I have just changed my thermostat and I am glad I did----somebody put an aftermarket t-stat in and as the picture shows the open area on full lift is about 25% less than the genuine Mazda t-stat.

Note also that this is a real "Made in Japan" one, complete with jiggle.This is available at your Mazda dealer,part no N3A1-15-171.You have to purchase the o ring separately doing it this way.

Note that part no 8AF6-15-171-9U (the one without the jiggle!)is NOT made in Japan,it is a part lashed up by MNAO presumably to save money.