Oil sending unit issues

Oil sending unit issues

Boneyard 79

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1979 CJ5 Renegade with original Levi interior: 258ci, 3 speed tran
Hey everyone, I'm looking for some guidance.

My oil pressure gauge was hovering around 20 at idle and while driving, never any higher. Then, it would suddenly drop like a rock to 0. Giving it some gas would "wake it up" back to 20.

I just replace the oil, the filter, and also replaced the sending unit with a Duralast. Now, I got nothing.....the gauge isn't moving at all. I crimped the wire with a needle nose around the new sending unit and still nothing.

Do I have a bad unit? Wrong part? What is my next step?

-Thanks
 
i would put a gauge with the correct thread size on where the oil pressure sensor goes and start the motor and monitor it
 
How long did you run it after you changed the oil? It sometimes takes a bit for the oil system to prime after you drain and change the oil.

Assuming you ran the engine for half a minute to a minute to give the pump enough time to prime, it's something else.

Double check to make sure nothing is blocking the sending unit. If you put teflon tape on, make sure you don't have any sticking out and plugging the hole in the sending unit.

Could be a bad sending unit. Could also be a loose wire somewhere between the sending unit and the gauge. Disconnect the wire from the sending unit, turn the key to "run" and check that you get voltage between the sending unit wire and the block. If not, that's your problem. Trace down the electrical connections to find where it's broken.

If you're getting good power to the sending unit, you either have a bad sending unit, bad gauge or you really do have no oil pressure. The best way to check that you really do have oil pressure is to install another gauge (either mechanical or an electrical with its own sending unit) and run the engine to see what happens. If the aftermarket gauge works, I'd say just use it to replace the factory gauge. If the aftermarket gauge shows no oil pressure, you need to figure that out.
 
I think I know what it is. I have the same problem. It's the connection on the oil sending unit. My CJ would also drop to 0 and sometimes jump up and down. The connector on the oil sending unit is press-on. I would push on it and it would be fine for a while. A week later it would hop back down to 0. I then replaced the press-on connector with a spade connector. The sending unit has a threaded screw for the connection so I just used a nut to secure the wire and I haven't had a problem with it since.
8216.jpg
You say you crimped the wire on with needle-nose but I'm still not sure that you have a good connection. Get out the multi-meter or re-do that connection with a crimp on connection like the one above.
 
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Great feedback,,,,much appreciated!
It will have to wait until next weekend before I can get back at it.
I'll give an update once I get it figured out.
 
Jeep CJ Oil Sending Unit and Gauge Information

The old Jeep Sender and Gauge parts and information is kinda messed up at this time. I went thru this about a year ago and some of the best info by "john" had a mix up in the revision and mixed up the resistance ranges and dates for the oil gauge & senders.

The older CJ's of the 70's use a 2" thick gauge and their own sender and resitance ranges. The newer Cj's have a 1" gauge and a different sender and resistanc range. Further the FSJ, full size jeeps, for these same years have yet another gauge and sender combo. So it is very easy to get the wrong suff and pair up the wrong stuff.

I wrote this up some time ago and could not find my notes in word on my hard drive so will have to put some of this together with my hand written notes and test information. I also spent $100 on oil senders to get this info too..... so hope this will save my fellow CJ owners some time and money and get their oil indication working.

The 1970's CJs use a 2" gauge
The sender to use is from NAPA #OP6657
Expensive little bugger and is $60, maybe you can get a discount, and if needed can also consider getting the Crown Gauge & Sender because the cost will be similar. I will give Crown info after the Napa Info.
I hooked this up to a presure regulator and gauge and ploted the pressure and resistance ranges using a multimeter.

Pressure............Measured............spec range CJ 1979 FSM
0-3 psi..... ..........239 ohms...........234-246 ohms
3-7......................239..................146-219
20...............................................149-157
40........................108..................100.5-105.5
80........................40....................32.5 - 34.5


Some time is the 1980's Jeep CJ went to a 1" thick gauge and the oil sender resistance ranges are different also. Crown does have a sender that will work, Crown #3212004 and sells for about $20. Morris 4x4.com was selling at 10% discount for a forum discount at the time so it cost me $19 and $4 to ship. Morris and Crown at that time list this for 1975 to 1986 for all CJ , Wagoneers and THIS IS NOT TRUE. THE CROWN SENDER WILL ONLY WORK WITH THE CJ NARROW 1" GAUGE.

This is what I measured with the Crown sender and a presure regulator, gauge, and multimeter.

Pressure............Measured............spec range
0-3 psi..... ..........70 ohms...........68-70 ohms
20........................33......................
40........................23..................21-25
60........................14....................
80.........................9....................7-13


FURTHER caution is the CJ and Full size use a different gauge and sender. I went thru about 15 years of Jeep Field Service Manuals and they do list the resistance ranges and have pics of the oil gauge face. The 1" and 2" gauges do have different faces. I would measure the oil sender pres/resistance range before installing any.

The Crown gauge is in the $20-30 range is I remember right. So it might be less expensive to get the CRown Gauge & Sender compaired to the $60 Napa sender needed for the 2" gauge. I have also been looking for a spair 2" CJ oil gauge and they are not easy to come by. Just thought I would mention this option as well.

TEMP SENDERS are also a issue. I purched 3-4 inexpensive units and the temp/reistance range was not correct. I ordered Napa's premium unit, double the price, and boiled it in water prior to install to test, can also be returned as new if does not pass test, and the boil waster is 212 Deg F or very close and will have a resistance value about 35 ohms. Take it out of boiling water FAST put on paper towel, something that is not a heat sink, and measure the resistanc with a multimeter. This needs to be done FAST you will see the resistance change in seconds. Thought I would throw this into the conversation.

My Temp gauge was bairly reading with PO set up. That temp sender and 3-4 more all failed till I tried the premium version. That one measured correctly.

I have seen the pressure and temp issues dozens of times.

Hope that helps.
 
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I've returned the duralast sending unit from auto zone and have the napa unit on order. In the meantime, I've placed the old unit in the engine block and the guage is back working (all over the place) I'll keep you all posted when the new one arrives.

Thanks again
 
Where can I get wires to connect the unit to the gauge? I just bought the original looking gauge from Morris and the premium sender from Napa but don't have the wires, any suggestions??
 
Where can I get wires to connect the unit to the gauge? I just bought the original looking gauge from Morris and the premium sender from Napa but don't have the wires, any suggestions??


Breezer,

From your post not sure if you are working on TEMP or Pressure..... The word "premium" leads me to guess you are working on TEMP... If you confirm I will try and help you along.
 
Where can I get wires to connect the unit to the gauge? I just bought the original looking gauge from Morris and the premium sender from Napa but don't have the wires, any suggestions??
At most automotive stores, hardware stores or Radio Shack. Be careful at Radio Shack. They sell some solid core wire but you want stranded core. One solid core of wire is more likely to break inside the insulation. With stranded core you can have a few strands break here and there without any loss of conductivity. Get about 14 or 16 gauge.
 
Where can I get wires to connect the unit to the gauge? I just bought the original looking gauge from Morris and the premium sender from Napa but don't have the wires, any suggestions??


Oil pressure sender not temp. What kind of wire do I need to ask for?


Sorry to say that combination the premium Napa oil sender and the Morris Gauge............. they have two different resistance/pressure ranges....


The Napa premium oil sender will not work with the Morris Oil Gauge



Need to read post #6 again and carefully. The resistance and pressure ranges are listed and what to get for the 70 CJs and the 80s CJs..

Std 18 AWG copper wire in a 19, 27 strand range or more will be fine. Get ring terminals to match the 18 awg range, with a #10 screw size hole or so, Blue Color Usually on Terminal.

The Napa sender is threaded and others may also be threaded. So a nut and few washers will work fine. That is what I have.
 
Re: Jeep CJ Oil Sending Unit and Gauge Information

Some time is the 1980's Jeep CJ went to a 1" thick gauge and the oil sender resistance ranges are different also. Crown does have a sender that will work, Crown #3212004 and sells for about $20. Morris 4x4.com was selling at 10% discount for a forum discount at the time so it cost me $19 and $4 to ship. Morris and Crown at that time list this for 1975 to 1986 for all CJ , Wagoneers and THIS IS NOT TRUE. THE CROWN SENDER WILL ONLY WORK WITH THE CJ NARROW 1" GAUGE.

This is what I measured with the Crown sender and a presure regulator, gauge, and multimeter.

Pressure............Measured............spec range
0-3 psi..... ..........70 ohms...........68-70 ohms
20........................33......................
40........................23..................21-25
60........................14....................
80.........................9....................7-13


FURTHER caution is the CJ and Full size use a different gauge and sender. I went thru about 15 years of Jeep Field Service Manuals and they do list the resistance ranges and have pics of the oil gauge face. The 1" and 2" gauges do have different faces. I would measure the oil sender pres/resistance range before installing any.

The Crown gauge is in the $20-30 range is I remember right. So it might be less expensive to get the CRown Gauge & Sender compaired to the $60 Napa sender needed for the 2" gauge. I have also been looking for a spair 2" CJ oil gauge and they are not easy to come by. Just thought I would mention this option as well.

Hope that helps.

This thread, my post #6

Measured...... what the sender out put was as "measured" by me

Spec Range...... is from the Jeep Field Service Manuals in gauge section
 
Re: Jeep CJ Oil Sending Unit and Gauge Information

I got everything but no readings. Do I need to connect the positive side of the gauge to the negative on the coil?
 
Re: Jeep CJ Oil Sending Unit and Gauge Information

The only thing that connects to the - side of the coil is the tach and the ignition module.

The oil pressure sending unit output connects to the oil pressure gauge - terminal.

The only thing that connects to the - side of the coil is the tach and the ignition module.

The oil pressure sending unit output connects to the oil pressure gauge - terminal.
 
Re: Jeep CJ Oil Sending Unit and Gauge Information

I did that but no reading. The light stopped working when I connected it as well
 
Re: Jeep CJ Oil Sending Unit and Gauge Information

Would love to talk to you sometime. Call me at 2059362763. Best time is after 8 central. I have a ton of questions!!
 
Re: Jeep CJ Oil Sending Unit and Gauge Information

I am having the same exact issue. I checked the output on the oil pressure sender and it was at 93 until the engine warmed up and it was 0. I read earlier in this post to check the voltage on the line to the sender. I have just over 5vdc, should it be 12?
 

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