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Discussion Starter #1 (Edited)
I need some help.

1968 Nova
454ci, Eldelbrock Performer 2.0 intake manifold, 180 thermostat, alum. radiator.

I installed a 14" Spal pusher fan couple of weeks ago.
I'm on my 4th temperature switch, and none of them worked.
I'm using the switch location on the driver side, couple of inches from the thermostat housing.
The switches are 3/8" pipe thread NPT, going into a 1/2" pipe thread NPT adapter fitting that's installed in the intake manifold.
My coolant temp sensor is down next to the exhaust manifold.

Fan wiring is correct; fan turns on as soon as I manually ground the sender wire from the relay to the switch.
I've actually been testing grounding the sender wire to the outside of the temp switch.
That tells me the switch (& 1/2" adapter) is grounded correctly to the intake manifold, but its internals are not functioning how they should.

My first 3 switches were 210-195. Waited until 220/230 on the gauge - none of them worked.
The one I have on now is a 200-185. Waited until 220 - never turned on.
Again, if I unplug the sender wire from the switch and touch it to the outside of the switch - the fan turns on.

My question is - Am I doing something wrong with how I install the temp switches; or am I the un-luckiest human around, for getting 4 faulty switches in a row?

I know the temp sensor location close to the exhaust manifold reads around 10F higher.
I also purchased an infrared temp gun to monitor temperature close to the thermostat.

Edit:
I forgot to add - I put ThermoCure and distilled water in the system couple of weeks ago.
It was meant to be a 1-2 day flush, that turned into 2 weeks.
I don't want to fill the system up with coolant yet, before I have this switch situation sorted.
So, I've been driving it with distilled water for the last 2 weeks.
 

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Discussion Starter #2 (Edited)
I'm starting to wonder if the water in the system is somehow different than 50/50 coolant when it comes to the temperature reading of the switch. And that the switch is 'calibrated'? to the 50/50 coolant.

I know straight water is a little more efficient in conveying heat, but the temperature at the switch will be the same regardless of the fluid (water vs 50/50).
 

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You can test the temp sender with an ohm meter and a pan of water on the stove. Lots of info on the internet.
 

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Discussion Starter #7
It could be soup in your engine and the coolant switch should measure it's temperature and switch accordingly. Do you have a schematic of the wiring for the electric fan? Also a part number for the latest temperature switch.
I'm overthinking.
Here's the latest:
200 to 185

210 to 195

I'm about to install this:
185 to 170

They all have mediocre reviews, and people seem to have similar issues.
They all just might be trash..

This is the wiring (minus the 'fan on' light, suppressor diode, and manual override switch).

 

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Discussion Starter #8
When installing sender did you use Teflon tape? Sender don't like that won't ground right
No tape used.

Are you sure your gauge is correct?
It's not exact since the sender is in the head, next to the headers.
Car typically runs at 203-205 on the gauge, with a 180 thermostat.
According to the infrared thermometer that's about 190 close to the thermostat housing.

You can test the temp sender with an ohm meter and a pan of water on the stove. Lots of info on the internet.
yea, but then I wouldn't be in the garage every-other-day cursing
 

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When installing sender did you use Teflon tape? Sender don't like that won't ground right just had same problem use good pipe sealant
 

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You are measuring HEAD temp on the gauge, not coolant temp.

You need to move the gauge sensor to the intake manifold so it is measuring the same temp as the fan switch.
 

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The schematic looks OK other than the fuse rating seems low for many of the high output fans out there and the same with the relay. Many are undersized and need to be a higher amperage. As mentioned, I would heat up some water with the sender in it. Use your infrared temperature gun and a multimeter to verify the switch. Hard to believe 3 switches being bad[but many are from China(nuff said)].
 

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Discussion Starter #12 (Edited)
You are measuring HEAD temp on the gauge, not coolant temp.

You need to move the gauge sensor to the intake manifold so it is measuring the same temp as the fan switch.
The gauge is still measuring the coolant temperature. I'm aware its measuring higher than if it's on the intake manifold; I just account for the difference.
I'd also rather have the fan switch closer to the thermostat than my temp gauge.



However, I was not aware of just how much higher the gauge was reading.
I thought it was about 10 degrees; it is actually about 25 degrees.

This is the reason the 210 switches never worked. My car could never get to 210.
The carb's vapor lock issues turn the car off at about 205 :D
It's a safety mechanism many people don't know about.

I did more research on the emissivity coefficients of the different types of rubber, and set my infrared thermometer couple of different ways.
I measured the top rubber hose, right at the thermostat housing.
The engine actually runs at about 180 degrees, while showing about 205 on the gauge inside.

The 200-185 switch turns the fan on at about 225, and off at about 210 according to the gauge inside.
Which is 200 and 185 according to the infrared thermometer reading at the thermostat housing hose.

The temp gauge is Equus 2".

If you have one of those and it's in the head, next to the exhaust manifold - keep in mind it might be reading higher than you think.
 

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I should have worded that a bit differently, it is not unusual for the temp sensor sitting in the head, between two exhaust ports to be 25 - 30 degrees higher.

If you can mount the two sensors in the coolant passage of the intake then you will have an accurate reading of the coolant temp and the fan switch will work correctly.
 

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I have my temp switch in the head, and the gauge sensor in the intake. Fan kicks on at 180 as rated no issues. :)
 

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Discussion Starter #17
dumb question

water temp-gauge …. electric or manual gauge ?

I run a manual gauge under dash - then, I also have a MOON manual read temp gauge mounted in my 'thermostat housing' ( money well spent , liquid filled, large face). My "dash idiot light" did come on once ---
and, I thought I threw a belt ….. stopped checked that Moon Gauge --- read Good --- drove on home.
(but, NO Elect. fan ---- running stock 7 blade direct drive blade , no shroud, 3 row radiator ….. ).
I DO also use and carry my IR temp gun.

Maybe , can you hook up a jumper ground wire (jump around those NPT fittings) … sounds like something simple.
Mine is a mechanical, analog Equus gauge.
I'm not sure if that answers your question.

It's all running like it should now.
I also purchased an Edelbrock carb insulator, which it seems like helped my vapor-lock issues at higher temperatures.
 
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