Running hot fan question

[Colt6920]

My wife's Comanche is running hot, about 220.  The fan needs a new clutch I discovered but the electric fan is not coming on at all.  At what temp is it suppose to kick in?  I'll be trying to diagnose it shortly.  I changed the thermostat and radiator cap already and that did not resolve the issue.  Fan clutch is next.   

[89 MJ]

Have you verified that the temp gauge in the dash is working correctly? 

 

I want to say that the electric fan is supposed to come on at 218, but I do not remember for certain. If it isn't kicking in, I would suspect either the relay is bad or the switch is bad. 

 

When you replaced the thermostat, how did the coolant look? If you didn't do one, it is probably worthwhile to flush the system out really good. 

 

Do you still have the closed loop cooling system or do you have the open loop system? Is the Jeep mostly stock or does it have mechanical modifications? 

 

With my answer to your question and the questions that I asked, I am assuming your truck is a Renix truck.

 

You might want to add details about engine, trans, transfer case, and any mods to your signature.

[fiatslug87]

When you get a chance add the truck to the Registry.

[JZLAJeep]

4 hours ago, Colt6920 said:

My wife's Comanche is running hot, about 220.  The fan needs a new clutch I discovered but the electric fan is not coming on at all.  At what temp is it suppose to kick in?  I'll be trying to diagnose it shortly.  I changed the thermostat and radiator cap already and that did not resolve the issue.  Fan clutch is next.   

As I understand it, the engine is supposed to run at 215 degrees and the electric fan is supposed to come on at 210 degrees. Sounds like 220 isn't outrageously high, but your e-fan should be kicking on.

[75sv1]

Pressure bottle? Also is 220 with AC on?  I'd jump 12 volts to the fan. See if its the motor. 

[Colt6920]

Thanks all for the replies.  The truck is an 89 that has a 96 Cherokee 4.0 HO engine swap.  I replaced the fan clutch and it seems to function properly now but weirdly, no change in temperature.  I suspected the gauge may be reading wrong but verified its really close with a laser temp gun prior to changing clutch.  Put 12v to the auxiliary fan and it came on so replaced the relay and it still does not kick on at 220, which is about the hottest the truck runs.  Pulled the electrical plug from the thermostat housing temp sensor and fan comes on immediately so I guess the temp sensor is bad.  Radiator appears to be newer and no issues.  Haven't verified temp but upper hose is way hotter than lower hose so it appears to be cooling.

I plan to re-verify temps once I have aux fan working properly and see if gauge is still reflecting engine temps.  Also going to verify that the new thermostat is actually working at the 195 degree temp or is I have a bad one.  Appreciate the advice.  Not sure what to do next.  It stays pretty much at 220ish at idle and driving.    

[Colt6920]

Just got done re-checking temps.  Laser temp gun showed the upper rad hose pressurizing and getting hot at 205-208 degrees at the thermostat housing.  Temps cooled to about 196 as the thermostat opened but then climbed to 228.  I pulled the temp sensor plug which allowed the auxillary fan to kick on.  Letting that run gets the temp down to about 203 at the housing.  Sensor at rear of head reads about same as well but gauge reads 220-225 so the gauge appears off.  However, if the aux fan isn't running, it shoots back up to close to 230 or so.  This is all at idle in the garage.  I'm going to replace both temp sensors but I still think its going to run hot and require the aux fan to be on a lot.  Any thoughts based on this new info?  It's a newer radiator, clean with no blockages in the fins.  Temp difference between upper rad hose and lower is about 35-40 degrees so cooling. 

To answer a previous question, no A/C at this time.    

[89 MJ]

When you replaced your thermostat last, did the coolant passages look pretty corroded?
 

Corrosion will make it harder for it to cool, your water pump might not flow enough, your lower rad hose might be getting sucked flat, or your rad might not be good enough, even though it’s new, you also might not be getting enough airflow and need a fan clutch. 
 

By design, you should need the electric fan unless the AC is on. Clearly that’s not what’s going on, but that’s the way it’s supposed to be. 
 

What is the temperature drop across the radiator?