Cooling Fan Switch And Temp Sensor Recommendations

[DirtySouthXJ]

Hi,

There is a (ebay/amazon) triple electric cooling fan system (semi) installed on my 96 XJ by the previous owner, but he wired it by tapping into a fuse in the PDC (no relay, fans turn on with key on). It looks like an adapter was added where the factory coolant temp sensor was, in order to add a second coolant temp sensor for an aftermarket coolant temp gauge; so currently there are two coolant temp sensors at that location.

Here is what I would like to do:

- End up with a properly wired and functioning fan system.

- Install the aftermarket coolant temp gauge. Currently all I have is the idiot light cluster.

Questions I have:

- Would there be any ill effects if I were to disconnect the factory temp sensor and install a coolant temp switch in it's place?

- Is there a port in the intake, head or block that I can install a coolant temp switch in to turn the cooling fans on, to avoid having to splice an inline adapter into the coolant hose?

If not..

- Can anyone recommend an inline adapter kit (preferably with temp switch, fan relay, wiring etc.)?

- Does anyone know the size of the coolant hose (I'm guessing i.d. to fit over adapter o.d. ? )


Regardless of temp switch installation location..

- I see different coolant temp switch on/off temp specs (on 200°/off 185° etc.), what spec switch should I use in this application (96 XJ 4.0)?

Thank you!

 

[RCP Phx]

Don't mess with the factory sensors as they report directly to the PCM. Most systems of that type mount their temp sensors on the radiator itself and control the fans in stages.

 

[RCP Phx]

As for the separate temp gauge, pick up a t-stat housing with the extra tapped port.

 

[DirtySouthXJ]

Don't mess with the factory sensors as they report directly to the PCM. Most systems of that type mount their temp sensors on the radiator itself and control the fans in stages.

That's what I was thinking, that the factory sensor is for more than just factory temp gauge/cooling fan activation. The radiator is also aftermarket (aluminum), I'll see if there is a threaded port I can mount the aftermarket switch to.

As for the separate temp gauge, pick up a t-stat housing with the extra tapped port.

There is already two units there, the factory temp sensor and the aftermarket gauge temp sensor. I need a third port for the electric fan temp switch. I know small block Chevys have multiple ports in the intake manifold/head/block, I'm wondering if the Jeep 4.0 has similar. I could add a spliced in adapter to the coolant hose but would like to avoid that if possible.

Do you have any idea on what cut on/cut off specs I should be looking for on the fan temp switch? For example 200° fan turns on, 185° fan turns off? I saw a similar triple fan system supposedly for an XJ and it comes with a 180° on 165° off temp switch. Not sure what temp range I need.

 

[RCP Phx]

That's why electric systems monitor the radiator outlet temps, the t-stat controls the engine temp. They typically turn a fan on at about 160-180 and add fans if the outlet temp continues to rise.

 

[DirtySouthXJ]

That's why electric systems monitor the radiator outlet temps, the t-stat controls the engine temp. They typically turn a fan on at about 160-180 and add fans if the outlet temp continues to rise.

Copy, thank you brother! So it sounds like the 180° on 165° off temp switch would work well. I noticed that when powered, two of the three fans come on (with no temp input, fans are hardwired direct to key on power currently). I'm guessing the third is for situations you describe. This is all new to me; I'm used to large single, center mounted, mechanical fans on GM vehicles. If there was a way to swap over to a setup like that on the 4.0 in a XJ, I would.

 

[DirtySouthXJ]

Alright, so doing some more digging..there are supposedly two coolant temp ports on some 4.0 XJ's (evidently depends on year, mine is a 96). One is at the thermostat housing and is the coolant temp sensor used by the PCM for data to control the engine; the other is at the back of the head on the drivers side and is the coolant temp sender for the gauge. I'll have to see if this port (at the head) is present; because if it is, then I won't need any additional adapters etc. to add a third sensor/sender to switch the aftermarket fans on.

Does anyone know the thread size/pitch for the ports at the thermostat housing and at the head?

 

[Unclewolverine]

The one at the back of the head is extremely small. You probably won't be able to use it for any aftermarket parts.

 

[ehall]

Verify that you have the idiot light sender at the back of the head on the driver side (very small threaded stub with a wire on it). That was deleted at some point, maybe 96 for the OBDII swapover (don't remember the year exactly). If you have that, you can replace the sender (an on-off switch) with the sensor for the gauge, and you can probably use that for the aftermarket gauge (they are usually similar but not always). If you don't have the sender, you can also drill and tap the small flat spot in the front of the thermostat housing for a gauge sensor (where I put mine when I swapped in a 99 engine that did not have a threaded port in the head).

The sensor sticking up out the side of the thermstat housing is for the computer, normally it controls the aux fan (and uses the data for other things like determining operating temperature), you should not mess with it. If he added a split bung for the gauge there, it should work for that purpose.

For the fan relay, I use a two-pin switch from late-80s/early-90s BMW models (Four Seasons part number is 36511, the one I bought from NAPA was ATM part number 1435033). According to the specs, it is supposed to come on at 95c (203f) and go off again at 90c (194f) which means it should only come on after thermostat is fully open and go off again when the thermostat is starting to close. That switch is inline with the control side of the relay, so when the switch activates the circuit closes and the load side goes hot. I use an in-line adapter in the upper radiator hose, something like this https://www.amazon.com/dp/B018FY149S (either 40mm or 38mm, don't remember), and then drilled and tapped for the 14mm sensor with a 1/4npt tap (threads are nearly the same). When the thermostat opens (at 195) the adapter gets flooded and the sensor trips, turns on the fans. When the thermostat closes, the fluid in the adapter cools off, and the sensor turns off. The only issue I have is that the fans tend to stay on due to thermostat oscillating at 195. Would like to get a slightly higher switch but never chased one down.

 

[DirtySouthXJ]

The one at the back of the head is extremely small. You probably won't be able to use it for any aftermarket parts.

Well I took a look under the hood and it seems that there is no port on my engine's head.

 

[DirtySouthXJ]

Verify that you have the idiot light sender at the back of the head on the driver side (very small threaded stub with a wire on it). That was deleted at some point, maybe 96 for the OBDII swapover (don't remember the year exactly). If you have that, you can replace the sender (an on-off switch) with the sensor for the gauge, and you can probably use that for the aftermarket gauge (they are usually similar but not always). If you don't have the sender, you can also drill and tap the small flat spot in the front of the thermostat housing for a gauge sensor (where I put mine when I swapped in a 99 engine that did not have a threaded port in the head).

The sensor sticking up out the side of the thermstat housing is for the computer, normally it controls the aux fan (and uses the data for other things like determining operating temperature), you should not mess with it. If he added a split bung for the gauge there, it should work for that purpose.

For the fan relay, I use a two-pin switch from late-80s/early-90s BMW models (Four Seasons part number is 36511, the one I bought from NAPA was ATM part number 1435033). According to the specs, it is supposed to come on at 95c (203f) and go off again at 90c (194f) which means it should only come on after thermostat is fully open and go off again when the thermostat is starting to close. That switch is inline with the control side of the relay, so when the switch activates the circuit closes and the load side goes hot. I use an in-line adapter in the upper radiator hose, something like this https://www.amazon.com/dp/B018FY149S (either 40mm or 38mm, don't remember), and then drilled and tapped for the 14mm sensor with a 1/4npt tap (threads are nearly the same). When the thermostat opens (at 195) the adapter gets flooded and the sensor trips, turns on the fans. When the thermostat closes, the fluid in the adapter cools off, and the sensor turns off. The only issue I have is that the fans tend to stay on due to thermostat oscillating at 195. Would like to get a slightly higher switch but never chased one down.

Thank you! Great info! There appears to be no port at the head in my XJ. I did order an additional tee to add the third unit (sender for gauge) at the thermostat housing. As of right now, I think this will be my quickest and cheapest option to get the fans running, get the PCM the data it needs and monitor temps with the gauge. I will likely rethink the setup at a later time and maybe even go back to the factory mech with electric aux fan setup. Half my battle is figuring out what all the POs have done and what is there v.s. what should be there lol.