Coolant flowing back into reservoir while burping COT

[dmjarosz]

What the titles says... I heard some gurgling while driving the other day so i figured id check the COT for air. I elevated the car on ramps on a sloped driveway so definitely had enough inclination. I added about two quarts to the COT bleeder hole before I realized it was filling up the reservoir. Reservoir cap was on tight, no coolant leaks or wet spots anywhere else on the car/ground What did I do wrong or where Im I relieving pressure to allow coolant to flow back? Im thinking start with new radiator cap since its original. Thoughts?

[03Merc]

You have to open the COT in the morning or when the car is completely cool. First make sure the reservoir is full and leave it capped off. Then open and Fill up the COT with a funnel till it stays full in the funnel, start the car and put the heat on defrost and floor if You want and run the car till it gets to 180 or so if You can, squeezing the upper radiator hose getting the air out thru the funnel, keep the funnel full. Once it's at temp shut the car off and make sure the COT is full and cap it. Let the car cool for hours, the more the better. Then only open the cot and fill it up if it's low. Then cap it and you're set. Easiest way to make sure the system is airless.
https://uploads.tapatalk-cdn.com/20200516/c77a3d7a8aaac1e037ca99bf0a79ad 90.jpg


Sent from my iPhone using Tapatalk Pro

[RubberCtyRauder]

Resorvoir cap could be bad

[dmjarosz]

New cap ordered. Fingers crossed

[Turbov6Bryan]

Next time just fill the reservoir to the full mark, then pinch the large coolant line below the reservoir. Then you can proceed without over filling it. Remove the clamp once the heat cycle and squishing of hoses is done. Make sure to run the heat and squish the hoses to the heater core. Put the cot plug back in and then remove the clamp.

[dmjarosz]

I replaced the coolant tank cap with new OEM and and the problem went away. COT is now topped off and free of air.

The old coolant tank cap held pressure so Im not 100% sure it was the problem but I'm not about to argue with success.