Correct NB thermostat
 

Read through MANY pages in several threads, and found a lot of what's looking to be misinformation. The factory NB thermostat doesn't have a backflow valve like you'll see on NA cars, but DOES have a "Jiggle pin" to allow air to purge from the system. And is 190 deg., NOT 195 deg. as believed by many. After reading about a couple people having OEM thermostats show up DOA right out of the box... NAPA seems to be the best option on the market.

The first picture is from the Mazda Workshop Manual. The second is from a test I did on the NAPA thermostat. Third is the correct OEM part.

Greetings, BigCheeseStick.

When I first saw your name, I thought it was CheeseDick. No offense meant.

The early cars didn't have any sort of backflow valve. What you see there is actually a two-stage thermostat, wherein the smaller valve opens at a slightly lower temperature than the larger one.


https://www.miataturbo.net/attachmen...ine=1436655402

It's an unusual design which I haven't seen in any other car. The later Miatas use a conventional single-stage thermostat. When we do a coolant reroute on an NA, we typically discard the two-stage unit and replace it with a conventional thermostat.




A better view, courtesy of Arlington Mazda:

https://cimg7.ibsrv.net/gimg/www.mia...de83644f99.jpg

It's unbelievable the variety of stuff you can end up with from parts stores claiming "Perfect OEM match part". ORielly's has at least two different temps, and even a thermostat with the back flow valve that they list as "Perfect matches.". Rockauto is doing about the same. The NAPA part has been the only one I've found that's both the correct temperature and configuration for the NB cars aside from the dealer item. And I'm pretty pleased to see full flow by 205 deg.. With the reports I saw of the OEM part being bad or failing in only a few months service, it's just not worth the risk or price imo.

Read this:
A newbie's adventures in racing: Should you run a thermostat in Spec Miata?

I use a NAPA 180 - THM 101.

The THM 101 is a Stant part. My concerns with a 180 is I'm still using the stock ECU, and EGR. So it'd cause the intake to coke up, and the ECU would act up thinking the car never came up to temperature. Non-issues with a MS controlled track car though.

Cheezer, I'm still trying to figure out if there's some specific question / problem / issue that you're seeking to resolve, or if you're just venting. I have no problem with venting, just curious. We've done the whole "lets analyze various thermostats" thing a number of times here at MT over the years...


I very seriously doubt that a difference of 10-15°F in coolant temperature is going to cause exhaust gas to spontaneously precipitate carbon all over the inside of your intake manifold. Particularly since said manifold has no coolant running through it, and is quite thoroughly cooled internally by all of the air rushing through it.

We're talking about extremely subtle differences here. Loads of folks have swapped 180° thermostats into their cars, and no significant disasters have been presaged by this act.

Just trying to clarify the actual thermostat used in our cars. Everything I read here states 195, and depending which other sources you go to, it could be 185, or even 192, nobody actually has it right though (190). Then to look at the parts warehouses you could get any one of three different configurations that are claimed to all be oem to. :/

With these little engines dancing so close to boiling point, the coolant routing issues, egr passages clogging in the upper intake, add forced induction or track use... Using and recommending the right parts really matters. jmo

I have a stock ECU and had issues with a 160o on cold track days, in February, where it appeared the ECU was still in cold mode. I haven't had any issues since moving to 180.

If you want OEM, Rosenthal sells them.