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  1. #1
    Join Date
    Jul 2009
    Location
    Missouri City, TX, USA
    Posts
    4

    Default "Hi I'm new to this forum.

    "Hi I'm new to this forum. I'm not a professional mechanic, however I've done nearly all my own mechanical work for over 49 years (starting with a gokart when I was 12), mostly on cars but also some boats (inboards, outboards, and I/Os), motorcycles, lawn mowers you name it and I may have fixed it.
    We took the boat out this past weekend, a 1974 Egg Harbor sportfisherman with twin 454 Crusader engines. A short ways into the trip a low oil pressure warning buzzer/light went on, however the oil pressure gauge at the helm was reading 40psi so we continued, shortly after that the engine shut down and wouldn't restart (the starter wouldn't crank). I crawled down next to the engine and jumped the starter at the solinoid and the starter cranked just fine, in addition after the intial restart from the solinoid we were once again able to crank the starter from the helm. Inspection of the oil pressure sender found 3 oil pressure senders. I disconected two so that only the sender that transmitted info to the oil pressure gauge still worked. We had no more problems after that. Am I correct in assuming that one of the sensors I disconnected was designed to shut the engine down and disable the starter if the buzzer/light was ignored for too long a period of time? BTW two of the sensors had a single wire and one had two wires going to it.
    Thanks for any insight you can give me about this issue.
    Steve"

  2. #2
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "This sounds like an electric

    "This sounds like an electric fuel pump is involved, correct? This also sounds like the engine is not a stock 1974, for sure.
    The twin connector switch maybe failed, turning off the fuel pump. Not allowing the starter to crank is usually only controlled by the neutral start switch. Either the engine was still in gear, or something else is going on.
    First question; what vintage motors?"

  3. #3
    Join Date
    Jul 2009
    Location
    Missouri City, TX, USA
    Posts
    4

    Default "Hi Dave, Thanks for your rep

    "Hi Dave,
    Thanks for your reply. Both engines have mechanical fuel pumps. The engine shut down while we were underway, possibly in the following confusion the operator (I wasn't at the helm, I was a passenger) forgot to shift the engine into neutral. However, the man at the helm was a professional captain who normally captained a wealthy oil mans 50 foot behemouth in an adjacent slip. I doubt that he would have forgotten to shift it into neutral. None-the-less I can't help but wonder what that two wire oil pressure switch is for.
    I don't know the history of the boat, it's a friends boat and he's mechanically challenged and has only owned it for four years. He took me out in it to help him figure out a bunch of mainly deferred maintenance type problems he's been having with it.
    I hope that helps
    Steve"

  4. #4
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,826

    Default "One of my old dock mates used

    "One of my old dock mates used the "fuel pump" style oil pressure switch (three lugs) to open the +12V to the ignition if there was a loss of pressure. Drawback, of course, was the extended cranking time to get it running.

    Those same switches can be used in the 'standard' warning horn set up, with a minor wiring mod. without seeing it, can do much more than speculate.

    The factory setup is the sender - big can, with the tapered end and the warning horn switch - usually a single stud."

  5. #5
    Join Date
    Oct 2007
    Location
    orlando, fl, usa
    Posts
    91

    Default To answer your question. the e

    To answer your question. the extra pot is to shut down the engine by grounding the coil. I had a 2 in one on mine and disconnected the extra one. This was not from the factory but most likely added by the engine installer. It will also prevent engine from starting until it has engough oil pressure.

  6. #6
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "After seeing so many defectiv

    "After seeing so many defective oil pressure switches over the years, I can't recommend ever relying on one to keep the engine running. Last year, I had one fail closed, turning on the horns during a mid gulf stream crossing, the actual pressure was fine. The idea of one doing that in a narrow channel and stopping the engine suddenly is not my idea of safety."

  7. #7
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    15,269

    Default "I had a similar but different

    "I had a similar but different situation. In my case (happened twice) the oil pressure alarm came on when there was nothing wrong with the motor--it was the ~*!^@ oil pressure switch. (And you wonder why I have high blood pressure!) Seems to be a common problem with marine engines for some reason.

    I agree completely that, having some dumb ass switch shut your motor down when IT wants to is a bad idea! We have oil pressure gages and a warning horn to let US make that decision.

    I'd eliminate that feature while making damn sure the oil pressure gage and alarm horn work properly.

    Jeff

    PS: Still a beginner, Steve! Got a few years on you."

  8. #8
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "Pressue tranducers (i.e.

    "Pressue tranducers (i.e. oil pressure switches) are a pretty common failure point in many engineered systems including marine gensets, well water systems, and of course, marine propulsion engines. You are much better off with an audible alarm backed up by a functional oil pressure gauge than a shutdown switch that may false trigger at a most inconvenient time."

  9. #9
    Join Date
    Jul 2009
    Location
    Fort Lauderdale, Florida, United States
    Posts
    6

    Default "5/6 miles off Freeport,Bahama

    "5/6 miles off Freeport,Bahamas, port engine shut down. When I looked in engine compartment,the bilge was full of oil. The plastic piece holding the wire conecctor popped out of the switch, sending oil into bilge. Glad I had the Switch. Might have saved an engine. Completed trip on one engine,removed the faulty switch, plugged the hole,replaced the oil and spent a few enjoyable days in the Bahamas.
    I keep an eye on oil pressure gage now."

  10. #10
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "JOe; I've had that happe

    "JOe; I've had that happen also, although that time, thankfully, was right off the coast and I had enough extra oil to get in. I've towed cars that had that defect too! For reasons like this, I've got alarms both on the tower and the lower station; although in your case, i'll bet the alarm did not sound. Scary..."

  11. #11
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,826

    Default Dave: Are you alarms indepe

    Dave:

    Are you alarms independent or dependent?

  12. #12
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "The visual/sonic alarm is ind

    "The visual/sonic alarm is independant from the gauge. But, i'll suppose if the entire plastic section flys off the metal sensor body, the alarm won't ring. That particular failure, I have not seen."

  13. #13
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,826

    Default "let me try again... did yo

    "let me try again...

    did you just run the 'upper' warning device to the "lower" device so, if activated, both would sound/illuminate?"

  14. #14
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "Ah, yes. The tower and lower

    "Ah, yes. The tower and lower station alarms are electrically in parallel. I have buzzers below and RS electronic sirens above."

  15. #15
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,826

    Default I haven't seen the insulat

    I haven't seen the insulator separate either....I was hoping you would have implemented that proven military strategy - dual redundancy - and was gonna share where that extra set of switches would fit cleanly.

  16. #16
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "I've seen mercruiser 7.4l

    "I've seen mercruiser 7.4l using two ports on the block, one for the switch, the other for the sendor. Mine just use the T fitting on one block tapped hole.
    I'm not too excited about doubling the number of those switches. I see more switches fail than oil systems fail. Plus, I can't really hear the bottom station buzzer from the tower at speed."

  17. #17
    Join Date
    Jul 2009
    Location
    Missouri City, TX, USA
    Posts
    4

    Default "I want to thank all y'all

    "I want to thank all y'all for your responses to my question. What I've recommended to my friend is to leave the warning buzzer and oil pressure gauge alone and disconnect the engine shut-off switch. I know that the pros and cons have been discussed and I tend to agree with diver dave, my friend does as well. Galveston Bay can get pretty busy and has many shallow areas, not the kind of place you want to risk having your engine shutdown due to a bad switch.
    Thanks again for confirming my suspicions about the oil pressure setup the engine has.
    Steve"

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