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Technical Murphy safety switch question

Discussion in 'Traditional Hot Rods' started by birdman1, Feb 7, 2020.

  1. birdman1
    Joined: Dec 6, 2012
    Posts: 994

    birdman1

    I have a Murphy oil guage that is also a low oil pressure switch that will kill the em=ngine if the oil pressure drops to a preset level. Does anyone know if it is adjustable? It reads from0-75 pounds, but there is a solid line on the display at 15 and 30. i have never taken one apart to see how it works, thought maybe one of you have. thanks. DSC_0036.JPG
     
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  2. Wanderlust
    Joined: Oct 27, 2019
    Posts: 168

    Wanderlust

    Small Allen key will move the indicator needle, gauge needs to be wired into your ignition
     
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  3. Yup ^^^^^^

    I really never saw the need for one in your private vehicle, fleet cars and trucks yes. Most people watch their personal vehicle a little closer than that. If it were mine I would probably set it in the dash and not wire the safety part in at all and let it be a conversation piece. ;)
     
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  4. weps
    Joined: Aug 1, 2008
    Posts: 531

    weps
    Member
    from auburn,IN

    Neat piece
     
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  5. Doublepumper
    Joined: Jun 26, 2016
    Posts: 654

    Doublepumper
    Member

    I've wired up many Murphy safety switches over the years and can say if you do decide to wire it up for use it would be best to use it to energize a small indicator light or energize/de-energize a relay only. The switch contacts aren't stout enough for any heavy current flow through them and will burn up over time.
     
  6. hotrodjack33
    Joined: Aug 19, 2019
    Posts: 1,120

    hotrodjack33
    ALLIANCE MEMBER

    Sounds like a bad idea on a your "street" car. Starting would require cranking it long enough to get the oil pressure up high enough to start.
    Or, hot summer day (oil a little thin) stop at a red light, get a little crud in the carb and RPMs drop too low...dead in the street.:(
     
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  7. borderboy1971
    Joined: Oct 20, 2008
    Posts: 705

    borderboy1971
    Member
    from Canada

    I can't speak for how that gauge switch is wired, but if it simply grounds the circuit when pressure drops, you shouldn't run that directly with electronic ignition or you will fry the module. It can still be used by using a relay involved though. Be aware of this though.
    Also keep in mind that 10 psi per 1000rpm for RACING engines is all that's needed.
     
    Last edited: Feb 7, 2020
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  8. Murphy32
    Joined: Oct 17, 2007
    Posts: 726

    Murphy32
    ALLIANCE MEMBER
    from Minnesota

    Be aware...this gauge operates on the principles of "Murphy's Law"-
     
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  9. BJR
    Joined: Mar 11, 2005
    Posts: 6,517

    BJR
    Member

    So if it grounds your ignition with zero oil pressure, how do you start the car? Crank it until you have enough oil pressure to make the gauge not ground the ignition?
     
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  10. 500caddy
    Joined: Feb 8, 2019
    Posts: 89

    500caddy

    You put in a push button switch you press until you have oil pressure we had them on combines


    Sent from my iPhone using The H.A.M.B. mobile app
     
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  11. BJR
    Joined: Mar 11, 2005
    Posts: 6,517

    BJR
    Member

    Makes sense thanks.
     
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  12. nochop
    Joined: Nov 13, 2005
    Posts: 1,720

    nochop
    Member
    from norcal

    Maybe on a pump motor or industrial engine that runs on automatic without direct observation
     
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  13. lippy
    Joined: Sep 27, 2006
    Posts: 4,973

    lippy
    Member
    from Ks

    Also irrigation engines. So if you left it running and forgot to check the oil level (Happens if you have 35 irrigation systems to take care of) low oil pressure would shut it down. Lippy
     
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  14. birdman1
    Joined: Dec 6, 2012
    Posts: 994

    birdman1

    It was installed on a 1955 tbird I bought last year. I am still using it in it, but not the kill wire. Thanks
     
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  15. Budget36
    Joined: Nov 29, 2014
    Posts: 4,228

    Budget36
    Member

    I'd guess it would be wired into the run side, I/e like bypassing a ballast resistor when cranking? Just my thought.
     
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  16. BJR
    Joined: Mar 11, 2005
    Posts: 6,517

    BJR
    Member

    That makes even more sense. Thanks for the post.
     
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  17. rinnda
    Joined: Dec 9, 2019
    Posts: 1

    rinnda

    Hi, you got a good point!!
    Some people do not switch on the ignition before they achieved a certain oil pressure by just cranking the engine with the starter. It takes some turns and you got it up to 20-30 or so. This could be made automatically by this gauge. Good deal, isnt it?

    In the other hand i do see the issue that If you lose oil pressure unfortunately in a situation like passing an other car it could be fatal to lose the spark in that moment. I would better have switched on just a buzzer in that moment. It gives me the decision to stop the engine as soon asbl I can. I think an engine does not get killed within 10sec with no oil pressure. But you survive...
     
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  18. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,973

    sunbeam
    Member

    Most comerical apps have an over ride push button that you hold until you get oil pressure. It will also let you run the vehicle to get it out of harms way.
     
    Last edited: Feb 9, 2020
  19. nochop
    Joined: Nov 13, 2005
    Posts: 1,720

    nochop
    Member
    from norcal

    Looks something that would add to the “ why won’t this bit*h start now”....
     
  20. Ford Pintos had a low oil pressure switch. You may note that Ford no longer uses one, it was a failed experiment. LOL
     
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  21. dwollam
    Joined: Oct 22, 2012
    Posts: 1,127

    dwollam
    Member

    We have to run an oil pressure switch on my son's O/T mini truck dirt circle racer because we run an electric fuel pump. Pump is wired thru the pressure switch. It is in case one ends up upside down, it kills the fuel pump when oil pressure drops so ya don't pump gas on a possible fire. We have found that if it sets a long time, like over the winter, that we have to pull the connector off and bridge across the terminals to make the fuel pump run. Some of the guys run a momentary switch to bypass it like someone said earlier.

    Dave
     
  22. birdman1
    Joined: Dec 6, 2012
    Posts: 994

    birdman1

    i worked at a Ford dealer in the early 80's, seems like some crown vic's had then for a while?
     

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