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Hey there,

Bought a new Dayco thermostat for my NA8 from Repco. Part no. DT27A-BP.

It only has one valve in it (the main one of course). The Enthusiasts manual says when installing the new thermostat, make sure the smaller valve is at the top. I can't do this for obvious reasons.

I came across this at http://www.miata.net/garage/cooling_system.html

"Always buy original Mazda thermostats. The one that was in my car was an off brand, and it had only one valve, where the original Mazda has two. The Mazda one is a double thermostat, where the off brand was a single. The double always allow some flow to pass through the engine, and my car is now (almost) perfectly cooled."

I notice the photo of the one at Mania only has one:



Should I be worried?

Another lesser query I have is that Repco reckoned a rubber O-Ring goes around the circumference of the thermostat, in addition to the cover housing gasket. I was skeptical as wasn't one on when I pulled it off, but I bought it because it was only a few bucks. But looking at it now I don't know whether it's required..

The small hole above the valve allows a smaller amount of water to flow, so essentially no issue.

It's not as simple as it sounds each model had a different thermostat!

The na8 was the only one to get a sub and a main. All other models just got a main of varying size and temperature.

Have a read here http://www.maruhamotors.co.jp/miata/par ... ostat.html


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I see. Thanks for that link! Where do I get an NA8 specific thermostat?

You just bought one! Honestly the two valve model originally supplied with NA8s is a waste of time. If you're doing any track work or hot day spirited driving they barely flow enough. I've got no idea why Mazda bothered with them, but at least they quickly abandoned them.

The guy who said he fried his motor doesn't understand how cooling works in an MX5. When the thermostat is closed there's always a bit of safety by-pass flow through the heater core. He may have fried his motor but a single valve thermostat was not the cause, unless it was faulty to begin with.

marty085 wrote:Another lesser query I have is that Repco reckoned a rubber O-Ring goes around the circumference of the thermostat, in addition to the cover housing gasket. I was skeptical as wasn't one on when I pulled it off, but I bought it because it was only a few bucks. But looking at it now I don't know whether it's required..

There is no rubber o-ring.