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  •  » Hot idle compensation valve

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    8/25/2019 7:48 AM  #1

    Nos681
    Senior 24-7 FYI Addict

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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,343

    Hot idle compensation valve

    Morning all.
    Reading some of the tuning posts recently reminded me to ask.

    How does the “hot idle compensation valve” work?

    From examining it...in an older repair manual...it appears to act as a relief valve if gases build up excessively.
    It was plumbed in-line with pcv valve on my ‘65 when I purchased it many moons ago.
    Back then, no one knew what it was for and never found it in any repair manuals.
    Even the recent repair manual shows it but doesn’t describe its operation... it did describe pcv operation.

    Since I cannot post pictures, I will describe it.
    It’s a brass tee fitting.
    The inline taps go to carb spacer and pcv.
    The branch tap has the check valve...kinda a combination of clothes hanger pin operation and the seat like a carburetor float bowl...the spring is two pieces of flat brass clamped together to keep valve seated under normal vacuum conditions.

    Inquiring mind would like to know.
    Have never seen it on any car since.

     

    8/25/2019 9:52 AM  #2

    RV6
    Senior 24-7 FYI Addict

    Offline

    From: Pine Junction, CO
    Registered: 3/01/2016
    Posts: 1,250

    Re: Hot idle compensation valve

    Here is what I found on the interweb.

    When the ambient underhood temp increases to a certain point the bi-metalic strip on the hot idle compensator opens a rubber needle - brass seat metered orifice, causing what is essentially a vacuum leak of a predetermined amount into the intake system.  This extra air will in turn cause the idle speed to increase, moving more air through the radiator and water through the cooling system due to increased fan and water pump speed the result being  the motor will cool down to the point where the ambient underhood temp is lower, and the valve closes and the vacuum leak will stop, returning the engine to a normal idle speed.

    Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
     

    8/25/2019 9:43 PM  #3

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,343

    Re: Hot idle compensation valve

    Thanks Gary!

    This was a San Jose built car.
    Now...does anyone still use this?
    Or past practice of its use anymore?
    Was it used nation wide or areas prone to heat?

    Just wondering...for 20+ years.
    Heck, it took this many years to get an explanation of how it is “supposed” to work.
    I LIKE THIS PLACE!!😁

       •Thread Starter
     

     

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