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Thread: Why does my fuel gauge fog up

  1. #1

    Why does my fuel gauge fog up

    What the title says, any ideas please?
    Clyde Boyer



    1972 2.5ST Coupe LHD Replica 5 speed.
    1972 2.4T/E Coupe LHD US 5 speed 69,000 miles from new
    1973 2.4E Coupe RHD Aussie 5 speed
    2007 C4S Coupe RHD Aussie 6 speed.






    Early S Registry Member #294
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  2. #2
    Senior Member
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    There are theories that it’s the proximity to the door window that ages the rubber seal between the glass and the body of the fuel gauge. Causes the seal to dry out and allow moisture to build up in the gauge housing.

    Some say, take apart the gauge and install a small desiccant cartridge, often found in a bottle of aspirin or other pills. To me, that’s a band aid fix. Not a cure. Best bet it to clean the glass, replace the rubber seals and make the gauge air tight again.

    Also some theories that glass isn’t perfectly clean is more likely to fog up.

    I’d be very curious if the clock on your RHd fogs up. Or maybe it’s still the fuel gauge.

    The other theory is that the gauges with removable gauge mechanisms (gas, oil temp, oil pressure and oil level. Are more susceptible to fogging because there are more places to air and moisture to enter.
    looking for 1972 911t motor XR584, S/N 6121622

  3. #3

  4. #4
    #2922
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    Sweden
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    I picked together a nice working clock from one nice looking and one working.

    The working one had no paint on the inside of the housing, it was just plated on the inside. The clock had a lot of micro-dust (white rust) from the corroded plating on the faceplate and the glass looked faded.
    The nice looking one had paint on the inside of the housing and everything looked like it was new.
    Light Yellow -74
    @lagteknik

  5. #5
    Quote Originally Posted by blucille View Post
    There are theories that it’s the proximity to the door window that ages the rubber seal between the glass and the body of the fuel gauge. Causes the seal to dry out and allow moisture to build up in the gauge housing.

    Some say, take apart the gauge and install a small desiccant cartridge, often found in a bottle of aspirin or other pills. To me, that’s a band aid fix. Not a cure. Best bet it to clean the glass, replace the rubber seals and make the gauge air tight again.

    Also some theories that glass isn’t perfectly clean is more likely to fog up.

    I’d be very curious if the clock on your RHd fogs up. Or maybe it’s still the fuel gauge.

    The other theory is that the gauges with removable gauge mechanisms (gas, oil temp, oil pressure and oil level. Are more susceptible to fogging because there are more places to air and moisture to enter.
    I think the theory does not hold up as clock is fine in my car
    Clyde Boyer



    1972 2.5ST Coupe LHD Replica 5 speed.
    1972 2.4T/E Coupe LHD US 5 speed 69,000 miles from new
    1973 2.4E Coupe RHD Aussie 5 speed
    2007 C4S Coupe RHD Aussie 6 speed.






    Early S Registry Member #294
    First Aussie R Gruppe Member #366
    TYP 901 Register Inc #6

  6. #6
    Senior Member dirk07's Avatar
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    Stuttgart, Germany
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    Had the same problem here today. Drove out of the cold garage into the sun and the tank gauge fog up

  7. #7
    Senior Member
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    Mar 2017
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    Orange County, CA
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    285
    same thing happens in my '82 SC

    and it is weird that it is just the fuel gauge that does this
    Last edited by myflat6; 06-23-2022 at 04:50 PM.
    Bill

    Early 911S Registry Member #4087
    Instagram: @myflat6

    '72T hotrod 210 0228
    '82SC Targa
    '97C4S (sold - and regretting it)

  8. #8
    Member
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    Aug 2020
    Location
    Shawnee, OK
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    95
    A combination of a failed air seal, temperature, altitude, humidity and cycling of these factors is the problem. The bad result is fogging, but a worse result is corrosion. Once the seal fails and temperature rises, air heats up and escapes the gage. When the temperature falls, outside air gets pulled into the gage and if the humidity is high, this air is full of water. When the temperature is below the dew point, then the moisture condenses, makes water droplets, thus fogging. When the gage heats back up, the fog can evaporate. This cycling continues with temperature, humidity and pressure changes which can either result in no fogging, intermittent fogging or at the extreme to the gage filling with water.

    This is a common problem for aero-space particularly in portions of the aircraft that are not pressurized. On critical components and military aircraft it is pretty common(and very expensive)to use a vacuum to coat the electronics and interior with paralene and use drain holes to solve this problem. On a less critical scale, the same problem occurs on double pane windows when the seal fails, then condensation starts showing up between the panes.

    Make sure the seals are good on the gages, live in the desert or a bag of desiccant if all else fails! If it is fogging, it will be corroding.

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