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Discussion Starter #1
Hi All,
I have a 1995 Xplorer and was driving it in my yard pulling a light load of sticks on a plastic sled for about 20 minutes and the overheat light came on but the fan did not. The atv was shutdown immediately until it cooled off which wasn't long because it was around 25° F. Once cool it was started up and driven into the garage.

The front end was elevated on car ramps and the engine run with the radiator cap off. A bunch of bubbles could be observed in the radiator as the engine ran which indicates to me that there was air in the system and it was air locked so coolant was probably not flowing to the head. Once there were no more bubbles coming into the radiator the radiator cap was replaced and the vent on the top of the head was loosened and coolant immediately started to flow out so the vent was closed.

After about 30 minutes of medium to hard driving everything was up to temp but no overheat light came on which was good but the radiator fan also was not on. So back to the garage and the fan was tested and it works fine and the radiator thermal switch (4110178) to the fan was removed for testing. A VOM was connected to the output of the temp sensor set at 200 Ohm range and the meter indicated that the switch was open. Then the end of the switch was suspended in boiling water and it took about 40 seconds for the switch to close. I tried to duplicate how coolant in the radiator would come in contact with the switch by just exposing just the end of the switch a couple threads deep into the boiling water.

As most people know who have these older atvs, thermal fan switch 4110178 is no longer available from Polaris.

My questions:
1) Is this temperature switch still good? Is 40 seconds in rolling boiling water fast enough to close the switch and turn the fan on?
2) What are the specs for this switch? It would be good to know at what temperature the switch closes.
3) Are the aftermarket switches on Ebay any good or even worth considering? I did find a new old stock Polaris OEM switch for around $70.

Thanks
 

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I do not have any answers to your questions. On my 500 I installedva relay for the fan to run off of. It was my theory that running the fan off the switch was a switch killer. Running off a relay, all the switch does is trigger the relay. Similar to what is done to save the oil pressure switch on the older GM 6.5 diesels
 

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Discussion Starter #3
Hey JR,
That is a great idea. Why have all the energy to drive the fan run through the switch? A relay is a brilliant idea. Something for me to consider especially since this part has been out of production for so long. I'll take a look at some new relay wiring options when it warms up this spring.

Thanks!
 

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Did you top up the radiator after getting the air out?
The switch will not work unless submerged. Those older machines with the switch in top of the radiator were sensitive about making sure the coolant is completely full with no air pocket.
A $12 Chinese fan switch will do exactly the same thing as a $70 OEM
 

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Discussion Starter #5
Hi Polman,
Yes. I topped it off right to the brim of the radiator opening so that a little coolant was pushed out when the cap was installed. So I think I am good there.

Good to know that the $12 version will be just as good as OEM. The original switch has been reinstalled and I'm going to monitor the temp and fan to see if the fan kicks on. If it doesn't when it obviously should I'll order the cheap switch and give that a try.

Thanks
 

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The fan control (SSCB) unit needs replaced - when the thermal switch tells the SSCB it's hot (about 190 degrees), the fan turns on - when the temp hits about 205, the SSCB turns on the hot light and kills the engine. I'll get the resistances and actual design temp limits in the morning.
 

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I must correct myself - the 95 was pre-SSCB

The 95 Xplorer has two thermal switches - one in the radiator to turn the fan on and off and one on the engine to turn the hot light on and off - neither one is connected to the ignition to cut off when overheated.

The radiator thermal switch should be tested by suspending in water and heat the water - the switch should close at about 174* F and open at about 154* - the hot light switch closes at about 205*.

I took it from your narration that the engine cut off when the hot light turned on - I gather from re-reading that when the hot light came on you shut the engine off.

Placing the switch in boiling water means the switch material has to heat before the heat penetrates to the core and activates the switch. 40 seconds is not unrealistic. A better test is to heat the water with the switch immersed - how long does the water have to heat to get the switch to turn on? Use a candy thermometer to monitor the water as it heats and record the temp at which the switch closes and then remove the heat source and record the temp the switch opens at. If it is near the specifications, then it is fine. There is a possibility the hot light turned on before the coolant temp was hot enough to activate the fan. You can test the hot light switch the same way as the fan switch.
 

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Discussion Starter #8
Hi Latebird,
I really appreciate your insight and detailed description. You truly are a wealth of information. I agree that your method of testing the thermal fan switch is much better than what I did which was placing a room temperature sensor into boiling water and timing how long it takes for the switch to close.

I'll remove the sensor from the radiator and conduct your experiment monitoring the switch closure as the temperature rises in the water. Then I can compare it to the specifications you provided. I might as well toss in some ice after it closes to see if the switch opens at the correct temperature as well.

Regarding the over heat light. I think it performed just as it should. If the coolant system was airlocked the head temperature would rise very quickly and the radiator fan switch would not turn on. By "burping" out the air in the system I think I resolved that problem. I think this was confirmed when I couldn't get the over heat light to come back on even with extensive driving.

Regardless testing both thermal switches will be the plan for this weekend. In addition, if there is a problem with one or both of the thermal switches, I will conduct the same test with replacement switches before installation. That should save me some grief if I am sent a bad switch

Thanks again
 

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FYI, I’ve had a fan switch that passed the water test, but still wouldn’t run the fan. It just wouldn’t let enough power through when activated to power the fan, even though it did activate and deactivate at the proper temperatures according to the ohm meter. A new fan switch fixed the problem. They’re pretty cheap anyway, so I just keep a spare since I have several ATV’s that use the same one. And they do seem to all fail eventually.
 

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Discussion Starter #10
Hi Micoviso,
This is where having the thermal fan switch just flip a relay that powers the fan probably lowers the failure rate of the switch. So much less power needed for a relay versus the fan. Or, just keep a few spares around like you said.

If my thermal switch will turn on and off at the correct temperatures and power the fan, I will probably install a relay. It's simple enough to do and hopefully will make my oem part last longer. Heck, the part is only 25 years old, it should be good for another 10 years at least. haha! 😆

Thanks
 

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Discussion Starter #12 (Edited)
Finally tested my thermal switch for the fan on the stove in a pot of water. I kept the end of the switch that goes in the radiator immersed in the water and and the rest above the water to mimic the actual installation as close as possible. See the attached pic for my set up.

Using just a cheap thermometer in the water the temps were;

205° F - Switch Closed
192° F - Switch Opened

These temps were higher than I expected so I repeated the experiment this time monitoring the actual temperature of the switch using a cheap infrared thermometer. The results were;

185° F - Switch Closed
172° F - Switch Opened

I don't know the accuracy/precision of either thermometer but the measurements are close to spec and consistent in temperature difference between open and closed.

Hi Latebird,
I tend to believe the infrared thermometer measurement is closer to what the switch is actually experiencing versus the actual water temp itself but these measurements are a little different than your quoted specs of "close at about 174* F and open at about 154*." So a couple more questions;

Are my measured values close enough to conclude the switch is operating properly?
Is there anything you would do differently with my experimental set up?

Thanks!

001 small.jpg
 

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I think your test set up is fine and the temps I quoted came from the service manual - there are variations between thermometers and test setups - we do not know the liquid or ambient temperature used when the manual was written and the materials the switch is made of has aged and the activation temperatures have likely drifted from the manufactured design - I believe the open and close points are acceptably close to spec
 

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Discussion Starter #14
I think your test set up is fine and the temps I quoted came from the service manual - there are variations between thermometers and test setups - we do not know the liquid or ambient temperature used when the manual was written and the materials the switch is made of has aged and the activation temperatures have likely drifted from the manufactured design - I believe the open and close points are acceptably close to spec
Awesome! I'll reinstall the thermal switch and if things go well I'll be adding the relay today too so all the fan current doesn't have to go through the thermal switch.

Thanks Latebird!
 
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