How come the coolant in the recovery tank will not return to the radiator?
What is your question?
I have replaced the radiator,hoses,cap,thermostat,pressure tested the system and it was within spec.,leak-down test the cylinders,compression tested,tested block for hydrocarbons and all was fine so what else can it be?
The bottom line is you have a coolant leak somewhere. The cooling system is a sealed system. Meaning that when it is hot it dumps any pressure over the system pressure limits into the reservoir. When it cools down the contraction of the cooling system sucks the coolant out of the coolant reservoir and you cooling system is working properly. If you have to add coolant to the reservoir then you have a leak. Coolant does not evaporate.
There has been no overheating and the temp gauge remains perfect this has just started in the last month,I check the levels before I start the car and usually pump the over full over flow back into the radiator,The cap is brand new from Subaru and all hoses are new and double checked.
Check the seal of the hose that goes between the radiator and the reservoir, make sure the cap is not faulty, might need a better quality radiator cap.
I replaced the cap with a Subaru cap and I even exchanged that cap for another.
It has come down to the heater core,It is hard to check for a leak.
Could it be that some of the spring hose clamps are failing? What type of hose clamp is best?
I have tested the compression and did a leak down test 4 times with a block test after every test with no change in the color of the test fluid.........
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I haven't had to add coolant I just pump the over-flow back into the radiator with minimal lost