Coolant not returning from overflow tank 06 H6

[MeoW71]

Trying to figure out why the coolant is not being pulled from the overflow tank after the car sits overnight. I've done the following: Replaced radiator cap, checked overflow hose (and put 45 degree cut on end per a tsb) and searched for obvious leaks.

 

 

I'll say that the overflow tank apparently gets filled to the top and overflows when I do extended highway drives, but that doesn't happen when just drive around the city when doing errands.

 

 

 

It doesn't look like coolant is being lost anywhere, because when I pull the radiator cap and look it, it's always at the same level, except after a highway drive and its puked out from the overflow tank.

 

 

The one last thing is, 90% of the time when I open the radiator cap to check, it's like a vacuum seal is being broken. There is a pop, and sometimes I hear the sound of fluid moving briefly.

 

 

Just looking for other things I could check, or possible solutions before I take it to my mechanic.

 

 

EDIT: Just to add. Hoses are firm when the engine is warmed up. However, I do hear the brief sound of fluid moving under the dash when I start the engine cold. The only time the fluid level drops is from the previously mentioned highway cruising where it pushes even more fluid into the overflow tank.

Edited August 5, 2021 by MeoW71

[Infosecdad]

I would make sure you have two new OEM caps, radiator and turbo tank.

The one with the ears goes on the turbo tank, the one with no ears goes on the radiator.

They are different pressures and shouldn't be mixed, and aftermarket caps have a history of not behaving properly.

 

Edit: Sorry, was going off the "2005 Legacy GT Wagon" in the profile, thanks Max

Edited August 5, 2021 by Infosecdad

[Max Capacity]

He's talking about a H6 engine.

 

I'm thinking you have an internal leak, may be caused by a crack somewhere ?

 

Might be time to have the system pressure tested.

[All_talk]

I'm with Max on this one, a small leak in the system can keep the vacuum from forming as the coolant cools down and it wont pull it back from the recovery tank. If that leak is someplace like a head gasket it could explain your highway overflow problem.

[SubOperator]

Hope I'm wrong but this sounds 99% headgaskets. Started with same symptoms on Tribeca, and I went through same motions of replacing the rad cap, cutting the hose end, etc...

 

 

 

You can buy a test kit to check for exhaust gases on coolant.

 

 

 

I followed a very detailed thread for H6 HG replacement on sb9t . com and did the work myself. Put 70K or so on it since.

[MeoW71]

Well, I went and did a pressure test. No leaks detected when I pressurized the system. I let it sit around 10min at ~16psi and the needle did not even move. I even did a dynamic test after releasing the pressure and the needle didn't move from the bottom.

 

 

I have two OEM radiator caps and they both tested good.

 

 

The only odd thing that happened is when I removed the radiator cap this morning after letting it sit overnight (+10hrs). There was the sound of fluid running and I actually had some fluid spill out.

[08SpecB_DE]

Unfortunately, coolant spewing from the overflow only means one thing, headgaskets. You can buy a headgasket tester if you want to confirm, but make sure the car is close to operating temp before testing.