The GF calls Wednesday afternoon, on her way back from Jacksonville, she's on the side of I-95, 100 miles north of here, with a pegged temp gauge in the Miata. She was running around 75, A/C quit, she observed water overtemp and shut down.
OK, let it cool off a bit, coolant level, w/p belt, electric fans all OK. On my advice she ran it again for a mile or so, overtemp duplicated.
After a $250 tow down here (not bad price actually), I figger it's got to be something to do with the thermostat.
Hmmm...
(picture below)
That stainless steel pin *FOD that's wedged in there is completely binding the action up & preventing the 'stat from opening, even in boiling water!
The source of the *FOD I suspect may be from the failure of a radiator cap, in a former life, ie the center pin. It must have migrated from the top header down the top hose and just hung-out down there in the T/stat housing, just waiting for the right time to strike...
Fortunately as soon as the thing started to get hot, the A/C high-side overpressure switch kicked the compressor off and got her attention, and she's had enough stuff break on her racecar over the years so she shut down RFN...
(* for everybody but Jim M.... FOD = foreign object damage, anything that's somewhere that it's not supposed to be, that ultimately screws something else up)
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