Yes, that gauge is 100% a mechanical gauge. But the black wire in the block isnt a capillary tube, its a thermistor wire. The gauge works without power wired to it as its all based off the thermistor.
I had one in my K5 and the one installed on my LS in the K5. They are very simple but do go bad regularly. The red wire is to light up the gauge when the lights are on. If the gauge no longer reads a temperature, just replace it.
A quick search for the numbers on the gauage gave me this: Sunpro retro temp guage
UNTESTED, SOLD AS IS. GM General Motors. 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 second 2nd generation. F Body F-Body Chevy Chevrolet Pontiac Camaro Iroc Iroc-z z28 RS Firebird Formula Trans Am TA T/A.
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