1990 Toyoto 4Runner Water Leak

Found intermittent water drip on sons 1990 Toyota 4Runner V-6. Appeared to be coming from thermostat area and only only dripped when car was cold. I replaced the thermostat & o-ring. Problem continues…again only when cold. There is a small 3/8" rubber hose coming from the block side right behind the thermostat housing and traveling to another device mounted on back of block. What is this? Maybe this is actually where the leak starts although the hose looks good…I added a new ratchet hose clamp just in case. Leak continues. Advice ?

Thanks, Carmen