I have a 64 1/2 coupe with a 289. The radiator will take spells burping the water out of the overflow...so much sometimes that when you take the cap off you can't see the water level in the top of the tank. But, it doesn't do it all the time. I've tried 4 different 180 degree thermostats, new bypass hose...even a new three row radiator and two different new caps! It doesn't overheat and the heater works great. (The past couple of weeks here in WV have been 95 plus...while sitting in traffic the temp guage goes over about three quarter...it usually runs on the first line and only moves no more than half way...but this is the hottes weather we've had in the two years I've owned it.) I have a three core radiator with a six blade fan...any ideas?