What kind of signal does tank level sensors transmit?

Discussion in 'OnBoard Electronics & Controls' started by Tharayman, Jun 15, 2021.

  1. Tharayman
    Joined: Dec 2020
    Posts: 11
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    Location: North cape

    Tharayman Junior Member

    My Faria oil pressure gauge has been acting up lately. The dial goes to max when it is powered, and does not move when the engine starts running. Instead of getting an expensive replacement I fel for temptation and got this cheap suclker instead ( 19.66US $ 28% OFF|4in1 lcd car digital gauge oil pressure gauge sensor 1/8 npt voltage fuel water temp meter M10 temperature sensors 10mm 12V 24V|Oil Pressure Gauges| - AliExpress https://www.aliexpress.com/item/4000935627983.html?spm=a2g0o.productlist.0.0.71dc5db82WqYRR&algo_pvid=cfb1ab15-3a22-4552-8346-a39d4e531c16&algo_exp_id=cfb1ab15-3a22-4552-8346-a39d4e531c16-0 )

    problem is the damn thing keeps sounding the alarm for empy tank. I do not have a tank level transmitter onboard, and they did not include one with the instrument. I will need to find som transmitter or fake one. There is a single white wire that is supposed to be connected to tank level sensor, so I guess it does not work by resistance. Perhaps by variying voltage like the oil pressure and temperature sensor?
  2. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Never hook a hot wire up to a sending unit. The sending unit measures resistance to ground.

    There is always an issue with matching sending units with Gauges. Most of the after market gauges are maybe 240 to 33 ohms ( I could be off here)
    Look at the back of the gauge or find out who makes it to determine what sending unit that it needs. The other subtlety is that you need to ensure that the order of the numbers. Ie some senders will give a 240 ohm reading, FULL, when the float is at the top and others will give you a 240 ohm reading when the float is at the bottom and might be called a 33 -240. Again the numbers could be wrong.

    Pertinent points
    1) Do not hook up a hot wire to a sender, boom!!
    2) Match the resistance of the sender to the gauge
  3. Tharayman
    Joined: Dec 2020
    Posts: 11
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    Location: North cape

    Tharayman Junior Member

    Did not go boom. Just got powered and resumed alarming.

    The gauge is as cheap as they come, and is in Chinese ;)
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The "Faria" gauges made in China are fake. They are totally worthless.
  5. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Barry is right but maybe this needs a little more explanation. The oil pressure gauge needs to be connected to a power source (usually 12 volt DC). A different wire is then run from the gauge to the sending unit on the engine. Usually the sending unit on an oil pressure gauge is grounded to the block that it's installed on. Fuel gauge senders will have a place to connect a ground wire that is connected to a grounding buss.

    As Barry said, the gauge measures the resistance generated by the sender. The reason you need power to the gauge is that you need a very small amount of power to make the needle move or an alarm sound or a bulb light up.

    Gonzo is probably right about the stuff coming out of China.


  6. Tharayman
    Joined: Dec 2020
    Posts: 11
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    Location: North cape

    Tharayman Junior Member

    How do I know if my Faria gauge is a Chinese knock off? I paid top dollar for it here in Norway about 3 years ago. Have tested it with two different oil pressure transmitters. One grounded to the engine, and one with a dedicated ground wire. The gauge still shows nothing.

    Guess I will have to find a 200 ohm resistor to connect to the aliexpress panel :)
  7. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell . . . _ _ _ . . . _ _ _

    "What kind of signal does tank level sensors transmit?"

    A partial signal, due to varying resistance .

  8. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    If you have a variable resistor, you can try it. Simply grounding the sensor wire should push gauge all the way over.
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