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1972 cutlass 350 water temp, and oil pressure sensors

1972 cutlass 350 water temp, and oil pressure sensors

Old November 20th, 2018, 06:04 PM
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1972 cutlass 350 water temp, and oil pressure sensors

Hi! So I got to wondering if the water temp, and oil pressure sensors on my 72 olds 350 that light up my idiot lights actually read pressures and temps other than the values that turn the idiot lights on or are they an on/off sensor? If they do actually read individual temps and pressures then are there guages and wires out there that would allow me to hook up directly to them without changing the sensors to mechanical ones?
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Old November 20th, 2018, 09:31 PM
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You have some good questions Chris. I'll try to relate how I understand them but may not answer all of them.

Most gauges and sender units will fall into two lines. Electric or mechanical. The proper gauge is needed with its corresponding sending unit regardless. So if you are buying a guage set you'll need the proper sending units for that gauge package. I would consider the factory set up as electric.

For example, the fuel gauge can be seen as an ohm meter that registers from O to 90 ohms full and empty and inbetween.

A voltage gauge/meter only needs a 12 volt signal. It will read what ever its getting from the source. That source could be from the alt. batt. or the fuse box or really anywhere else. Just under stand it will tell you voltage at the source. Voltage drop among wiring and might lead to reduced reading from where its recorded from.

An amp meter measures Current or the capacity of the alternators out put out at what ever rpm its being spun at. The caveat to understand is the high current has to go through the gauge. Volt meter does not need this.

If you're using an aftermarket mechanical oil gauge you don't need the factory sender. It use a capillary tubing to send the pressure signal to the gauge where the work is done. Same with the temp, a mech. gauge uses a capillary tube as the factory one uses an electrical signal. You can do both using a tee, that keeps the factory unit in conjunction with the after market one.

You can think of electric gauges as being on and off or digital but there is more to it than that. Usually a bimetallic spring is used to send a reading that is measured in ohms or a sweep of a needle.

Does that help, or does that muddy the waters pertaining your question?
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Old November 21st, 2018, 03:15 AM
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The sending units for idiot lights are simple on/off switches. I think the oil pressure is calibrated to provide a ground at about 7psi. The temp sender is calibrated to ground at around 248. Of the oil pressure is 8psi, or the temp is 247, the light stays off. Cars with the idiot lights have a extra green wire coming off the gauge connector (inside the wire harness) that goes to the ignition switch. The switch provides a ground when the key is turned past run, and before it gets to crank. That is a bulb test position, that wire should be disconnected if switching to factory style gauges. Hope that helps
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