1989 4.0 5 Speed MJ Running Slightly Cool?

[oleskool]

So I’ve replaced the cooling system on my 89 4.0 5 speed because it was running cold as if the thermostat was stuck. It was in fact stuck open and judging by the coolant color and how long this truck was sitting. Now with updated cooling components besides the radiator I’m still seeing it run lower than I remember any of my XJs run. The truck seems to run fine but any ideas as to what this might be related to?

 

[87MJTIM]

I wouldn't trust the gauge.  My gauge seldom gets up to 180*.

 

Is it running in closed loop?

 

Look at www.nickintimedesign.com for the REM diagnostic tool.  This will give a more accurate engine temp reading.

 

(The RENIX Jeep has three separate temp sensors.  One sends a signal to the gauge.  It is located on the rear of the driver's side head.  The second sends a signal to the ECU for engine/fuel control.  It is located on the driver's side of the engine block, below the manifolds.  The third controls the e-fan.  It screws in to the driver's side radiator.  It turns on the e-fan when it detects the coolant temp reaches a preset temp.)

[Pete M]

what degree thermostat did you install?

[oleskool]

22 minutes ago, Pete M said:

what degree thermostat did you install?

Factory temp. I believe that’s 195. 

[gogmorgo]

Looks like it sits at the same temp as my '91 2.5 gauge does. The temperature at the thermostat housing sits just shy of 195°F, confirmed by IR thermometer, and the gauge does still climb higher if I run it with low coolant so I'm not too concerned about it. The factory gauge set isn't intended to be precision scientific instrumentation, and it is 30 years old, after all.

[oleskool]

39 minutes ago, gogmorgo said:

Looks like it sits at the same temp as my '91 2.5 gauge does. The temperature at the thermostat housing sits just shy of 195°F, confirmed by IR thermometer, and the gauge does still climb higher if I run it with low coolant so I'm not too concerned about it. The factory gauge set isn't intended to be precision scientific instrumentation, and it is 30 years old, after all.

Yeah kinda what I figured but thought I would ask. I confirm it gets 195 at the goose neck so I know everything is working. The thermostat opens correctly and the electric fan will kick on when the gauge hits 210. I’ll let this one go and focus on all the other small issues lol. 

[Minuit]

That's where mine is too. I'm using an OEM temperature sender and my gauge is verified. I don't think you have anything to worry about.

 

The factory gauge is no more or less trustworthy than any other temp gauge as long as you do three things:

 

- Use an OEM sender for the gauge. I had an aftermarket sender read a needle high one time and haven't trusted anything but OEM sense.

- Clean the electrical connection at the sender wire, and make sure the connector fits on the sender firmly.

- Cross check the gauge with something else. Infrared thermometers are popular for this.

[oleskool]

2 hours ago, Minuit said:

That's where mine is too. I'm using an OEM temperature sender and my gauge is verified. I don't think you have anything to worry about.

 

The factory gauge is no more or less trustworthy than any other temp gauge as long as you do three things:

 

- Use an OEM sender for the gauge. I had an aftermarket sender read a needle high one time and haven't trusted anything but OEM sense.

- Clean the electrical connection at the sender wire, and make sure the connector fits on the sender firmly.

- Cross check the gauge with something else. Infrared thermometers are popular for this.

Good to hear. I’ll let this one go then. I’ve verified with a infrared thermometer but I wanted to make sure it seems normal. Thanks for the reassurance.