Thermo switch for e-fans

Hello, just wondering if anybody is running a thermo fan switch on the cold side of the radiator to run electric fans.
I have mine currently running off the pcm (104*c) but the new stroker runs a bit hotter so was looking at using a thermo switch to run the Taurus fan.
I was looking to keep the stock Thermostat (90*c).
Any suggestions?

You want to be as close to the thermostat housing as possible so that you can monitor the temperature as it leaves the head. The further away from that, the longer it will take to for the switch to react.

Stock Renix (87-90) e fan was controlled from screw in switch in the cold side. 91 model year open radiators still have the port for it to screw in.

http://www.rockauto.com/catalog/x,carcode,1179996,parttype,4312

you'll want something that switches lower than the stock one, but that's what it looks like. Stock one kicks at 160 IIRC. They kick on about 215 on the gauge.

might be easier to just drill the thermostat outlet for another 3/8 npt temp switch and run your fan from that.

87manche said:

Stock Renix (87-90) e fan was controlled from screw in switch in the cold side. 91 model year open radiators still have the port for it to screw in.

http://www.rockauto.com/catalog/x,carcode,1179996,parttype,4312

you'll want something that switches lower than the stock one, but that's what it looks like. Stock one kicks at 160 IIRC. They kick on about 215 on the gauge.

might be easier to just drill the thermostat outlet for another 3/8 npt temp switch and run your fan from that.

Click to expand...

This is what I to my XJ. It did necessitate some fabrication but it could be done.

Through testing, the renix thermal switch which is just an on-off switch switches the fan on at 185* F and off 10* to 15* lower. I did not try the top of the engine water outlet i.e. goose neck. The water temperature there usually remain above the thermostat temperature which would in most cases have the fan running all the time. What I wanted which I assume is what you also want is for the fan to run only when it is needed. I could get in my XJ and drive at highway speed for several hours without the fans running. Note,....My XJ have no mechanical fan. Driving up long hills the water temperature get up to 210* or a little higher according to the gage while the water at the radiator outlet going back into the engine remain below the thermostatic switch setting of 185*.

If you install a switch in the water outlet you would need one that closes a few degrees above the thermostat setting if you do not want the fan to run at full speed all the time which to me would be counter productive.

The renix fan switch is secondary--it still has the mechanical fan for primary. In HO engines the secondary fan switch was replaced by the ECU fan switch. From what I can tell, the OP is asking about using a single large Taurus fan as the primary. The secondary Renix switch would not be suitable.

Fans are set up as the go-jeep write up-big source of info for ausi,right hand drive, xjers.
Vertical mounted Taurus, with the aux fan next to it.
My ausi aftermarket radiator has a bung threaded in M22x1.5 on the cold side a relatively common European temp switch size.
Many cars sold in Australia used a thermo switch in the cold side of the radiator in the 80's and 90's. I imagine USA was the same??
My 80's turbo 2 door mitisubishi had a 90*c thermostat and thermo fan switch that was on at 85 and off at 80. That could be a start point.
I think I'm going to figure out what temp the cold side of the rad is, with no fans, when the PCM switches the fans on (104*c)
Then maybe try somthing 5* cooler than that.
Just thinking out loud here ATM so feel free to chip in.
Thanks and regards,

dirtbound uses a golf mkIII temp switch. It has two outputs. You could use that.

It's mounted in the heater core hose.

ehall said:

The renix fan switch is secondary--it still has the mechanical fan for primary. In HO engines the secondary fan switch was replaced by the ECU fan switch. From what I can tell, the OP is asking about using a single large Taurus fan as the primary. The secondary Renix switch would not be suitable.

Click to expand...

It is true on everything you say about the Renix XJ and the newer versions of the XJ. They all have a mechanical fan as the primary fan. My XJ do not have a mechanical fan since 2004. It have the Derale dual 13" fans triggered by the Renix fan switch retrofitted to the 1996 4.0L by the water in the cool side of the radiator. I have not had a problem with that setup so far.

That location in the cold side of the radiator IMHO is about the best location if you do not want the fan/s running every time the XJ see a bit more load. Try different temperature switches or better yet try an adjustable temperature switch that screws into the water passage. You could then adjust it for the preferred turn on temperature. I think the Renix engineers was on to 'something' when they installed the switch in that position. That 'something' I am trying to duplicate.

87manche said:

dirtbound uses a golf mkIII temp switch. It has two outputs. You could use that.

It's mounted in the heater core hose.

Click to expand...

Funny you should say I found a vw. Transit van thermo switch and put that in the bung hole when I had the whole thing apart, Twin switches ! On 87 off 77 and on 93 off 83.
The cool side of the rad was 100*c when the PCM switched the aux fan when I checked today.
So am leaning toward the 93/83

you're basically saying that you want to wait until the COLD SIDE of the radiator gets to 200 degrees f

what temperature do you think the engine will be?

it will be the same temperature it always is when the factory switch turns on the efan, about 220.

if he switches the fan at 93 then it will pop on about 215 on the gauge. The worry is that the radiator will already be heat soaked and not have any reserve of cooler coolant to cool the motor when the thermostat opens fully. If the taurus fan has enough flow to rapidly cool the radiator, no worries.

Thats alright when the primary fan is also moving air, then its supplemental. If you wait until 200f before you start doing anything, the engine will just keep recirculating hot coolant and engine temp will keep rising. Temps won't start dropping until fan starts shedding heat. I've been there, sitting at a red light and engine temps are climbing noticeably, fan kicks on and temps are still rising.