235 Chevy Thermostat Shoots up to over 240 and then back to 180 Deg

Discussion in '1947-1954' started by mockoski, Nov 1, 2019.

  1. mockoski

    mockoski Member

    Jul 14, 2014
    Hey guys,

    I recently installed a heater in my 53 Chevy Pick up. I drained the radiator, and installed a new 180 deg thermostat.

    Since then, the org. gauge shot up over 220, and eventually broke the gauge. I installed a temporary gauge and see that when I first run the engine it shoots up past 240 degs and then will shoot back down to right around 180. While driving it will go up to about 220 before the thermostat opens up.

    I first thought it might be an air pocket, but I did burp the system ( at least I thought I did.. by leaving the cap off until I got some fluid coming out of the top radiator then placed the cap back on). But the temp gauge still shoots before the Thermostat opens up.

    Also, the thermostat that I purchased already had a pre-drilled hole in it (with a little brass jiggly thing in it), so I thought that hole would be enough. Perhaps another hole?

    Anyone have thoughts about what would be causing the thermostat to not open up until the temp gets much hotter then it should?

  2. Chiro

    Chiro Member

    Sep 3, 2006
    Long Island, New York
    Could just be a bad thermostat. I had some issues with one on my flathead V8. Take the thermostat out and test it on the stovetop with a pot of water and a thermometer. Replace it as needed. The pre-drilled hole with the jiggly thing is adequate to burp the system. I drilled 1/8" holes in my thermostats for the flat V8. Replaced them both recently.


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