oil pressure sending unit

[justinfonder]

i just bought my first jeep and the oil pressure gauge is not working. i tried a new gauge and still nothing. I want to replace the sending unit but i'm finding there are 2 options, 1 and 2 terminal. can anyone explain this to me, they look very similar to the untrained eye and i'm not sure which i need. i have an 81 CJ5 with a AMC 258 i6 / 4.2l . thanks guys

 

[Cheepjeep85]

take your old one off and match it up when you order it, or pick it up. you might get away with taking it off and cleaning it with a wire brush (threads and connections) the sensor grounds through the block if it doesn't have a good ground it will not work, over the years rust, oil, and general can build up in the threads.

 

[justinfonder]

good tip on cleaning. would save me 10 or 20 bucks too if i can make the old one work. will try it out as soon as i'm back in town

 

[MN CJ7]

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...............................................1 49-157
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.