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Old 05-08-2009, 12:31 PM   #1
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Default Water sensor on the back of the head

I'm currently doing a head swap from a 2001 head to my 1.8 94. On the back of the 2001 head where the water temperature sensor is, there is another smaller water temperature sensor there too. Its single wired and goes into the injector wiring loom. Does anyone know what this is for?

My current head has a tapped hole for this but is blanked off with a screw. I want to know what it is for and whether I can leave it out.

You can make it out just about in this picture:



The second sensor is below the water pipe slightly hidden from view by the copper EGR pipe.
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Old 05-08-2009, 01:08 PM   #2
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The temp gauge in the instrument cluster.
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Old 05-08-2009, 01:46 PM   #3
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The bigger sensor is for fan control, yes? Similar to 1.6 miatas only on the rear of the head?
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Old 05-08-2009, 01:51 PM   #4
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Quote:
Originally Posted by Saml01 View Post
The temp gauge in the instrument cluster.
...and yes, it threads into "1000j"s loation:



https://www.miataturbo.net/forum/t22463/
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Old 05-08-2009, 01:59 PM   #5
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Originally Posted by thesnowboarder View Post
The bigger sensor is for fan control, yes? Similar to 1.6 miatas only on the rear of the head?
it has 3 connections, so I'll just leave it at that and await joe perez or braineak to give the real data. It would be sweet if one of those switches to GND because I have a spare.
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Old 05-08-2009, 02:02 PM   #6
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Originally Posted by thesnowboarder View Post
The bigger sensor is for fan control, yes? Similar to 1.6 miatas only on the rear of the head?
The larger sensor feeds the ECU. In all '94+ engines, the cooling fan is controlled by the ECU, so there is no need for the third sensor (actually a thermoswitch) which the 1.6 has on the front thermostat housing.

I honestly never realized that the '01 had a seperate sensor for the dash gauge. I'd thought that all of the NB's used a single sensor with three wires to feed both the ECU and the dash gauge. Learn something new every day.
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Old 05-08-2009, 02:13 PM   #7
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Thanks for your help fellas. I guess that means I don't need it as the 94 instrument cluster won't use it! Sweet.
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Old 05-08-2009, 02:20 PM   #8
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Quote:
Originally Posted by Joe Perez View Post
The larger sensor feeds the ECU. In all '94+ engines, the cooling fan is controlled by the ECU, so there is no need for the third sensor (actually a thermoswitch) which the 1.6 has on the front thermostat housing.

I honestly never realized that the '01 had a seperate sensor for the dash gauge. I'd thought that all of the NB's used a single sensor with three wires to feed both the ECU and the dash gauge. Learn something new every day.
The 99+ motor has one sensor, but it has three electrical connections on the plug. The "1000j" I posted is a plug in the 99-head, and used by the 1.6 instrument cluster.
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Old 05-08-2009, 02:57 PM   #9
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Originally Posted by Joe Perez View Post
I honestly never realized that the '01 had a seperate sensor for the dash gauge. I'd thought that all of the NB's used a single sensor with three wires to feed both the ECU and the dash gauge. Learn something new every day.
My 97 is the same way.
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Old 05-08-2009, 03:15 PM   #10
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My 97 is the same way.
Which way? (single sensor w/ 3 wires, or two separate sensors?)
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Old 05-08-2009, 03:50 PM   #11
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Which way? (single sensor w/ 3 wires, or two separate sensors?)
Separate sensors.
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Old 05-08-2009, 04:01 PM   #12
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Ok, so it's just like all the other NAs out there.
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Old 05-08-2009, 07:36 PM   #13
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Just to clarify this post, I got a little confused earlier between the heads. Yes you are right the sensor needs to be transferred from the old 94 head onto the new 2001 head that i'm installing in order for my temperature gague to work.

(I made a mistake earlier when saying I didn't need it - the first post had a mistake too when i said the 2001 head had the sensor and the 94 didnt, the other way around...)
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