Carl is probably best to chime in on this because he works at a dealership but my experience with thermostats is that at most places, including dealerships, you will find aftermarket producers such as Stant dominate the market. I dont know for certain if GM ever actually manufactured their own. They are available at Canadian Tire, Piston Ring, NAPA and others. Thats where I buy them for my engines. They havent changed in the 45+ years Ive been buying them, except maybe for the holes they have drilled in them to allow a low volume bypass of sorts which really helps to avoid air locks in the system. Never had a problem with them.
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72 Nova SS, 66 Beaumont Sport Deluxe, 09 Pontiac Solstice GXP Coupe
Hmm, I see that. I'll have to check for changeups. I'm quite sure I got a 180* for my 427 when I built it. I'll try to look tonight to see what I bought.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
