06 mazda 3 2.3 thermostat p0126
 

So I've read on many threads about changing the thermostat and I wanted to update on changing mine. Many posts say that it's required to remove the tensioner pully. I did mine without doing so and fairly easily. Drained fluid from the plug beneath the radiator and hoses connecting thermostat. Put a 5/16 on the end of an extention, connected it to the bottom screw then attached the wretch after. Was a piece of cake. Changed it on a p0126 code and as I replaced the temp sensor gauge around 5 months ago I was pretty sure it was the culprit.

I'd also like to ad that in order to drain from the radiator you'll need a short handled, wide head Philips as there is little space.