inside the plastic turbo overflow tank that opens up hot and bypasses the cap into the overflow but this is a long shot. I'm running out of ideas, any input is much apprecieated.