Low Temp Thermostat...
 

I found an ARC Low Temp Thermostat on rhdapan.com selling for $78 (ARC Low Temp Thermostat FC3S(Kouki). The item is a drop-in direct replacement for your OEM unit and ARC has made a special opening temp of 75 degrees Celcius for the 13B engine (all other ARC thermostats open at 68 degrees). I find the price insane when you can find an OEM Mazda replacement for less than $20. Has anyone had any experience with this thermostat and/or compared to the Mazda thermostat? Thanks!

Simple waste of money dude.

There is no gain in lowering the coolant temp on your rotary.

^ agreed.

Invest in a aluminium radiotor instead and only used OEM/Dealer thermostats! And DOUBLE CHECK BEFORE PUTTING IT IN THE CAR. (boil it in hot water :D)

Suitable for lower power and increased fuel consumption, already covered this topic this week
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/lower-temp-thermostat-890491/

¡GUAU! Exactly what you want for your sports car!