my temp. keeps rising from180 to 230 holds there for awhile then falls back to 180 . I recently replaced my water pump with a flow kooler pump ,new therm. housing .new robertson stat. new radiator cap ,new hoses flushed radiator . thought it was air locked . ive blead the heater coil and lines. still doing it .it not red lineing . this happens at speeds of 55 to70. any ideas?