Symptoms;

Coolant overflow tank beyond full (stays that way all the time. to the point of coming out the cap. Radiator NOT full.

Upper radiator hose collapsing (pinching off) during cool down. Pops back when radiator cap is removed.

Both the hose in question, and the radiator cap have been replaced.

Any ideas what might be causing this?
The xB has 339,000 miles on it. Did have a coolant loss (added stop leak) some 35,000 miles ago.

Thanks in advance

 

WOW. 339000 miles? That's crazy awesome! I might not be much help on this. Have you checked the hoses are they cracking or worn? If so may want to have them replaced. You said that you added stop leak, have you had a coolant flush recently if not then that maybe an idea. Let us know what you find.

 

That is a lot of miles - impressive.
Your engine is trying to do the right thing by pulling the fluid back into the engine on cool down, but something is stopping that from happening - hence the collapsing hose.

You say you replaced the radiator cap, so we will start from there - check the hose going to the overflow tank for blockages and check the tank for something sitting in the bottom that would get sucked back into the hose when the engine is cooling.

You can buy an $8 generic expansion tank from autozone, which has some hoses inside it and a bracket kit. You can plumb this in while you figure out what is wrong with the stock system. You will have to drill a hole in one of the 3 spigots that you put the hose on.
http://idqusa.com/?s=MCR-3
(Autozone didn't have a picture, this is the manufacturers site)

 

Hi, on a 2004 Scion xB, I had a similar symptoms. Last year of 2019 this car saw three garages and got five diagnostics: 1. Leaking water pump; 2. Blown engine gasket; 3. Bad radiator hoses; 4. Damaged front radiator; 5. Engine has uncontrollable deviation movement in the time of acceleration.

All diagnostics were free. I start by replacing the Engine mounts x3 (all) to solve the diagnostic #5. After this, no change. After replacing with the wide band clamps and new silicone radiator hoses, for #3. the symptom was there again. Then was replace the front radiator and the cooling electric fan/motor assemble.

Here we find other problems:

There is a small hose that go on the right to the side tank/overflow. This had inside about 10" (inches) of kind of glue/cement or so. It was possible that the engine was running on high temperature and/or high pressure. After fixing and replacing #4 diagnostic, the symptom was still there.
I install a heater core by-pass, and the engine gets to run in parking for 20 minutes. I saw few drops under the car in the vicinity of the water pump. Because this last test was confusing, I drove about 50 miles on the highway.

Next day I try again (with cold engine) by idling in the parking lot for 20 minute (with no rain). Can not be seeing red color liquid on the cardboard. Also no other fluids on the floor. I was looking to the exhaust pipe performances on the smoke color.
The color was not dark and not blue, was more like steam clean. I was surprised to see that no radiator coolant need to add. I connected back the heater core, and no problem yet.

As of February 2020, still checking every Morning and looks OK the coolant level in the radiator.

I purchased the water pump, thermostat, and I am ready to replace if is needed.

____