The temperature was great with the stock radiator but it busted and i replaced it with a radiator from Napa. It's a brass copper and it doesn't seem to work as well. Everyone I talk to says the brass copper should work just as well but it doesn't seem that way. Any thoughts on this. That's the only thing i changed and I started having trouble with the temperature. I have no leaks, just replaced the thermostat, from Napa, and the thermostat on the oil cooler works.

 

The only thermostat that will work correctly in a 13B is the Mazda OEM one. Aftermarket thermostats always will have cooling problems

 

Did you put back all the little foam bits that seal the radiator to the cross bars?
This also helps airflow go THROUGH the radiator instead of AROUND it.


-Ted