Only use the 83501426 stat from the dealer. Most of the rest are junk. I went through 3 Stant Super-Stats before finding this out.

 

i drive 15 minutes to work. the drive is 3 miles at 60 mph then 35 mph stop and go through town then 4 to 5 miles at 60 mph. last week i never broke 130 on a trip to work.

mileage is 205K. not sure on the injectors or the O2 sensor. from talking to the previous owner i would suspect the injectors are stock. he had all of the engine work and maintenance performed at the dealership. in fact, he had just had the top end of the engine gone through at the dealership. he was only selling the xj because of back trouble and his doctor said he shouldn't be out bouncing around in a jeep. the o2 sensor didn't cross my mind because it hasn't thrown a code. can an aftermarket exhaust cause the o2 sensor to read wrong? it has a flowmaster muffler with a turnout in front of the rear tire

i have an infrared thermometer and have verified that the temp on the gauge in the dash is within five degrees of the thermostat housing. i have checked it through the whole range from 100 to 210. that said, i have bought a new sending unit and plan to install it today as a "hail mary".


my next step will be to buy a tstat at the jeep dealer. if it still doesn't work i will look into the O2 sensor theory and then the injectors.

 

after reading your post again it crossed my mind that you might have been referencing a second temp sensor. does the pcm use a seperate temp sensor to control fuel/air mix? if so, where is this sensor located?

 

The temp gauge sending unit is in the back of the head, drivers side. PCM coolant temp sensor is in the t-stat cover.

 

that's useful info. i wasn't aware that there were two. this means when i verified the temp at the tstat housing with the dash gauge i wasn't ruling out the sensor on the tstat housing like i thought. i will replace pcm sensor TODAY and pray for a miracle. thank you.

 

I'm really confused now. What temp was IR showing when pointed at the stat cover?

 

it has been six months since i did that. i started the engine cold and aimed the IR at the thermostat housing. i watched it climb to 100. once it broke 100 i would check the gauge in the dash periodically. the gauge in the dash always matched the IR. so i assumed that the sending unit in the tstat housing was working properly. i thought that the dash gauge got its signal from that sensor. now you have informed me that the dash gauge gets its signal from the sensor on the firewall end of the head. so i never really tested the tstat housing sending unit. it could be bad and sending a false signal to the computer.

 

Starting to make more sense now. Did u continue to verify with the IR to confirm proper coolant temp?.....that stat(s) were functioning correctly?.....and that the dash gauge reading was probably wacked all along? U need to get the oil pressure verified with a mechanical test gauge, not another electric oil pressure gauge/sending unit.

 

during the previous test i mentioned i monitored the dash gauge and the tstat housing till it planed out at 205. this was a warm day idling for a LONG TIME. so i feel i have verified that the dash reading is correct.

today i replaced the sending unit located on the tstat housing. i then let it idle until it reached 150 degrees (confirmed with IR on tstat housing). next i drove it for approx 20 minutes at highway speed and through town. dash gauge now read about 130 and i confirmed this with the IR. the temp outside was 68.

i am going to try one more tstat (from dealer) and then the O2 sensor. after that i guess i will take it to the dealer and have the injectors checked.

 

I'm baffled it can actually run 130 with/without a t-stat and have a good heater. Almost want to question your IR accuracy.

 

i am not really worried about the heater. when i say it heats well enough at 130 i don't mean it would keep you warm on a 30 degree day while driving in shorts and a t-shirt. but i do know that if you let it sit and idle till the temp reaches 200+ it blows as hot as it did from the factory.

the 130 running/150 idling temps are what it does right now. in the middle of the summer it is 160 running/200 idling.

whoever mentioned the over-fueling as a cause of decreased running temp has caught my attention. i have a lot of black carbon residue in the tail pipe and poor fuel mileage. i need an onboard diagnostic display of what is happening while the engine is running. i have checked the codes in the past. the only code that has popped up is low running temp. i knew that already.

 

Did u verify/test either of the t-stats?

 

That would be me. I would refer to Djb for a cooling problem myself! Even with the MAP, the cts, and iat, and 02, completely ritch/out of whack, it should STILL get to temp if the T-stat does not allow coolant flow.

How could it not? Is it down hill both ways to work?

What kind of driving do you do again? I just don't see it eventually warming up. It's just physically imposable.....the engine makes heat. It WILL get hot, unless the thermostat lets the heat out towards the radiator.

It CAN take allot longer and even not really get there pig rich...MAYBE...if you never really go a ways....The MAP is the first, most important mix sensor

AH! (DUH), 95! Your MAP is still on the firewall? Listen. If you have a little rubber plug on the inside of your throttle body with a small line running back, then up to the MAP sensor on the firewall, make sure that is FLAWLESS. The MAP will tell your PCM to dump extra fuel if it senses a drop in vacuuum. Get me? Crucial, that tube. Plugged, cracked, or otherwise, f-d-up it will run rich.

MAP is King. Tells the puter you put your foot down, opened the throttle, and made the manifold vacuum drop. Through a flimsy little brittle tube for us Renix guys, then the MAP is on the TB, 96 on?, Don't know what you have, but the pre 90 MAP tubes are a real weakness. Plugged, cracked or off, and you are pig rich.

 

no i did not. i had it in my head that the odds of getting a bad stat are low. surely i wouldn't get 3 bad ones in a row! i should have tested them before i chunked them. i did another test when i got home tonight. i let it idle till it quit gaining temp on the dash gauge. the gauge planed at about 150 (this is after 20 minutes of mixed driving and 10 minutes of idling). i then turned the heat all the way up, the blower on high and blowing out of the vents. i stuck a pen thermometer in the vent and it planed out at 143. that is using fresh air not recirculated. i think this is another confirmation that the dash temp gauge is telling the truth.

i am not worried that the tstat isn't opening. the exact opposite is what i am thinking (if the tstat is the culprit). i think it is opening at a very low temp. the stats i have been through have been in the closed position when i removed them. if they were stuck closed i would have the opposite problem, overheating.

the map sensor theory sounds promising. i have decided to take it to the dealer. i read on another forum last night that performance cooling additives can cause thermostats to act funny. the PO may have used some of this. i am planning on having the dealer flush the cooling system and replace the thermostat with one of theirs. i will have them check the MAP system connections if i haven't done it already. that's the kind of insight i am looking for. all of my mechanical experience is with non computer diesel and gas engines, so when it comes to o2 sensors, map sensors, bad injectors, etc i am pretty much lost.

thanks again!

 

"pig rich".....that's funny