Controlling dual electric fans

[Eagle]

I posted in your parallel thread on OEM that I don't like Dr. Dyno's method of tricking the ECM. On the '99 the same temp sensor serves the aux fan and the injection/ignition. Data goes into the ECM and the ECM controls the fan. Dr. Dyno's XJ, based on comments in other threads, is not U.S. spec and thus what worked for him may not work on a U.S. spec vehicle, especially not a '99 with OBD-II.

Okay -- here's a simple solution. The old Renix non-HOs ('87 - '90) used a simple switch in the radiator tank to control the fan. How about taking your radiator to a shop and have them solder in a threaded bung to accept one of those switches? Wire from that switch to a relay for each fan and you're done. I believe the temp setting for that switch is 217 degrees, although my '88 FSM says 190.

 

[Bender]

Eagle,

The descripency in temp's is probably due to the location of the switch. The switch could be seeing 190* on the cool side of the rad while the temp at the engine temp sensor it closer to 217*.

 

[8Mud]

To take Eagles idea one farther, the temp. switch, stock size, comes in various temps. Same switch, same threads, different values. I found my 210 replacement at the junk yard one day (in a Renault I think). I´m sure the right manual, at the autoparts store, has the information on the temp. values, all you have to do is match the thread size (and somewhat the depth).
On my mud truck, I have dual electric fans, soldered the bung (thread part) onto the radiator, cleaned the copper good and filled the cavity with heat conductive paste. The switch doesn´t have to be in the coolant flow, just needs a very good contact with the copper, the temp. difference between the copper and the coolant is minimal.
Just as an experiment, I tried soldering a temp. switch directly to a radiator, no go, 600F or so was too hot for it. My next attempt, will be a heat conductive epoxy and glue that sucker on there.
I have a few broad range, sensitive electronic thermometers, kind of interesting doing temp. readings on different parts of the motor and various locations in the coolant flow.

 

[Roxtar]

Okay -- here's a simple solution. The old Renix non-HOs ('87 - '90) used a simple switch in the radiator tank to control the fan. How about taking your radiator to a shop and have them solder in a threaded bung to accept one of those switches? Wire from that switch to a relay for each fan and you're done. I believe the temp setting for that switch is 217 degrees, although my '88 FSM says 190.

I like the idea of soldering the threaded piece into the radiator. That may be the way to go. I just called a radiator shop who quoted me $30 for that.

 

[Dr. Dyno]

I posted in your parallel thread on OEM that I don't like Dr. Dyno's method of tricking the ECM. On the '99 the same temp sensor serves the aux fan and the injection/ignition. Data goes into the ECM and the ECM controls the fan. Dr. Dyno's XJ, based on comments in other threads, is not U.S. spec and thus what worked for him may not work on a U.S. spec vehicle, especially not a '99 with OBD-II.

My '92 XJ indeed isn't US spec but the only difference in my electronic control from the US spec is a lack of an O2 sensor, so my CTS resistor mod DOES work on a US spec OBD I '91-'95 4.0 with the same side effects that I already mentioned.
The '96+ OBD II system isn't as forgiving when it comes to electronic trickery so it's possible that my CTS mod might cause problems there. My MAP adjuster mod also works fine on OBD I but not on OBD II.

 

[8Mud]

Some of the temp. switches sit pretty flush with the length of the stock thread, some are longer and hang into the coolant flow a touch. If you have the threads soldered on the radiator and don´t plan on opening a hole into the coolant flow, make sure the temp. switch is short enough or the threads are long enough.