What's normal temp

[tugboat95]

As the weather gets warm I'm noticing that my 4.0l is running about 212 to 215 according to my gauge. I'm not sure what it was a few months ago when I first bought it since I didn't bother looking. Seems a little warm to me but It runs great. It's a closed system and is in serious need of a flush which I hope to give it in the next few days to weeks.. As part of it I plan to install a new Tstat. Which is better for these 4 liters, 185 or 165? Seems I have 2 choices. My diesels run at 165 and my 350 gas engine runs at 190. Fans are working as they should but one of the shrouds is missing. What should I be shooting for with the planned work. Or should I go further. Anybody know where is a good spot on the block to shoot with an infrared for a consistent temp to double check the gauge and what should it say at that point? I usually double check a certain joint in a coolant line on my diesels and it's about 5 degrees hotter than the gauge. I've learned over the years every engine has its own normal. I just have to learn it. These 4.0L s are a little different animal than I'm used to. Gotta learn a new normal. Any pointers are appreciated.

 

89 Comanche

Eliminator

2wd

4.0L

5 speed PukeGoat

Factory Original

 

 

 

[87MJTIM]

The stat should be 195*.  That is the temp when stat opens.  Putting in a lower temp stat will only slow the engine from reaching proper temp.  The 4.0 is designed to run about 210* as measured from the temp sensor to the ECU.  This is different from the sensor for the gauge/idiot light.

 

A recent thread on the proper stat was beaten to death a few weeks ago.

 

The e-fan will not kick on until the temp (as measured at the fan control switch in the radiator) reaches a certain temp.  This switch is on the cool side of the radiator.  So the coolant temp has dropped from when it came out of the engine.  My engine temp gets up to 215-220* before I hear the fan kick on.

[Minuit]

I would consider anywhere between 195 and 210 to be acceptable under most circumstances. A little higher is probably fine if it's an extremely hot day or if going up long hills or other high engine load situations. A larger radiator will make the temperature more stable.

 

Thermostat for a 4.0 is 195. Do not use any other temperature thermostat. The factory Renix cooling fan comes on if the A/C compressor is on or coolant temperature is 190 degrees F... in the cold side of the radiator. Too late at that point.

 

If you have factory gauges, use MOPAR sending units only. In that case, the gauge needle should be somewhere on top of the "2" in "210" during all normal driving. Aftermarket sending units tend to result in an unreliable or inconsistent gauge.

 

IR temperature gun on the thermostat housing or upper radiator hose near thermostat housing.

[tugboat95]

Thanks for the info. To go the next step. I'm planning on having the entire coolant system flushed. I really want the engine passages as clean as possible. Has anyone had any issues flushing out one if these old radiators. I'm aware of the bleeding of air issues of a closed system. Is the radiator (it's in good shape visually) going to hold up to a machine flushing it under pressure?

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[Pete M]

ah yes, the "3 sensor temp system" on the ol' Jeeps.     why on earth is it this way?  no one knows...  

[87MJTIM]

9 hours ago, Pete M said:

ah yes, the "3 sensor temp system" on the ol' Jeeps.     why on earth is it this way?  no one knows...  

Government regulations to triple check everything. Of course, like government, none of them communicate with each other. 

[AZJeff]

Flushing radiators can be hit or miss, as it all depends on what sort of residue is clogging the radiator to begin with.   For example, out here in AZ, our water is VERY alkaline, and radiators that are filled with that water WILL develop lime residue in the tubes that will eventually clog them.

 

The only thing that removes lime residue are acid flushing agents, and acids can and will attack the metal of the radiator as well as the lime inside the tubes.   That means the flushing process might result in a radiator with holes in it, or worse yet, one that does not leak, but one that has weakened walls that will burst once it's put under pressure and temperature.

 

Bottom line---flushing may or may not improve radiator performance.

[Pete M]

and that is precisely why distilled water is highly suggested for cooling systems.  

[AZJeff]

6 hours ago, Pete M said:

and that is precisely why distilled water is highly suggested for cooling systems.  

Tru dat.  But most former owners probably did not follow that rule.

 

Proof of that is the “custom” wiring we see on older MJ and XJ vehicles, using twisted wires and electrical tape, or wire nuts.  An owner that would do that wouldn’t worry about distilled water in the cooling system😢

[eaglescout526]

I have had good results using 50/50 of vinegar and water in a radiator to help clean out all the deposits and such. The factory radiator in mine is one I used the mixture on and the engine stays at 210*.