Hitting the Easy Button: Miata Heater Core Replacement DIY October 09 2013
I put this one off for quite some time, and frankly it was because I loathe these kinds of projects. The heater core went out sometime in mid December and spewed deliciously sweet, steaming hot, coolant all over my legs. Since then I've simply removed the heater from the cooling system as a sort of punishment for her bad behavior and frankly, it didn't get cold enough to need a heater in Texas. But enough was enough, and after fighting off the desire to just strip out the HVAC system (she's a sophisticated lady) I finally decided to bite the bullet and just get it over with. Just in time for spring, but hopefully this DIY will be much more useful to you now that the weather is actually cooling down.
Most of the other write ups involve the torturous process that is removing the entire dash; nightmares of broken plastic tabs kept me turning in bed at night. But I figured out I could do it without pulling a single tab, and I was right.