I never heard of this before. Has anyone did this?
 

Talking with a guy at the local cruise night. I was explaining to him how I would like to lower my engine temperature. It was running about 200 degrees that night driving to the cruise.

He said I should drill an 1/8" hole through the flat side of my thermostat. It would be a small bypass.

Is this an old trick? Does it work?

Let me know.
Thanks
FB66

People generally drill the hole to avoid air pockets when filling the cooling system. It may cause the car to run cooler in cold weather (I drilled the hole on my daily driver once), but you probably won't notice a difference during summer cruising. You'll have to check the basics - radiator condition and size, fan and shroud, ignition timing, etc.

IMO, i would say drilling a hole in the thermostat does nothing for cooling as the thermostat is already open. As mentioned the hole help remove air from the block/cylinder heads when filling the rad. You can always remove a pipe plug on the crossover and achieve the same results.
Take you thermostat out and test it and make sure it opena at the set temp marked on thermostat. What temp stat you running.? Also try a 160 deg stat see how the car runs. Buy yourself a good stainless steel unit from Napa. (Napa Premium) Timing, fuel curve, rad size, fan blade, gauge that is reading temp, thermostat., water pump, pulley size, how engine was built. Lots of stuff at play here when it comes to engine temp.