Testing an electric fan switch

73 Mike

I'll drive it someday
Joined
Mar 30, 2008
Messages
714
Location
Boston, MA
I've traced my non working Spal fans to the thermostatic switch mounted in the head. I think that the one I have is set at 185 degrees. It's certainly possible that I got goo on the threads and am not getting a clean connection but it's also possible that the switch is faulty.

Is there an easy way to heat the switch up to test for continuity? Just put it in boiling water? I don't really want a burn on my hand to match the one on my leg. :gurney:

I also noticed that my RPMs drop a little when the fans come on. Looks like it's time to put on the 130 Amp alternator.
 
Pull the connector and ground it to the block, if it works now it's the thermostatic swtich

Did you wire it relay switched or not?
 
Pull the connector and ground it to the block, if it works now it's the thermostatic swtich

Did you wire it relay switched or not?

I did wire the relays switched. The fans come on if I ground the top of the sensor to the manifold (with the ignition on only), just not when the engine heats up. It can only be the switch. Just don't know if it's a poor connection to the ground through the block or a faulty sensor.

In either case, I need to remove the sensor. I'd just like to test it before cleaning and reinstalling it. I also have to remove and clean the adapter. I suppose I could measure the resistance between the block and base of the sensor to see how clean the connection is, but unless it shows continuity, I'm not sure how I'd interpret the results.
 
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Did you use teflon tape? If so, use thread sealer and only on the 1st couple of threads

What temp is the switch? Maybe it's one of those that come on way above 212, there are tsome that are as high as 230, maybe even higher.

I've always had good success with the Jet ones, they are weatherpack type, much better than the normal spade
 
Sealant will not interfere. The threads cut a clear ground path just fine.
Sensors are RTD devices that vary resistence proportionally to temp. Their variable output modulates devices such as gauges or PWC devices.
Switches are either on or off. This is what you seek to drive a relay system.
Hook a meter between terminals. It should read infinity. Clamp in vice, and slowly heat with a soldering iron. It should close and read very low resistence at temp. Boiling water applied is also a good test.
 
If you put too much teflon tape on it it will not work, I came across that very issue on Xanders 77 where the prev. owner installed a switch with a bunch of tape on it. The fan would NOT turn on.
 
If you put too much teflon tape on it it will not work, I came across that very issue on Xanders 77 where the prev. owner installed a switch with a bunch of tape on it. The fan would NOT turn on.

I believe you Marck, I just have never had an issue. NPT threads tend to cut the sealant, leaving only the voids filled with sealant.
Perhaps the excess prevented proper torquing of the switch body.
 
Quick update as I drain the coolant.

It is definatley a switch. Should only be off or on (full or zero resistance).

The side of the box says that the switch is 195 degrees. Pretty hot to acheive in a pot of water but certainly possible. The soldering iron suggestion may be safer. Certainly safer than the torch I was considering using.

I used a little bit of thread sealer (Permatex) but only on the last few threads. I did have to remove the sensor when I replaced the headers at which time the sealer may have spread. It's possible that I'll see this when I remove it later today.
 
The sensor looked pretty good when removed. I was able to heat it enough with the soldering iron to trip it until continuity. Guess that wasn't it.

It's a little late tonight so I'll take it for a spin tomorrow night and heat it up. Maybe tightening all of the contacts will help. :banghead:

Ultimately, I'm going by the temperature gauge on the console and there certainly isn't any reason to believe it's correct. Maybe I just didn't heat it up enough.
 
Fast easy way to warm it is just to lay a big towel on the front of the radiator and/or condenser to block air flow. Watch the tstat housing with an ir gun so you don't cook it. Test the accuracy of your tstat and gauge while you're at it.

I've taken temp senders out that had half a roll of teflon tape on them and then barely screwed in tight enough to hold, no contact.
With the 3 wraps recommended and tight enough it should act as Bird described.
 
You should never have to use any sealer anyways. I never used any sealer on any tyep of GM sensor/sender and never had one leak.
 
You should never have to use any sealer anyways. I never used any sealer on any tyep of GM sensor/sender and never had one leak.

Look again. The factory replacement senders have a coating of red sealer preapplied.:drink:
 
Yes, there's always a little red sealant on those snders, only 1st couple of threads though.

Without using sealant you have to torque dow the pipe thread real tight for a leak free connection, might spell trouble when you need to remove it sometime in the future. those brakk hex thnigs strip rather easy if they are hard to break loose and with the confined space it can be a PITA to get a good leverage on it too
 
where is your temp switch located ? Towards the back of the heads ? That area runs cooler than the front (at the thermostat housing). I have two gauges, one at the rear and on at the thermostat, the two gauges at the top left, rear is at 180, front is at 210...... maybe you're just not getting to 195 where your switch is....

214a63e9bdde2be.jpg
 
where is your temp switch located ? Towards the back of the heads ? That area runs cooler than the front (at the thermostat housing). I have two gauges, one at the rear and on at the thermostat, the two gauges at the top left, rear is at 180, front is at 210...... maybe you're just not getting to 195 where your switch is....

That's was a possibility though it is towards the front of the head.

I got home early enough to take it for a spin. It's still 91 out so didn't take long to get warm. Got up to 200 very quickly and stayed there. Fans seem to be running fine now.

Thanks for the help anyone. Not sure what the problem was, but it appears to be solved.
 
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