Doubt a small hole will accomplish anything. Some thermostats come with a hole to aid in letting trapped air out. If your doesn't have one it sure won't hurt. It is possible you have air trapped but you might have a bad head gasket or crack and exhaust is being pushed into the cooling system.I ran the temperature trace this weekend and also monitored the sensor voltage to the instrument gauge. It shows the red line spikes are start-up and stablized after about 8 minutes. My white smoke is pretty brief now, I'm guessing my oil and filter change may have helped.
Here's the link to the graph & pictures. Let me know if this helps with the troubleshooting. One person had suggestion drilling a small hole in the thermostat to allow fluid to circulate all the time, and in my situation at start-up. I can see how that could fix my problem, but if there's something bigger going on I'd rather not temporarily "mask" it unless this is normal or a known design issue.
I ran a 150hp tractor for years with exhaust pressuring the coolant system to the point where there was a blast of air coming out the rad overflow. Finally fixed it but never did any harm. With yours though you are getting temp spikes at startup which means you have a leak likely right at the sensor which creates a pocket of no coolant for a period of time. You probably won't hurt anything but then again......Might want to fix it sooner than later.I think I figured out the root cause of the temperature spikes...
When starting up the tractor the other day I noticed the radiator overflow tank was bubbling, but it was cool to the touch so it wasn't boiling. When the thermostat opened and coolant circulated the bubbling stopped. Looks like I have a head gasket leak? I took the overflow hose and put it into a bucket of water and confirmed that exhaust gases were leaking into the coolant. I'm going to assuming the temperature spikes at the sensor are due to the exhaust gases and aren't actual engine temps.
I guess the question is - if my temperature is stable when using the mower, no white smoke after start-up, and the bubbles stop once the coolant is circulating, how important is it to get this fixed ASAP? I would probably leave this repair up to the shop ($$$?).