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Old 07-05-2020, 07:44 PM   #1
v8nut
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Default How do I test my oil pressure sender?

I am not seeing any oil pressure on the gauge on my 35 Phaeton. I don't think the oil pressure is zero. I assume the sender is a variable resistor and the gauge is an ammeter. I have a multimeter to measure the resistance. What readings should I expect? Or, should I test the gauge unit first? If so, how? Any advise would be appreciated. Jim in San Jose.
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Old 07-05-2020, 08:23 PM   #2
paul2748
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Default Re: How do I test my oil pressure sender?

You might want to consider purchasing a mechanical oil pressure gauge to check your gauge.
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Old 07-05-2020, 11:48 PM   #3
flatheadmurre
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Default Re: How do I test my oil pressure sender?

Air compressor...slowly raise the pressure to the sender and watch the gauge.
As already stated a mechanical gauge is way more accurate for checking what you actually have for oilpressure.
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Old 07-06-2020, 05:20 AM   #4
Don
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Default Re: How do I test my oil pressure sender?

The gauges all work on a pulse method,you cant check with ohm meter,better to get a manual to see how they work,I guess current draw would be how they work tho,!the sender has a bimetallic strip and points as does the receiver gauge,I do believe there is a slide wire res, the level arm moving up and down that determines the current draw which closes points on sender and makes gauge increase then points in gauge opens to stop ,it from moving,then process starts over again,,,,they senders can be repaired and adj very carefully,,better explained in a motor manual,,,
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Old 07-06-2020, 08:37 AM   #5
Scott52
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Default Re: How do I test my oil pressure sender?

I just went thru this on my 52. Engine is out of the car and I am installing a new harness. I wanted to make sure all the gauges worked with their senders before reinstalling the gauge cluster and harness under the dash. I tested all the gauges using the method from the shop manual which replaces the sending units with a 50 ohm variable resistor. All my gauges worked. I tested the oil sending unit with air pressure. Nothing. I connected the sending unit to the oil pressure line on my 48 Power Wagon, nothing. I bought a new sending unit and used the oil pressure from the Power Wagon and the new sender, old gauge worked fine. Bad sender. I was wondering if the sender was supposed to work with a 50 psi gauge and my gauge is 80 psi. I am in San Jose also. If the old gauge or the test setup is of value to you, PM me.
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Old 07-06-2020, 10:03 AM   #6
JSeery
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Default Re: How do I test my oil pressure sender?

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Quote:
Originally Posted by v8nut View Post
I am not seeing any oil pressure on the gauge on my 35 Phaeton. I don't think the oil pressure is zero. I assume the sender is a variable resistor and the gauge is an ammeter. I have a multimeter to measure the resistance. What readings should I expect? Or, should I test the gauge unit first? If so, how? Any advise would be appreciated. Jim in San Jose.
Your assumption would be incorrect. Modern sending unit work that way, but flathead era senders were current pulse devices. There is a heater coil in the sender and another one in the gauge. The pressure of the sender varies the current pulses which in turn varies the heat in the coils. The heater coil in the gauge heats a bi-metal strip which moves. This movement is what provides the needle movement.

I would not run the engine again until a mechanical oil pressure gauge is installed just to be sure. It is a good backup as well. I can be located in the glove box if more original dash appearance is an issue.
Attached Images
File Type: jpg Oil Pressure Sender.jpg (40.4 KB, 20 views)
File Type: jpg Oil Pressure gaugex.jpg (52.5 KB, 16 views)

Last edited by JSeery; 07-06-2020 at 10:13 AM.
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