Originally Posted by camaroman7d
Willys I see what you're saying but you are acting as if the thermostat is "isolated" from the hot engine water. That is not the case. It is sitting in the engine water so once the water is above the opening temp, it should open. Even if the water just above the stat is cooler. That would throw it off by a few degrees (delay the opening) but should not make the gauge peg before it opens. Could be a combination of things here. Very slow acting thermostat and a plugged bypass. This would make sense. Drilling the holes only cost him a few minutes of his time and it is worth a shot. If it works great, if not the real problem needs to be fixed. They didn't come from the factory with holes drilled in them and they worked.
Trust me, it works just like I described! Has nothing to do with air in the system or type of thermostat in place. Sure the thermostat is sitting in the engine water but the water around the exhaust valve is getting a WHOLE lot hotter sooner than the idle water around the thermostat sensing bulb at the front of the intake manifold. Water temoperature gauges are usually in the head where the water is getting hottest fastest and it reads accordingly, while a thermostat w/o circulation of the hot water past it is ignorant of what is going on. Eventually, there is enough gravity circulation of hot water and conduction through the iron (aluminum) that reaches the thermostat and it responds. If the water isn't overtly circulated past the thermostat, it takes longer time to get it going and you will ALWAYS get that scary peak in water temp just before the thermostat opens. Very scary but doesn't last long enough to do any harm. Happens with ANY thermostat- quick opening or otherwise. That's why they install the bypass at the factory. I first ran into this on my 235 in-line 6 in my '53 Chevy pickup. Bypass was inoperative and every morning my engine water temp would spike to +240F then instantly drop to 180F and stay there the rest of the day. I got around it for a couple of years by turning on the heater, but finally got off my duff and got the bypass working and no problems since. A couple of holes in the thermostat flange doesn't affect how it works but does allow the heating water to reach it and get it to operate as designed. Works fine but just not the BEST fix!