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Technical Curious Thermostat question

Discussion in 'The Hokey Ass Message Board' started by dkmc, Jul 27, 2017.

  1. On some Thermostats that have the small vent hole, they also have a rivet or some sort of metal 'widget' in the hole. Why? Why put the hole there then partly block it?

    Also, I've noticed if I drill even just one small vent hole, say 3/32" in a thermostat in a Chevy, when it's really cold, 10deg or less, the engine seems to take a lot longer to warm up
    than when there is no vent hole. Anybody else notice that?
  2. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    from Houston TX

    The hole is there to prevent a sudden surge of coolant and the engine cooling off too much. By allowing a small amount to go by the engine will heat up at a constant rate. People have been doing this forever, but some engine manufacturers including Kubota are acting like this is a new idea

    Sent from my HTC One M9 using The H.A.M.B. mobile app
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 44,018


    Perhaps the rivet is a check valve? or it might let air through quickly, but not coolant?

    Yeah, it does not take much coolant flow to keep an engine cool at really cold outside temps.
    dkmc likes this.
  4. I thought the hole was there to vent air when you're filling it initially?
    At any rate, I drilled a 3/32 hole, and then put a cotter pin in it to restrict it....why.....I really don't know.

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  5. The wiggler lets air thru upon filling.
    Once it sees water pressure the wiggler restricts the flow thru the hole.

    I thought I'd be smart and drill a tiny hole my wife's Thermostat on here late model. It's a pain to bleed and burp the air on it. Well that solved the bleed and burp issue so well I did it to my nieces car too. They both soon thru a trouble code that the engine was taking too long to warm up.

    SOOO , it's 100 proof that hole and the coolant flow thru it makes it take longer to warm up.
  6. Ha! Damn computers...
    But wow that's amazing proof! I wondered if it was my imagination.
    Hard to believe such a small hole could make the difference.
    I better use a rivet or a nail instead of a cotter pin, so they will seal off.

  7. Why not get one with the wiggler?
  8. Well,
    1. Forgot about the wiggler.
    2. It's not for a car so the auto parts people (Advance) are clueless.
    I took in the water neck to get a (thermostat) gasket, and the guy put the casting number on the neck in
    the computer....idiot. And that was after I told him it was John Deere.
    3. Already got the one without it, and drilled the hole.
    I could ask at NAPA, I didn't install this one yet.

  9. There's just a few different sizes of thermostats.
  10. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    from Wisconsin

    I've always used a 1/16 inch bit and never had a problem. Air goes through a 1/16 hole easily but not as much water will go through. Even if it takes a few minutes for the air to go through, it isn't a problem. A smaller hole would work too but 1/16 is the smallest bit in most sets.

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