So I have a AST on my FC which is a different but effective way to quickly purge air from my coolant system. I have an issue getting two radiator caps to recirculate correctly. I thought I would steal an idea from some Nissan guys and plumb the relief/recirculating hose from my radiator to my AST. This would eliminate one recirculating path. Any issues will pressurizing both sides of a radiator cap?

Here's the Skyline setup



Here's Mine

 

You can use 2 caps but TEE the hose that goes into the Reservoir.

 

That is what I have right now. The problem is air gets in lines on one side of the system (AST or radiator) as the other side recirculates (checked using clear lines). I believe it's due to the loss of vacuum as one side recirculates and the height of my overflow tank (stock location, lower than ast). It's not allot but over time the overflow tank fills with the exact amount the system is low. FYI I've pressure checked the system.