They come in 175 deg, 185 deg, 195 deg....and are readily available....autozone, advance, oreillys all have them. When it's 30s and windy (i remember mempho being quite windy), engine heat dissipates quickly..I'd bet stuck open stat as others indicated.

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1983 300SD 307k miles
1993 Ford Escort Wagon 215k miles
1995 Isuzu P'up 214k miles