I stumbled onto something a little while back. My 153 setup has no heater system at this time, (I'm working on a neat little Allstate heater box) and I had looped a hose from the water pump to the return on the thermostat housing. I wasn't running a thermostat, just the ring from an old one. If you loop the heater circuit you recirculate un-processed HOT coolant right back into the engine. The volume is roughly 1/4 to 1/3 of the hot liquid right back into the engine!! Not the best thing you can do when your cooling system is marginal. If you're not running a heater, plug the circuit. If you ARE running a heater, I'd suggest using a positive shutoff heater control valve.
I also found that on these engines, you just about HAVE to run a thermostat. I've got a Cadillac CTS-V radiator and two electric fans as well as a big free standing transmission cooler, but it ran hot with just the restriction ring in the T-stat housing. I installed a 185 degree unit and the problem went away. It went from running up to 260 degrees to running just 190 on the average. The thermostat keeps the coolant in the radiator long enough for it to cool down. I'd never encountered that before, even though I once ran a radiator shop for several years.
Last edited by Blackwater; 05/28/16 01:50 PM.
