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Oil Sending Unit, testing
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Atlantis
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PostPosted: Thu May 28, 2009 12:06 pm    Post subject: Oil Sending Unit, testing Reply with quote

The VW manual does not have any testing info for this so what is it suppose to read on the sending unit for the oil light?

Electrical....ripping my hair out, moving to peeling the skin soon. Sad
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PostPosted: Thu May 28, 2009 12:15 pm    Post subject: Reply with quote

I believe the OIL PRESSURE LIGHT switch is supposed to show a short below 7 psi. That is a common number in oil protection circuits. That assumes 10 psi oil pressure per 1000 rpm, so an idle of 700 RPM should give you at least 7 psi. Below that would be bad so the light would come on. Grounding the circuit at the sender should make the light on the dash come on. If you have an OIL PRESSURE GAUGE, you would need resistance numbers from the manufacture to test. Some VDO aftermarket senders come on at 9 - 10 psi so you may get an oil light flicker on a hot day at a slow idle and still be safe.
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Atlantis
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PostPosted: Thu May 28, 2009 4:05 pm    Post subject: Reply with quote

Let me rephrase, what does the sender test at on a multimeter. I did ground the wire and the light came on. I want to see if the sending unit for the oil light is working correctly. What is it suppose to test at. Thanks

SGKent, still good knowledge I appreciate it.
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Randy in Maine
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PostPosted: Thu May 28, 2009 4:12 pm    Post subject: Reply with quote

With the engine off but the key in the "on" position, remove the wire to the sender. Light should go off. Touch the wire to a ground (the engine is the ground) the light should come on.

That is the test. The end.
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PostPosted: Thu May 28, 2009 4:14 pm    Post subject: Reply with quote

Atlantis wrote:
Let me rephrase, what does the sender test at on a multimeter. I did ground the wire and the light came on. I want to see if the sending unit for the oil light is working correctly. What is it suppose to test at. Thanks

SGKent, still good knowledge I appreciate it.


-7 lbs= 0 ohms
+7 lbs=infinite ohms

How's that? Wink
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Atlantis
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PostPosted: Thu May 28, 2009 6:49 pm    Post subject: Reply with quote

Randy in Maine wrote:
With the engine off but the key in the "on" position, remove the wire to the sender. Light should go off. Touch the wire to a ground (the engine is the ground) the light should come on.

That is the test. The end.


This does not test the sending unit itself.
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Atlantis
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PostPosted: Thu May 28, 2009 6:50 pm    Post subject: Reply with quote

busdaddy wrote:
Atlantis wrote:
Let me rephrase, what does the sender test at on a multimeter. I did ground the wire and the light came on. I want to see if the sending unit for the oil light is working correctly. What is it suppose to test at. Thanks

SGKent, still good knowledge I appreciate it.


-7 lbs= 0 ohms
+7 lbs=infinite ohms

How's that? Wink


what?
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busdaddy
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PostPosted: Thu May 28, 2009 8:14 pm    Post subject: Reply with quote

Atlantis wrote:
busdaddy wrote:
Atlantis wrote:
Let me rephrase, what does the sender test at on a multimeter. I did ground the wire and the light came on. I want to see if the sending unit for the oil light is working correctly. What is it suppose to test at. Thanks

SGKent, still good knowledge I appreciate it.


-7 lbs= 0 ohms
+7 lbs=infinite ohms

How's that? Wink


what?


Ummmm........ maybe you should jusy buy a new one.
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PostPosted: Thu May 28, 2009 8:54 pm    Post subject: Reply with quote

busdaddy wrote:
Atlantis wrote:
busdaddy wrote:
Atlantis wrote:
Let me rephrase, what does the sender test at on a multimeter. I did ground the wire and the light came on. I want to see if the sending unit for the oil light is working correctly. What is it suppose to test at. Thanks

SGKent, still good knowledge I appreciate it.


-7 lbs= 0 ohms
+7 lbs=infinite ohms

How's that? Wink


what?


Ummmm........ maybe you should jusy buy a new one.


I like to test things before deeming them junk. If I would have not had this mentality I would have ended up junking half of the shit on this bus that I got working.
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busdaddy
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PostPosted: Thu May 28, 2009 10:04 pm    Post subject: Reply with quote

Atlantis wrote:
busdaddy wrote:
Atlantis wrote:
busdaddy wrote:
Atlantis wrote:
Let me rephrase, what does the sender test at on a multimeter. I did ground the wire and the light came on. I want to see if the sending unit for the oil light is working correctly. What is it suppose to test at. Thanks

SGKent, still good knowledge I appreciate it.


-7 lbs= 0 ohms
+7 lbs=infinite ohms

How's that? Wink


what?


Ummmm........ maybe you should jusy buy a new one.


I like to test things before deeming them junk. If I would have not had this mentality I would have ended up junking half of the shit on this bus that I got working.

Well with the engine off and less than 7 lbs of oil pressure the terminal should be grounded to the body of the sender, when the oil pressure is above 7 lbs the circuit opens, there is no in between, it's a simple switch, on or off.
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Randy in Maine
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PostPosted: Fri May 29, 2009 4:30 am    Post subject: Reply with quote

Or perhaps hooking up a T with a mechanical gauge on one side and the OP sending unit on the other. Then you could confirm the "light on" oil pressure.

Usually they just leak oil and get replaced.


Last edited by Randy in Maine on Fri May 29, 2009 4:38 am; edited 1 time in total
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PostPosted: Fri May 29, 2009 4:35 am    Post subject: Reply with quote

Atlantis wrote:

I like to test things before deeming them junk. If I would have not had this mentality I would have ended up junking half of the shit on this bus that I got working.


I totally support this mentality, but on the otherhand, the oil sending unit is maybe the most important thing to have working, and they're cheap...

Randy's got the trick though - Tee it with an OP gauge and see if the ohms change at 7psi...
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PostPosted: Fri May 29, 2009 5:23 am    Post subject: Reply with quote

I'm interested to know why you need to test it. Is your oil warning light staying on while the engine is running? It's obviously not leaking or you'd have replaced it. If your light IS staying on, then are you sure your timing and idle are adjusted correctly? Too low an idle and it will stay on or pulsate. I just replaced mine with a Duralast unit from Autobone. It works great and was only $4. A continuity/ohm tester and some manuvering with an air compressor will allow you to test yours. From the blade connector to the threads should be a closed circuit. Then set your regulator to 10psi and pressurize the sender. Voila, open circuit!
Or spend $4 and know real quick if it's rebuild time. Peace!
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PostPosted: Fri May 29, 2009 6:30 am    Post subject: Reply with quote

Quit screwing with ohms...and simply set your meter to "continuity"....meaning on/off...contact or not. You can thread this into a piece of pipe made of cheap tee's from homey depot and pump it up with a hand pump or bicycle pump. Keep the test rig you can use it again.

Buzzer on the VOM will be on.... with no pressure on the switch (this makes the ground contact for the idiot light)......when the buzzer on the VOM turns off as you add pressure....check gauge readings. Testing done. Ray
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PostPosted: Fri May 29, 2009 7:08 am    Post subject: Reply with quote

Ok sweet thanks to all.


I am redoing the electrical in the bus. It is a massive mess. I am almost done. The oil light and fuel gauge are the only things left to figure out.

The oil light was working and then not working, then working and now not working. I took the wire off the sending unit and grounded it to the engine and it worked. So everything from the light bulb and wiring all the way back to the sending unit works. So I wanted to test the sending unit itself.
My oil pressure is fine, the engine runs delicious. I will probably replace the oil pressure sending unit with something nicer anyway. I just want her out on the road with 100 percent perfect electrical.
I also will be installing a temp gauge and oil pressure gauge anyhow. I am soldering and heat shrinking every wire in the harness as well.


Thanks to all!
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PostPosted: Wed Dec 01, 2021 9:59 pm    Post subject: Re: Oil Sending Unit, testing Reply with quote

I was told today by a gentleman who's helping me fix some wiring in my bus that to troubleshoot th sending unit, "take it out of the block and ground it hard to frame/ground/battery negative, whatever.  With the key on and engine off, the light should come on (DO NOT start the engine with unit out!!!).  If not, it's the sending unit.  If it DOES come on, put it back in the block and turn the ignition on and see that the light turns on again.  Then crank the engine and the light should go out, indicating oil pressure"
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Last edited by CheapBusForSale on Thu Dec 02, 2021 10:54 am; edited 1 time in total
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PostPosted: Wed Dec 01, 2021 10:04 pm    Post subject: Re: Oil Sending Unit, testing Reply with quote

Light comes on when in the on position

when bus starts oil pressure builds and light should go out

If light never comes on, you can remove the wire from the sender in the on position and ground it, it should come on. If not then the circuit or light bulb, or fuse is bad.

If the light never goes out when the engine is on, the only way to easily test it is to replace it, or use a mechanical gauge to see if you have pressure.

DON"T leave the key in the on position for long so not to damage the ignition system (coil, points, electronic ignition etc)
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PostPosted: Thu Dec 02, 2021 10:37 pm    Post subject: Re: Oil Sending Unit, testing Reply with quote

Method for fixture testing VW oil pressure sending units of all kinds:

- procure a 1-1/2" length of 1'' aluminum round stock.
- drill a pilot hole for a m10-1 metric tap all the way through the center. Use a drill press or, if you have access to one, a lathe. Tap half way through with a m10-1 tap.
- drill a pilot hole for a 1/4" pipe tap half way through the other side. Tap it half way through with a 1/4" pipe tap.
- Screw in a short 1/4"pipe nipple, followed by a 1/4" pipe "T", followed by a suitable male air hose coupling. Screw a 100 psi 1/4" pipe thread pressure gauge into the remaining "T" opening.

To use:
- screw the pressure switch / sender into the fixture m10-1 end.
- connect the fixture to a source of variable pressure shop air.
- connect an ohmmeter between the sender and the fixture.
For a switch:
- increase air pressure until the switch closes. Make a note of the pressure.
- decrease the pressure until the switch opens. Note the pressure.
For a pressure sensor:
- increase pressure and record resistance readings for pressures from zero to 80 psi, in 5 psi increments. Compare to the sensor spec, or to another sensor.
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PostPosted: Fri Dec 03, 2021 1:41 pm    Post subject: Re: Oil Sending Unit, testing Reply with quote

And even if you decide to go for a separate oil pressure transducer that feeds a pressure reading to the dash, it is a good idea to use a T piece to allow you to continue to use the original simple foolproof sender and dash light combination.

1. Because the combined senders switch the oil warning light on at a higher pressure than the stock sender.

2. Because if you rely only on a gauge to show pressure, you do not get the warning light.

(I have an electronic sender rated to 250F .. one day I got my engine really hot, I think the thermostat rod jammed, and the oil pressure dropped .
The electronic sender told me the pressure was negative, even though the warning light was only just flickering via the stock switch. In normal use with that sender, 0psi is 0.5 volts, and 100psi is 4.5 volts .. but when its hot the output goes under 0.5 volts .. )
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PostPosted: Fri Dec 03, 2021 1:54 pm    Post subject: Re: Oil Sending Unit, testing Reply with quote

I love telford’s answer because that’s what you need to do if you wanna test the switch - and it’s why no one bothers to test the switch. It’s a simple on/off switch. No real way to test it unless you have some method of applying a pressurized liquid into the port on the switch.

No pressure = switch closed = oil light on.
Pressure = switch open = oil light off.

Kinda the same principle as the brake light switches, just opposite.
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