Is my fan overcooling?

[Airsuperiority]

Anyone know of the mechanical fan overcooling the engine? I have a REM reader that indicates water temp gets to about 180F, 165F on shorter drives. My dash gauge hangs out at about (see pic). In traffic it will creep up a little but I have never seen a reading at 210 even through the desert on the highway. 

[75sv1]

Possibly, probably it's the Thermostat. I've had two or three that stuck open or came apart. During the winter, it would get above 125 F.  That's on two different XJs.

[jpnjake]

6 hours ago, Airsuperiority said:

Anyone know of the mechanical fan overcooling the engine? I have a REM reader that indicates water temp gets to about 180F, 165F on shorter drives. My dash gauge hangs out at about (see pic). In traffic it will creep up a little but I have never seen a reading at 210 even through the desert on the highway. 

On my mj I had the same problem, and my heat would barely work, I then replaced my thermostat and the gauge never hits 210 but it goes just a bit low of it, so I would try that if I were you. 

[cruiser54]

Use only Mopar thermostats. They're not cheap, but worth the money for sure. 

[Airsuperiority]

3 hours ago, cruiser54 said:

Use only Mopar thermostats. They're not cheap, but worth the money for sure. 

I’ll look into those then. Thanks! I ordered a IR reader for now. 

[Airsuperiority]

4 hours ago, jpnjake said:

On my mj I had the same problem, and my heat would barely work, I then replaced my thermostat and the gauge never hits 210 but it goes just a bit low of it, so I would try that if I were you. 

Yeah, i had suspected that. But the REM reader I thought reads from a different sensor. Could be wrong. They both are low. Ill try the TSTAT though and see what happens

[Airsuperiority]

So I used an IR gun on the TSTAT housing and it read 193 after a drive. Seems fairly close to the gauge reading on the dash. My water temp reading on the renix engine module reader says 156 though. I don’t really know enough about why that could be reading so low. Anybody have any ideas? 

[Ωhm]

39 minutes ago, Airsuperiority said:

My water temp reading on the renix engine module reader says 156 though

 

Coolant Temperature Sensor aka ECT. Did you try that IR gun on the ECT sensor itself. See what it reads. Using your REM, what are your STFT, LTFT and INJ PW readings? I'll assume vehicle is running in Closed Loop (CL).

 

[Airsuperiority]

1 hour ago, Ωhm said:

 

Coolant Temperature Sensor aka ECT. Did you try that IR gun on the ECT sensor itself. See what it reads. Using your REM, what are your STFT, LTFT and INJ PW readings? I'll assume vehicle is running in Closed Loop (CL).

 

REM reading =153-165F

IR gun ECT= 188.9

ST= fluctuating 165-183

LT= 128

IP width= 5.6-5.8 at idle

 

This is all at Closed Loop. I just put in an 89 ecu so I’m hoping once it gets used to my engine idle circuit it will get to closed loop faster. The O2 sensor could need some cleaning though as the truck just drove from NY to LA.

[Ωhm]

ST has added fuel to the INJ PW probably/good chance because of the low ECT reading. LT holding steady. IP width reads good. Fuel Injection Manual has a crude ECT test. Check it out.

 

ECT sensor testing pg30.pdf

 

[Airsuperiority]

8 minutes ago, Ωhm said:

ST has added fuel to the INJ PW probably/good chance because of the low ECT reading. LT holding steady. IP width reads good. Fuel Injection Manual has a crude ECT test. Check it out.

 

ECT sensor testing pg30.pdf

 

Thank you! 

[Ωhm]

[Eagle_SX4]

I am also having this exact problem. I haven't replaced the sensor yet but my dash gauge reads the exact same. And my R.E.M. usually reads about 180. However as it warms up it will hit 195 then the thermostat opens and settles about 180. The other interesting thing is my volt gauge also reads low by the same percentage. Which is leading me to think there is a resistance problem in the wire harness some where. Over the winter I also noticed my volt gauge was more accurate the colder it was. As the engine warmed up the gauge would slowly drop back down.

[87MJTIM]

The beautiful thing about the Renix era Jeeps is they have three (3) temp sensors.

 

First, the sensor for the gauge is located on the head, back by the firewall.  It sends the signal to the temp gauge.

Second is the Coolant Temp Sensor (CTS),  This is located on the driver's side engine block below the intake/exhaust manifold.  It feeds the coolant temp to the ECU.  The REM reads this signal.

Third is the e-fan temp sensor.  It is located on the driver's side radiator.  It controls the relay that turns the e-fan on and off.

 

The fact that the gauge and REM don't have the same reading is not surprising.

 

My gauge use to read higher - 200*-210*.  Now it reads 180*-190*.  It seldom reaches much above 200* on hot days.

 

The REM will read ~10* higher than the gauge. 

 

My e-fan will turn on when the REM shows 219*.

 

(Before you say the e-fan should turn on at ~195*, remember the e-fan sensor is on the cool side of the radiator.  The CTS is in the hot engine block.)

[cruiser54]

Engine temp SENDER is at the back of the head.

 

Coolant temp SENSOR is located on the driver's side of the block.

 

Fan SWITCH is located in the bottom of the radiator on the driver's side.