check rubber hoses, sometimes they can swell inside restricting flow or kink where they make a bend but look OK on outside--check thermostat-might be stuck open or missing--if all that stuff is OK and its not the convertor--airlock is possible--fill system with coolant run with cap off till hot--install cap at first notch and run at half throttle for awwhile and remove slowly with rag on cap--this wiil burp any air