Coolant/Thermostat/Under Cover Valence

[atlex]

There's nothing wrong with a motor running as high as 220F, with the system up to pressure a motor can run safely over that. They're _designed_ to operate at these temperatures since the 50:50 Coolant mix is designed to pressurize which increases its efficiency and the boiling point changes to be higher than the 223F, at 15 PSI it's actually more like 268F. that's a touch over 40 degrees of 'headroom'. 'Don't open while hot' means something on the rad cap. Ne touche pas, Baka ! Because if you open it while hot the engine might be over the atmospheric boiling point, causing it to quickly boil the coolant when you ignored the warning and undid the cap.

As Greasemonkey2000 states, the point of the thermostat is to get the engine up to peak efficiency (temperature) as quickly as possible before then allowing cool coolant to flow into the motor, and this can show you hitting 220F or a touch beyond as the coolant pressurizes prior to the stat opening, and again, there is nothing wrong with this behaviour. The coolant system of the miata, while not as perfect as is could be (transverse engine origins..), has proven to be extremely reliably engineered for normal use. Thermostats are a service item, not a weak point in the Mazda engineering.

The undertray's cooling function is to increase/stabalize a low pressure area under the car, which helps draw air through the radiator, past each side of the motor and the transmission tunnel. Without the undertray you basically generate excess turbulence under the car. In fact there is a mod that can even lower UBTs over the stock undertray/setup by adding a small upside down gurney flap at the end of a cut OEM undertray, because it increases the size/immediacy of the low pressure area I've just described.

https://rev9autosport.com/nielex-und...r-end-lip.html