Aux Fan Temp Switch Bad? Or

Finally warm enough to test out my new Aux fan. I installed an Aux Fan Temp Switch two years ago. It comes on at 190F and turns off at 174F (a bit lower than OEM). As expected, my Aux Fan switched on with coolant temp at 201F (190F radiator temp). The coolant temp started going down, but when coolant temp hit 199F, the Aux Fan switched off. About 15 seconds total. Over a year ago, when I first installed the temp switch, it would switch on at 201F, and switch off around 185/190F, if I remember right.

My Aux Fan Temp Switch is only 2 years old, so I can’t believe it could be faulty already, but maybe. Before I invest in a new switch, is there a relay or something that controls the Aux Fan that may faulty and switching it off prematurely? Or does the wire hookup to the temp switch matter?

Thanks!

Looks like your operation is similar to mine. I put in a new aux fan last fall and it really gets the temp moving all over the place like you are experiencing. I put in a 12 inch 4000 cpm fan and with all running over periods of time in up to ambient in the low 80 deg F, my temp gauge stays below the ’N’, a temp of typically 205 deg F. (Water rail) When not doing an extended HWY run my gauge also goes all over the map until it stabilizes. In street driving it even gets wider excursions on the temp gauge. Probably because with different speeds from stopped in traffic to typically 40mph, the cooling efficiency can be anywhere. I also have the problem of long extended hill climbing or downhill coasting at elevations between 1800 to 3500 ft altitudes. So there is nothing I can evaluate unless I’m on a highway run. At ambient temps below 78 deg F my temp gauge never gets to ’N’ regardless of the type of run. I can run below the ’N’ on the gauge at ambients up to 90 deg F and at speeds of 80mph + for as much as 30 mins or more at sea level, so I’m pretty satisfied but then getting into 55 mph at altitude runs and long hill climbs at 20mins after a sea level HWY run, my gauge does go to ’N’ and at times because of the addition of stop and go, I do get gauge readings above ’N’ but nothing I can do about that because of hill climbing at 55mph which includes stop n go. Obviously I have a unique driving environment.

I tend to run pretty stable between 190-195F. On warm days, I can hit 200F at idle, which is why I want my aux fan to turn on anything above that.

I just remembered, last fall when my old aux fan started not working. The fan was seized, and so too many amps would keep blowing out the fuse. Perhaps that messed up the temp switch?

Seems funny that a newer switch would be faulty. Is your car running or turned off when it shuts down?
I would think the only two external sources which would control your fan would be the AC (which you’ve removed for now) and according to the book the bootstrap circuit which would shut it down when the car is turned off.

the test is while it’s running. My 88 automatically turns on the Aux Fan if the climate fan switch is on, even without my AC Compressor. It works fine then, stays on until I switch climate fan off.

I could see my temp switch being bad due to my shorting issues last year. Switches are cheap, so may as well try. I’ve also located some different temps that I’d like to try (90C-80C instead of the OEM 92C-82C) Tridon seem like a good one, but are they only available in Australia!?

You’re right , the switches are fairly cheap, I put a lower temp one in mine a few years back, I was thinking it was around 88C.

where did you find it? I’m having trouble locating one (besides UK and Australia). At least i know it’s M22x1.5.

I thought you might ask so I went looking through all my receipts to get a part number and confirm the temp settings.
I bought it from V12’s.com but unfortunately I don’t think they’re around anymore.
It’s too bad cause I ordered my fuel injector wiring loom from them as well and they did a great job. Saved me a lot of work.
My fan switch has worked flawlessly, and they did a lot of electric fan kits which you’re currently going through at the present.

Ok, had a DUH moment.

I realized if i short the two wires going to temp sensor, i can see if something else is turning off fan.

It stayed on. So obviously bad temp sensor. Have ordered new one.

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I don’t quite understand Greg… If you short the two wires on the temp sensor the fan is supposed to turn ON.

Yes, the fan is powered directly via the A/C relay.

Greg , I think is the bad boy you want. Just go to James Loves XJ-S website and go to the the parts section.

thanks, but that’s the standard one, with a 92C-82C range, and easy to find. Comes on when coolant exiting the radiator is 92C/197F, when my engine coolant at thermostats could be around 210F+. I’d like it to come on a bit sooner.

I was looking for the lower range, 88C-79C. This will come on when my engine coolant is around 200F+ Found two suppliers in the UK, so have ordered one.

WIth my 190F thermostats, I’d like my engine to run steady between 190F-200F. This setup should achieve that.

My original issue was that the temp sensor turned ON the fan at the right temp, but then the fan was shutting down in 15 seconds well before the lower temp was achieved. By shorting the wires, I was able to see if something else was turning off the fan prematurely. Nothing did. So I concluded it must be the switch.

You’re right Greg, I was looking for the temp rating. I did manage to get the lower temp rating for my own car but they didn’t mark the model number or temp rating on my invoice. Based on Kirbys book, my first major project was pulling the radiator, replacing banjo bolts, swapping out yellow fan and replacing aux electrical fan and temp switch.
I would do a few things different if I did it all over again. I would have upgraded the electric fan like your doing. Might be a good project this summer.

Try one for a Land Rover ‘95 Discovery/Defender 3.9L… I think they come on sooner.

You can get various NPT switches from American Volt. I’ve tried a 200 on/185 off on my primary electric fan that works great.

You do realize that the fan switch is in the cold portion of the coolant circuit, and when the aux fan comes on the coolant is supposed to get cooler in a big hurry?

there’s no WAY it could go from 190F to 174F in 15 seconds, unless I have the fan of all fans. If so, the coolant temp at the thermostats should have followed soon afterwards but they only went down 2F, from 201F to 199F.

The thermostats are on the hot side of the coolant circuit. To move them, you’ve got to change the temp of the entire block. Not so the fan switch; you only have to change the temp of one hose full of coolant.

I know what you mean. Based on my switch, the thermo switch is testing what coolant is coming out of the radiator. My switch turns on at 190F. It just so happens, the coolant that has gone through the block and reached the thermostats at this exact time is now 201F.

That 201F coolant going back into the radiator is now getting extra cooling from the aux fan, until it hits 174F coming out and the aux fan shuts off. If the coolant coming out of the radiator has cooled by 16F, you would think that coolant entering the block and hitting the thermostats would be much cooler too.

How could my aux fan cool the coolant in the radiator by 16F more in just 15 seconds, yet the coolant at the thermostats is reading only 2F lower (allowing a delay in time)? Does not make sense. The switch must be turning off too early.

I’ve easily seen my coolant temp of the block at the thermostats go down 10F in like 20 seconds just by moving.