Just getting back into jeepin. 10 years ago I had a 4.0 XJ that never over heated on me - It had a 180* thermostat and was driven mostly on highway.

New project jeep is 4.0 and I will be doing plenty of low speed trail riding (nothing crazy) and in that application I do not want to have a heating issue. 195* thermostat, clean cooling system, new water pump and new electric fan.

Please correct me if I'm wrong or misinformed...
My understanding is that the temp sensor in the thermostat housing is what controls the electric fan cutting on/off (aside from A/C system) and that when it reaches 210*-220* it will cut the fans on and at some lower temp they will cut off. To me, it appears the sensor is 3/8 NPT.

So would it be advantageous to find a sensor that would function in a lower temp zone? So the fans cut on earlier ,before temps begin to climb, and provide the engine with cooler coolant.

Found this on summit... Painless Performace Temp Sending Untis 30110 - says fan on at 195* and fan off at 185*

Any thoughts on this? Am I not thinking of something I should be? Any reason this is just stupid?

 

Maybe I should clarify - This jeeps runs fine and does not have a heating issue during normal driving. I have not yet put it under a long duration, low speed, high load scenario. I am just thinking ahead. I don't really want to go swapping out to different electric fan options if I don't have to.

 

I believe the PCM controls the fan. the sensor only tells it what temp the coolant is.

 

Agreed that the PCM is what is triggering the fan to come on. I believe it comes on at 218°F.

If you were to install a 195 on / 185 off switch, the fan would probably never shut off. What I did and would probably recommend is to wire a fan over-ride switch in so you can manually turn the fan on when you want extra cooling, and then turn the switch off to go back into automatic mode for regular driving.

 

see post above. Put a fuse in your switch wiring also. Happy trails!

 

Thank you for the input!

 

For what its worth...the 2000/ 2001 fan turns on above 220...approx 223-225 ish. These years do not care about AC input...temp only. It gets this temp input from the coolant temp sensor in the thermostat housing, which also drives the gauge. At 210 the sensor resistance is 675 give or take 50 ohm either way. 220 plus degrees is somewhere in the 500's. I can't access the manuals to get a closer guess. If the sensor you want to get is a switch...it will not work, and if is a resistance sensor then to turn on at 185/195... it will have to read approx 500 ish ohms at 190...giving you a temp reading of 220+ on the gauge. With the single sensor driving the gauge and fan control, you can't have it both ways since the computer is looking for a 500 ish resistance reading to turn on the fan..the gauge will match the resistance reading. Do you have functioning ac?

 

Thank you! That was an excellent answer. And now i understand better. Yes A/C works.

 

The Painless 30110 sensor (on at 195°F, off at 185°F) is a solid choice for trail use. It’ll kick the fan on earlier, helping avoid heat soak at low speeds. Just confirm it’s compatible with your XJ’s wiring/fan relay setup. No downsides if your cooling system is healthy. Good upgrade for crawling.

 

Pretty sure you don't want to mess with the sensor to send the wrong temps to the ECU as it can also affect how the motor runs. It's used to determine close/open loop status for adjusting fuel trims and timing. You really don't want to put a different sensor in there.

 

All the above info is only accurate if you use the factory sensor / computer and wiring harness to drive the fan. . If you get an aftermarket sensor system that has its own sensor / controller and power supply systems..then if you disconnect the fan from factory wiring and use the new set up...everything is happy. . I do not have ac in my 01 but did in the past. I jumper out the fan driver side of the freon high pressure switch and anytime I select an ac mode...the fan runs. I am assuming that you will not want to run ac on the trail. Then its easy...jumper both sides of the high pressure connector and the compressor will not turn on but the fan will when selecting an a/c mode

 

Sounds like I'll be leaving the sensor alone. It may not be an issue anyways - just thinking ahead. Running a jumper wire seems to be the safest/easiest solution if needed. Thanks for the insight!

 

Adding this to help anyone else. Its a great write up on wiring in an override switch for the electric fan without potential of back feeding 12V through the wires.

https://www.cherokeeforum.com/f51/ri...-e-fan-212243/

 

That's the same write-up I used for my override switch. I did it about 8 years ago, and it's worked great ever since. I'll flip it on when driving off-road, on the beach, or anytime I want to keep temps down in hot weather. I've got an aux transmission cooler mounted in front of it, so the fan helps keep the trans temps downs as well. The other nice thing about having an override switch is you can run it with the engine off after you've parked on a hot day. This helps keep temps down under the hood. I've got it wired on switched power, so there's no fear of leaving it on a draining the battery, as the key needs to be ON or ACC to energize the fan.

 

Heck yeah! That's awesome. Glad to hear that it works for you so well!