Logo

Oil Pressure Sending Unit Ohms

390Express

Regular Contributor
How can I test the Ohms output from the oil pressure sending unit?

I tried grounding a multi meter, disconnecting the wire from it, and reading the post, but I did not get any discernible reading. Starboard gauge and sending unit works fine. I've ordered no less than three sending units for the port engine, all with different Ohm output ranges, and nothing... I purchased the first sending unit from W. Marine based off of the make/model (1996 Trojan Express, with Crusader 454XL TBI engines) - did not read right. Tried an AMZN sending unit that stated that it matched the gauge, nothing. Tried the VDO brand, VDO recommended sending unit for the gauge, nothing...

I would like to read the ohms of the stbd sending unit, so I know which sending unit to order for the port side.

I did verify the oil pressure for the Port engine with a mechanical gauge, so I know it's not the engine that is the problem.
 
are they single station units or double station units?

easiest way is to remove the sending unit and test it on a bench...using regulated compressed air and ohm meter.
0 PSI in should show at least 240 ohms
40 psi in should show 100 ohms
80 psi in should show 35 ohms, these are for a single station unit.
 
are they single station units or double station units?

easiest way is to remove the sending unit and test it on a bench...using regulated compressed air and ohm meter.
0 PSI in should show at least 240 ohms
40 psi in should show 100 ohms
80 psi in should show 35 ohms, these are for a single station unit.

Thanks Mako.

Am I understanding right, the sending unit needs no power source to get a measurable reading? I tried to test it while it was on the boat, and take an ohms reading off of the sending unit post that the gauge reeds from, but it was nearly impossible to get a discernable reading.

What is the best way to bench test? Put pressure to the input (NPT 1/8 threaded area), and put a pigtail on the post, ground at the base of the sending unit, and test the reading on the pigtail? That is what I am currently considering. Just have to make the setup... Sounds like I will need a screw-in shrader valve, and some NPT fittings, and a pressure gauge to get it done.
 
Thanks Mako.

Am I understanding right, the sending unit needs no power source to get a measurable reading? I tried to test it while it was on the boat, and take an ohms reading off of the sending unit post that the gauge reeds from, but it was nearly impossible to get a discernable reading.

What is the best way to bench test? Put pressure to the input (NPT 1/8 threaded area), and put a pigtail on the post, ground at the base of the sending unit, and test the reading on the pigtail? That is what I am currently considering. Just have to make the setup... Sounds like I will need a screw-in shrader valve, and some NPT fittings, and a pressure gauge to get it done.

Just clip one side of the ohm meter to the sender's case and the other lead to the threaded post. the pressure connection is what ever you have to the 1/8" NPT female to drive the sending unit, ideally with a pressure gauge somewhere in the line.

you can also test the gauge with three resistors, close in value to those cited above. With the resistor between the S and G terminals, apply power to the gauge. The 240 ohm resistor should show MIN value on the gauge, the 100 (110) ohm resistor mid-scale, and the 33 ohm resistor should show full scale. you can also test the sending wire by conning the resistor at the end of the wire (where the sending unit is).
 
Just clip one side of the ohm meter to the sender's case and the other lead to the threaded post. the pressure connection is what ever you have to the 1/8" NPT female to drive the sending unit, ideally with a pressure gauge somewhere in the line.

you can also test the gauge with three resistors, close in value to those cited above. With the resistor between the S and G terminals, apply power to the gauge. The 240 ohm resistor should show MIN value on the gauge, the 100 (110) ohm resistor mid-scale, and the 33 ohm resistor should show full scale. you can also test the sending wire by conning the resistor at the end of the wire (where the sending unit is).

Here's what I came up with for my bench test, just have to figure out if I need to ground this thing somehow, seems like it should work well. I can use the compressor air gauge to determine the pressure going to the sending unit, and read the ohms on the output side, hopefully... We'll see.
 

Attachments

  • IMG_8445.jpg
    IMG_8445.jpg
    75.1 KB · Views: 41
you don't need a 'ground' in the sense of an earth ground...just use the ohm meter between the case of the sender and the post...make sure the case connection point is 'clean'...you can use a small pair of vice grips if you're careful...
 
Just clip one side of the ohm meter to the sender's case and the other lead to the threaded post. the pressure connection is what ever you have to the 1/8" NPT female to drive the sending unit, ideally with a pressure gauge somewhere in the line. you can also test the gauge with three resistors, close in value to those cited above. With the resistor between the S and G terminals, free essays about advantages of technology explain the importance and real advantages of technology, the 100 (110) ohm resistor mid-scale, and the 33 ohm resistor should show full scale. you can also test the sending wire by conning the resistor at the end of the wire (where the sending unit is).
Sure thing! The instructions are talking about how to test an ohmmeter and a pressure gauge. To test the ohmmeter, you clip one side to a part of the circuit and the other side to a different part. To test the pressure gauge, you connect it to a part that measures pressure and ideally add a pressure gauge to check it. You can also test the gauge with three resistors, and check the wire by connecting a resistor to the end of it. The goal is to make sure everything is working correctly!
 
Back
Top