Van overheated.. I changed the knock sensor, changed oil and coolant still knocks ....can not excel over 20pmh or hear knocking / pinging. Recently changed thermo, distributor, adjusted timing, tune up and put B12 in Gas tank & used 93 Gas. Mechanic advised me to drive it fast to see if it blow out carbon / deposits... It overheated again !! I believe it's intake manifold.