I would think that if you don't have a recovery system, you will most likely always have air pockets. When your car cools, isn't it sucking air back into the system through the cap port? If that air pocket is under your temp sender, that could be the source of erratic readings. I bought a cheap catch can from Jegs, ran a tube from the top cap expansion tank port to the
bottom of the can (behind the can in the pic) with the petcock open and a tube from the top of the can to outside. Never a problem.
