Just chiming in here: my '96 V8 ZJ also runs cool, though I haven't really done much to fix it. As far as gas mileage goes I get around 11-13 around town.

 

Old thread, i know, but I have the same problem.
did you find any solution?
I found a vacuum leak on mine that fixed the gas smell and rough running. I got new T-stat and have checked the heat with a ir-gun and its running at only 70-75C (160F)
the fan clutch seems to be working fine also.
i have no clue what can be the problem?

 

I think you should remove the thermostat and replace it. If it is stuck open it may cause the engine temps to remain too cold like that. They are inexpensive to try. Its just a little work to get to them on the Jeeps.

You can pull the one out that is in there to place it in cold water pot on the stove and heat it up to see if it does anything, or is stuck?

 

I have tried this, the T stat is good.

 

That is good you have the tstat ruled out and know it is not the problem.

The next most likely thing to cause the Jeep to stay out of closed loop mode running rich and cool is the engine and/or coolant temp sensors... That is what should be totally ruled out next in my mind. An IR reading is not enough information to rule a temp sensor out. The best way to check this is with an OBDII scanner doing real time data feed function tests to look and see what temperatures your Jeeps PCM is actually interpreting the data to be.. That would be the most definitive way. Correlate the data you find out here with what temps are seen on the guage, and with the IR readings.

In my opinion, the next most likely thing to check is going to be the oxygen sensors to make sure they are not stuck. Faulty O2 sensors may keep your Jeep running outside of closed loop too. The O2 sensors can also be tested with a scanner.

Another thing to check when this type of thing happens staying in closed loop is MAF sensor. Except, ZJ and WJ Jeeps do not have a MAF sensor. They have MAP sensors instead, and these MAP sensors should not be the reason..

 

I don’t think there is an OBDII plug in the zj 95’ can this be done with some other methood?
but I will check the O2 sensor somehow and rule it out.
But my main question was if an vacuum leak and/or bad PCV valve could cause the problem. I have fixed that problem, it was running rich because of it, but I have not had a chance to test the jeep propperly, since im doing some work on the front diff.

 

You are right. I missed the year being a 1995. 1998 and above has the ODBII and PCI bus communications data systems. This was the year when the manufacturers went to a new universal data code reading system I think. Chrysler had a different type a CCD bus for their vehicle data systems communications network before the PCI bus. There are variants to each bus with different layouts. I do not know much about the CCD data bus/non-OBDII systems?

(edited):
There are voltmeter test procedures used with IR readings. There are specifications outlined, but I think they are specific to each model temp sensor in a way.. to follow.