sounds like the same problem im having ill drive my 68 dart with a 360 for ten minutes and it will slowly climb in temp and itl sit at 160 for a couple minutes then 180 then 200 and it will run at 205-210 just driving around no stops-this scares me as it will not drop once its there and when i sit at stoplights itl get to 215-220 when i shut it down and push it over. Ive tried everything pump, stats/no stat, electric fans, flex fans with shrouds and ive even threw in an aluminum radiator months ago, no change and its been going on since i put in the 360 in a year ago just dont have the time to work on it as im stationed far away from home, hopefully you solve your problem and maybe itl help me out too, good luck