1968 300, any way to have engine temp lights AND a gauge?

Engine, Transmission & Driveline

  1. WissaMan

    WissaMan Well-Known Member FCBO Gold Member

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    I kind of like the "Cold" and "Hot" idiot likes on my 68 Chrysler. But I also want a temperature gauge. Is there any way I can have my cake and eat it too?
     
  2. commando1

    commando1 One Sick Puppy FCBO Gold Member

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    You can add another sending unit and mount an aftermarket guage under the dash


    It's that simple.
     
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  3. haywire 440

    haywire 440 Well-Known Member FCBO Gold Member

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    There is a second hole by the idiot light sending unit to place another temperature gauge sending unit on the front of the engine.
     
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  4. WissaMan

    WissaMan Well-Known Member FCBO Gold Member

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    Really? I didn't realize -- that's cool. I knew there was a second hole for the oil pressure but not for the water. Thanks!
     
  5. Ripinator

    Ripinator Old Man with a Hat

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    Yes. Its a little pipe plug similar to the plug used for the oil pressure sender you use for an oil pressure gauge. Its smaller.
     
  6. Yeahrightgreer

    Yeahrightgreer Senior Member

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    What temperatures do the idiot lights actually engage at? I’ve always assumed if it got to the point where the hot light came on - you’re screwed anyway.
     
  7. Ripinator

    Ripinator Old Man with a Hat

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    I don't know. . . Its most likely the temperature where 50/50 anti-freeze coolant boils. If you shut her down when you see the light, yer probably OK.
     
  8. Snotty

    Snotty Senior Member FCBO Gold Member

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    Just be aware of one thing: right now, with just idiot lights, you will drive your car and enjoy it, without any thought to the heat in the motor as long as the red one is not lit. But, once you install the gauge, you will always be aware of the temp and wondering if you're too hot. It's a great way to destroy a nice drive.

    Just my opinion....
     
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  9. live4theking

    live4theking Old Man with a Hat

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    The second plug you're looking for is on the front of the engine below where the factory sender is located.
     
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  10. jct

    jct Senior Member

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    This is what you are looking for 20180630_133535.jpg
     
    Last edited: Nov 1, 2018
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  11. WissaMan

    WissaMan Well-Known Member FCBO Gold Member

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    JCT, which thing should I be looking at? The short unpainted thing or the long unpainted thing?
     
  12. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Those are the nipples for the heater hose.

    Use the plugged hole circled.

    water pump.jpg
     
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  13. Trace 300 Hurst

    Trace 300 Hurst Professional Tinkerer FCBO Gold Member

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    This is a fantastic post, as I was just considering doing the same thing. The PO installed a decent "Day Two" underdash three-gage pod using the normal sending unit location for his gage, and it works good. But I'd like to have the groovy Cool and Hot lights, too. I'm thrilled to learn that there's another hole available, as I was thinking of using the similar block drain plug hole(s) or making a fitting and tapping into the heater hose.
     
    Last edited: Nov 1, 2018
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  14. WissaMan

    WissaMan Well-Known Member FCBO Gold Member

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    Cool, thanks everyone for the detailed info!
     
  15. CBODY67

    CBODY67 Old Man with a Hat

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    Here's an idea . . .
    Get a "heat gun" and use it to check the temperature at the thermostat housing as the "COLD" light goes out. Probably in the neighborhood of 175 degrees F or so? The "HOT" light will probably trigger at about 240 degrees F, which is a bit under the boing point of a 50/50 coolant mixture with a 15lb radiator cap (which I believe is 260 degrees F or so?).

    By observations going back into the middle '60s on our '66 Newport and other similar factory a/c Chryslers (and from techs who worked on them), if the factory cooling system is clean and has a good radiator cap, you'll never see the "HOT" light illuminate unless . . . there is a leak and part of the coolant has leaked out, a failing water pump, a failed thermostat, or a failed fan clutch. Now that the cars are now much older, these "HOT" modes might also include a cooing system with a lot of "accumulation" in the water jackets that needs new freeze plugs and a good flush when they are removed for replacement.

    A more "normal" time to see the "HOT" light would be after a restart in the summer HOT weather, momentarily when the engine starts after sitting a while after driving. It should go out as soon as the engine has run a minute or less, typically.

    As noted, it's pretty easy to add a temp sensor for an accessory gauge. There are always advantages to having a gauge to monitor, but if everything's in good working order, the lights can do just fine.

    Enjoy!
    CBODY67
     
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  16. commando1

    commando1 One Sick Puppy FCBO Gold Member

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    It's in the FSM on what temperatures turns off the COLD light.
    I can't recall if the FSM states specifically when the HOT light comes on.
     
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  17. Barry S

    Barry S Member FCBO Gold Member

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    Great post, thanks for the info, and especially the pics! I had some overheating issues over the summer - the hot light came on when I pulled off the interstate to get gas when I was returning from the Mopar Nationals in Columbus. The light went off when I revved up the engine so it seemed like it was a problem with coolant flow. I've flushed everything and things seem to be better (no hot light) but I'd like to know the temp to get a better feel for how the cooling system is working. That's on my list in the spring when the Newport comes out of storage.
     
  18. Snotty

    Snotty Senior Member FCBO Gold Member

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    There it is! My "Hot" light did come on in my Newport.

    My son and I had driven to the "American Graffiti" show in Modesto in 2007. It was a warm day driving home so I put the top up and turned the AC on. About an hour from Bakersfield it came on. I turned off the AC and it went off. About 15 minutes later I turned it back on and everything repeated. Once I made it to the Bake the hot light stayed on, even with the AC off. The next weekend I pulled the radiator and had a third row added to it. Have never had the problem again.

    American Grafitti Show, Modesto, 2007. If you've never been, it's a great show!
    IMG_2009.JPG
     
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  19. Larry Jett

    Larry Jett New Member

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  20. Larry Jett

    Larry Jett New Member

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    Indeed, you can buy a Dakota Digital guage that has the input screwed into those extra holes mentioned and it fits very nicely into the ash tray in my 1966 300. Since the ashtray isn't used any more you can just leave it shut unless you are concerned. It is very accurate and you can quickly learn how much speed, load, altitude and outside temp affects the engine temp.
    Reach out to larrywjett@gmail.com if you want photos and details. I have put the guage in every Mopar I ever had because it is spot on correct. No need to add stuff under the dash.
     
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