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Old Nov 11, 2009 | 12:12 PM
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Question thermoswitch

Hi,

Last weekend I was trying to change the FD3S thermoswitch with FC one. But when I get to the place where thermoswitch should be I find this sensor...





It has two pins where the FC thermoswitch has only one. So I am thinking is this the thermoswitch.... or where it is?

If someone know what is this sensor for... maybe the coolant level?



Can someone help me out? Where is the thermoswitch.... or what sensor I have on the first two pictures?

I am confused.

And to be clear I have FD3S 99`... Japan one.

Thanks!
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Old Nov 11, 2009 | 12:23 PM
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It's on the back of the waterpump housing:



Bottom sensor.
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Old Nov 11, 2009 | 12:30 PM
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So it is beneath that sensor I show on the first and second picture.
How the hell I am going to get to it in the car... it is so tight....

Do you probably know what is that sensor (green circle)?
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Old Nov 11, 2009 | 12:39 PM
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The one on the front on the thermostat cover is the coolant level sensor.
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Old Nov 11, 2009 | 01:23 PM
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Originally Posted by ACCR
So it is beneath that sensor I show on the first and second picture.
How the hell I am going to get to it in the car... it is so tight....
You'll need to remove the alternator to access it. It's still tight, but do-able. The alternator mounting 'ears' can be pretty tight, especially if it's never been removed. Just be careful where you pry. And a plastic dead-blow hammer is handy for re-installing.
Originally Posted by DaleClark
It was a little bit of work to install. I removed the crossover pipe and alternator, then had access. Unplugged the old switch (you have to hunt for the "button" to unlatch the connector - it was on the under side of mine), used a 17mm closed-end wrench to break it loose, then unscrewed it. Some water was lost, but it was just water in the top of the thermostat housing. Put a little oil on the O-ring on the new switch (came with the switch, and it was already on there) and screwed it in. Plugged everything back together, put the car back together, good to go. Pulling the alternator was the most time consuming part - it's a little tricky to get out of there.
And Mahjik, I gotta ask...how do you constantly come up with those pictures?
Should we be concerned?
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Old Nov 11, 2009 | 01:39 PM
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Originally Posted by Sgtblue
And Mahjik, I gotta ask...how do you constantly come up with those pictures?
Should we be concerned?
like I said in the other thread he has the index of the entire forum in his head. and he has all answers ...

anyway I also just did the thermoswitch last week. I swapped with pettit racing one it was the best mod ever. my car's engine now run much cooler. yes the alternator, compression elbow need to go out for easy access to the back of the water pump housing.
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Old Nov 13, 2009 | 12:22 AM
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It's all in the tools.......no way to get a deep socket down there. A flat wrench worked for me. Once the alternator comes out it's not bad at all...and I was just like you. "How the flip am I going to get to that?"

Have fun!
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Old Dec 7, 2009 | 12:30 AM
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Originally Posted by Zoolander
It's all in the tools.......no way to get a deep socket down there. A flat wrench worked for me. Once the alternator comes out it's not bad at all...and I was just like you. "How the flip am I going to get to that?"

Have fun!
Have the alternator out. What is a flat wrench? I swear, no matter how many tools I get, I never have the ones I end up needing. BAAAHHHHH!
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Old Dec 7, 2009 | 12:50 AM
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It looks like a 17mm maybe. Can someone please verify?

EDIT *** Nevermind, I got it with a closed end 17mm***
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Old Dec 7, 2009 | 01:16 AM
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if you had a pfc you could of just lowered the temp when they come on.. just find someone with a datalogit to do it.
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Old Dec 7, 2009 | 01:49 AM
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I think that only works to trigger low speed ON, which I already have done. I am going follow Arghx's instructions to rig mine up to kick to high speed when temps reach thermoswitch level. Here are the relevant postings: https://www.rx7club.com/showthread.p...24#post9657524
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Old Dec 7, 2009 | 10:32 AM
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^ it's also posted here: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/why-engine-so-damn-complicated-part-3-cooling-fan-controls-876767/ . i corrected the listed thermoswitch temp
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Old May 17, 2010 | 03:56 PM
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Hi guys,

Last week I change my cooling liquid and once again I was trying to change my thermoswitch.

I remove the alternator to have the access to the thermo switch, but I find out that I don’t have one. This is strange…. I have a 1999 imported from Japan and I also looked to the EPC and there isn’t anyone. Except the sensor on the picture below… is this a thermo switch?



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Old May 17, 2010 | 04:32 PM
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Unfamiliar with 99 models. On our pre-95 North American models, that would be the coolant temperature sensor...NOT the thermoswitch for the fans.
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Old May 18, 2010 | 02:18 AM
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I can agree with you that this is probably a water temperature sensor.... the part number is B593-18-840A, if anyone can look what it is... I dont understand Japanese. =)

But where the hell is the thermo switch... Do I got one?
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Old Nov 2, 2025 | 01:35 PM
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Originally Posted by ACCR
I can agree with you that this is probably a water temperature sensor.... the part number is B593-18-840A, if anyone can look what it is... I dont understand Japanese. =)

But where the hell is the thermo switch... Do I got one?
did you figure out where the thermo sensor is on the later spec cars or if there even is one?!
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Old Nov 3, 2025 | 08:39 AM
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It does not exist in the later cars



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Old Nov 4, 2025 | 12:37 PM
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From: https://www2.mazda.com/en/100th/
here is a comparison of early vs late

i believe other than that they are the same
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