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  1. #1

    Default Temp gauge on 454 is bouncy

    This is likely my sending unit right??? Thought maybe some other diagnostics might be in order. Here's the deal...twin 1986 454's FWC. The temp gauge on my last trip had a mind of its own. Port engine holds steady at 150-degrees regardless of rpm setting. However Stbd...holds 150-degrees at 2000 rpms but at 2500 starts bouncing between 140-160 degrees. at 3000 rpms it bounces around 130??? I have both upper and lower helm gauges (34 Tolly Sports Sedan) and the reading is the same at both stations. Could it be anything other than sending unit? Should I run a continuity check on the wiring? As always....appreciate the expert advice.

  2. #2
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,473

    Default Re: Temp gauge on 454 is bouncy

    If you have a selection of resistors around, you could sub the sender with a 100 and then a 220 ohm resistor to simulate the sender. My $ would be on the sender. Be aware the dual station senders are different than single station.

  3. #3

    Default Re: Temp gauge on 454 is bouncy

    I could swap sending units between the two engines to clearly identify that its the SU right? My concern is how and what do I test if the SU turns out to be okay? And why would the engine RPM have an affect...unless its strictly vibration. I checked all connections...which show no corresion and are on tight.

  4. #4
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,473

    Default Re: Temp gauge on 454 is bouncy

    Wild guess is the engine vibration modifies the sensor behavior. I think they are made with an internal "leaf spring" type connection to the top stud. A little internal corrosion might cause this.

  5. #5
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,617

    Default Re: Temp gauge on 454 is bouncy

    With dual station senders, the "resistor" substitutes should be have the single sender values: 120 ohm should show the min mark, 56 ohms half value, 16 ohms, full scale. Lots of people skip the resistors and the 50% test and just jump the lead at the sender to ground and look for full scale (plus).

    DD's guess on the sender sounds plausible to me....another thing to do is get an IR gun and check the t-stat housing. If that's constant, change the sender and make sure you get the dual station flavor.

    I'd be inclined to switch wires between the gauges and the sending units vs switching the sending units (don't have to worry about two coolant system purgings). You can probably do this easily at the lower helm where the harness connects to the instrument panel.

  6. #6
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,473

    Default Re: Temp gauge on 454 is bouncy

    TEMP #334AD

    100deg F 412ohm
    145 230
    190 137
    235 85.9
    280 56

    For those interested, here are the SINGLE station equiv. values for a Stewart Warner temp sender.

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