1. carguy300

    carguy300 New Member

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    Can my oil pressure switch fail without leak? I just cranked up my 300 awhile ago, oil light did not go off. Tried 3-4 times only short time, no luck. Oil level good, new oil, Amsoil 10/40. never had this prob before. Lifters, rockers All quiet. Ideas?
     
  2. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Yes, there is a rubber diaphragm inside the sending unit. As the diaphragm ages, the rubber gets hard and sometimes can not move enough to open the switch for the idiot light so that the light will stay on. An internal leak inside the sending unit can also fill the back side of the diaphragm with oil causing the same result. It would probably be a good idea to hook up a mechanical gauge in place of the sending unit to verify that you have oil pressure before proceeding further as a failing timing chain can clog the pick up screen and cause a zero or very low pressure scenario, as can a broken rocker or push rod that has caused the lifter to exit its bore in the block.

    Dave
     
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  3. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    AS a follow up, a short in the lead to the sender can also cause the idiot light to stay on. Test for this by unplugging the lead, if the light stays on after it the lead is disconnected, you have a short.

    Dave
     
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  4. 71Polara383

    71Polara383 Kid with ballcap FCBO Gold Member

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    Yep had a sender go bad on my 71. Oil light stayed on. Quick, cheap, easy fix!
     
  5. carguy300

    carguy300 New Member

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    Thanks Dave. I will ck for pressure at the sending unit, we had 2 or 3 days in low 30's last week, thought it might have helped with issue. Since ive had it, over a year the light has always gone off 3-5 seconds.
     
  6. carguy300

    carguy300 New Member

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    I am hoping thats all it is!
     
  7. 71Polara383

    71Polara383 Kid with ballcap FCBO Gold Member

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    That can do it too. Thicker oil, colder temperature, harder to move to the top of the engine.
     
  8. CBODY67

    CBODY67 Senior Member

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    Back in the middle '70s, when STP came out with their "double filter" oil filter, I got one for the '66 Newport. Had been using normal Motorcraft FL-1A filters with no issues, but wanted "something better" (allegedly), so I got one.

    At the next oil/filter change, we put it on. When I started the car, the oil light did not go out as it had been doing, but stayed on. No additional engine noises, just that the oil light would not go out. After a few minutes of that, it came off and a new FL-1A went back on. Oil light went out immediately, as it had been doing.

    The suspicion was that the added filtration in the STP filter was a "resistance to flow", allowing some through, but not enough to turn the light off. Therefore, I might inquire as to what oil filter is on the engine?

    At the time, the car had over 100K on the engine AND accumulated about 50K more afterward, when I got the '70 Monaco Brougham "N" as my daily car. The Newport began to lead a sheltered life under the carport.

    Just some thoughts,
    CBODY67
     
  9. mikedrini

    mikedrini Active Member FCBO Gold Member

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    I doubt this is the issue, but just chiming in, mine was a wiring issue where the connector was loose.
     
    Last edited: Nov 6, 2019
  10. carguy300

    carguy300 New Member

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    I have verified not a wire/ short problem. I am using a Napa Gold( WIX) oil filter. I changed the oil a few months ago and light op was ok than. Going to replace pressure this afternoon, hopefully that will cure it.
     
  11. carguy300

    carguy300 New Member

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    Thanks for all the info guys. I replaced pressure switch awhile ago and oil light went off in about 3 seconds. Oils well that ends well! Thanks again.
     
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