Guys, I'm out of ideas, need help

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.

Fans are cycling on / off?

Funny thing is the temp gauge NEVER goes above normal unless I neglect to keep filling it and the level drops low. I can do three wot quarter mile runs and the temp NEVER rises unless the coolant level drops. When I bleed and refill I wait until the fan cycles twice before I put the caps on. It can idle all day and never reach a half on the gauge.

When I bleed and refill I wait until the fan cycles twice before I put the caps on. It can idle all day and never reach a half on the gauge.

Incorrect fill procedure. You probably have a pocket of air that is moving through the system. As the system cools it will give back/take coolant from the res.

Fill it up (slowly, you can also squeeze the upper and lower hoses to burp/cause a siphon). Run it until the fans cycle. Let it cool. Check level again and add as needed. Repeat.

This is why we use a very expensive Snap-On tool at the shop to fill systmes. I actually pull them into a vacuum pre-filling. When I crack the valve, the vacuum pulls the coolant into the system. No air. EVER.

I have the tool you are refering to. I never once had to use it, I always raise the rt side of the car and bleed as stated above and never had a problem. Not just my car but the hundreds I have worked on. I bought the tool for Jeep 4.7 and 3.7 motors, those go airbound everytime you drain and refill.

However I am at my wit's end so I will give it a try. Mike, do you think I should completely drain the system? Which cap opening are you attaching to?

I go for the highest point (so the turbo coolant res). I also have the good old Lisley spill proof "funnel". That also works great. Put it on the turbo res, leave the rad cap off until you see the coolant getting close and cap it. Then add until it is full, but squeeze the hoses to bleed/siphon as plenty more will still go in. Heat it up until the fans come on. Let it cool. Check level and add as necessary. I should note that I perform this work with the car level and on the ground.

I have had my 02 Bugeye get air bound. It had only a rad cap on the turbo res (none on the radiator). Without the second cap, it can be a pain.

In your situation, I would just drain the radiator to "start over".

I'll try the vacuum method, as you stated. Im not sure if I have the correct size cap adapter for the siphon tool (jeeps use a big cap) but I'll buy one if I need it. Thanks for your input. I just am bewildered because I've had this sytem opened at least 2 dozen times over the years and never had a problem with this.

I should never say never, I know better having done this all my life.

Trust me, when my bugeye decided to trap a bubble it was more than frustrating. I had to drain it down 4 times, then finally leave it overnight in order to "burp" it. I cursed the single rad cap system for hours. Anything is possible. Everything that can go wrong, eventually will.

Problem with the turbo, making the turbo very hot causing that line to boil? Just an idea im a noob. Hope the vacuum fill works for ya sounds like its been a nightmare.

Originally Posted by Bochim

Problem with the turbo, making the turbo very hot causing that line to boil? Just an idea im a noob. Hope the vacuum fill works for ya sounds like its been a nightmare.

Yes, the top coolant line from the turbo has boiling coolant going into the coolant tank when I shut the car down, worries the fck out of me but if there is air caught in there I'm sure it would cause it.

If your sure you have all the air out, I can't see why you of all people can still have air in there. (Your not new to this), then my guess is HG or cracked head.

You say it only happens under high load, which = boost.

I'm scratching my head Max, I have done an HC test several times both with an emissions analyzer and with the block fluid tester kit. All have been inconclusive finding any HC in the system. I am still wondering if the plastic turbo tank has an internal crack or something. Needless to say I have to try what Mike suggested, just called the Snap on guy for the adapter today.

Do you see fluid around the tank after boost ?

I know you said you saw it coming out of the overflow, but that is normal for a HG leak.

Have the heads had a lot of porting done to them ?

Hopefully it is something simple like a tank, but I know about denial, I had a hard time admitting to sinking sleves in our first 500+ whp honda 1.6L. I even replaced 5 HG's over the summer so we could keep racing the car. Yea, call my insane...

The girls at Cometic began to know me by my first name. lol

No external leaks what-so-ever. Heads were port matched, thats all. No HC's in the coolant tank even if I check it after shut down and the hose is sending bubbles in there. I wonder if a crack in the turbo housing would cause this, or if that is even possible?? Denial, my best friend lol.