Thermostat Selection

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 77JimmyMan, Jan 31, 2002.

  1. 77JimmyMan

    77JimmyMan Registered Member

    May 16, 2001
    Likes Received:
    Southeastern MA
    Im about to put the motor for my 77 Jimmy back together. Its going to be running about 9.5:1 compression with newer 93' up truck heads that have 64 cc chambers (10110810..93-up..350..Gen. 1) vs the 76cc of the old heads. Im going to use an GM aluminum intake of of a 87' Firebird. There was a 195 degree thermostat in my truck. Would I be better off running a 180 to keep the temp down with the higher copresion? My dad says to stick with the 195 saying that the newer trucks run hotter for better combustion. But i think id be better of with the 180 just for fear of detionation, not having fuel injection and a computer to retard timing if needed. Also is it worth while to block off the exhaust cross over to keep the manifold cooler? My carb has an electric choke and theres no EGR. Any feed back would be great. ~Mark~
  2. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
    Likes Received:
    Roy WA
    I'd say run the 195. If running 195 doesn't work, run a 180.

    The ONLY thing I would be concerned with is if you have problems with pinging related to temperature. If your cooling system can keep the motor at 180, it can keep it at 195. As long as the coolant reaching the heads is cool enough to keep them from causing ignition problems, a 195 is, IMO, optimal.

    I wouldn't have problems blocking off the crossovers, I am willing to bet the heat from conduction is plenty to keep the carb warm, since you won't need it for choke. I've heard problems with the carb "icing" after an extended freeway run, but I really think that is an exception, especially running a 195 thermostat.

    Again IMO, you want cold air entering the engine, but a lot of people try to achieve that by keeping the intake cool via thermostat. Cold outside air with a 195 thermostat is my ideal setup.

    I think a 195 thermostat has been pretty much standard in GM motors for about 30 or 40 years now.

    One of these days I will dig it up, my dad mentioned that he has a book that mentions an actual GM thermostat/dyno test with big blocks, and the power difference with different temp thermostats was negligible.

    My tech/links page: <a target="_blank" href=></a>
    Why insist on counting when the ring gear has the tooth counts stamped in?

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