An adapter assembly fitting an engine coolant system to covert the system to accept a threaded high pressure coolant line in place of the rubber hose, the adapter securing to each coolant line connections, including the upper and lower radiator necks, the necks on the water pumps and the neck generally leading to the intake manifold. These adaptors connect to each neck, allowing for further connection to the high pressure threaded hoses used in high compression engines or for those automobile owners who wish to upgrade to a more aesthetic appearance of the engine compartment. The adaptor assembly comprises a circular composite band, a body having a fluid channel, a split ring washer and a compression ring which attach to each neck in a manner to seal the adapter to the neck.