So your temps say that the inlet to the Hx is only 179, so you cant expect that your storage will go much higher than that. Plus you are only dropping two degrees, so you arent even dropping much heat in there. I dont think its a pumping issue at this point. If you can figure out how to get the inlet temp into the Hx up, thats the first step I would think.
EDIT: Or am I reading this all wrong and you are trying to bump the temp of the outlet to your radiator loop?
EDIT: Or am I reading this all wrong and you are trying to bump the temp of the outlet to your radiator loop?