Oil & Temperature Gauges need the correct sensors to work... part #s, info and tests
I just got my 78
CJ7 AMC 304 running after replacing the motorcraft carb and as the engine warms up the oil pressure drops. When i first get it cranked the gauge reads around 18-20psi and when the temp gauge gets to about 1/4 hot the pressure gauge drops to zero and it starts to smoke more than the usuall. Do you guys have any ideas or suggestions?
Hi,
I have a 78 CJ and had some fun / NOT trying to get my temp and press gauge to indicate and operate correctly had some very interesting turns... This comes up often.... but suprised its not every day but it does come up 2-5 times per month.
GOOD BACKROUND INFO.... always to put all the background info you can. When looking at oil pressure....... how many miles, has there been a rebuild and is ANYTHING in question with the engine rebuild. What oil specs and brand, what are your outside/air temps, what are the miles on engine. EX a motor with 200k will not have the same pressure as 50k usually. So tell us more....
The good news possible.... both the Oil Pres and Water Temp have issues with the sensors and gauges that are being sold. So I have some good info for you and since I have a 78 we should have the same gauge in the dash and 2" thick one and the dial face differs too. Actually the FSJ full size jeep and the CJ use different gagues and sensors.
When I installed my rebuilt
AMC 258 i6 / 4.2l , wanted to know oil press on start up, as we set the initial time, addressed any immediate needs during start up and break in. I had the jeep oil sender and gauge........ BUT I also put a mech gauge right next to the oil sender.... I could see the gauge under hood and during the full break in. I will show a few pics on how to do this. I also used the mech gauge to fine tune my jeep gauge/sender.
I tune my gauge / sender because it was dirty inside, the glass was cloudy, the indicator needed some new paint. I uncrimped my gauge... cleaned, painted needle, cleaned glass, pryed off the needle. During a cold start (max pres) I read the mech gauge and then made the jeep gauge read the same.... jut pushed the pointer on with the same reading... Worked perfect.... I am not suggesting you do this.... just FYI. I feel if you get the correct sensors and your engine is sound it will read correctly.
Read this info carefully and then test the sensors...
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.
PS
sometime in the future I will complete this with pics and a full write up
welcome to the site. :ww: