[A26B]

Daniel,
That Mustang thread is full of BS.
The 3ea 1/8" holes only increase the total flow through the thermostat from the radiator to the engine. They also allow an incremental flow from the engine, through the radiator, through the t-stat past the thermal pill. The notches in the bypass valve on the t-stat also allow coolant to flow by the thermal pill to provide engine temp sensing to the t-stat, thereby controlling opening/closing of the t-stat valve.

What do the 3 holes do? As Sammy said, it will prolong warmup slightly. The benefit is to allow more coolant flow through the radiator during higher rpm usage. This prevents the t-stat bypass from operating as soon. When the bypass opens, coolant from the engine bypasses the radiator and goes straight back to the engine....hot.

The drilling of small holes does not affect the temperature regulation of the thermostat very much.

BTW, you cannot install the correct thermostat for the ZR-1 LT5 engine , backwards. It is impossible. If a thermostat was ever installed backwards in the LT5, it was the wrong thermostat.

This is a good time to offer a word of caution when buying a thermostat. I recently went through a real hassle buying one for a customer in Australia. Sure, Autozone & others show them, special order.. When my order came in, the t-stat "looked" essentially correct but it wasn't. No notches in the bypass valve. You can read more about this subject on Jerrys Gaskets under the thermostat part. I'm not trying to sell anything here, just want you yo know about it..