I use NAPA coolant filters and bases in all of my vehicles, and recently I began to develop a small leak in the heater hose that comes off of the engine and runs into the firewall in my Caprice. The heater hose is a type that uses quick disconnect fittings on the core, and had apparently been messed around with during its life, anyway so I decided to replace it. The new hose has the correct restrictor in it to protect the heater core from coolant pressure at high engine speed. This is also the hose that contained my tee for the coolant filter base, leading to the filter. I relocated the tee to the area of hose before the restrictor, to give it more positive pressure, to ensure flow through the long hoses I had to use to get the filter system to a spot where it would fit. The mod was successful, and flow through the filter has been increased to an acceptable level. Doing this also creates a little more relief for pressure surges under acceleration away from the heater core, and allows a pathway for any escaping air bubbles at the back of the engine or steam, which would be recondensed on its journey through the long hoses, or escape from the radiator cap, near the return line outlet. Coolant is and remains clear. No more leaks, either.