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.

 

The temp gauge in the instrument cluster.

 

The bigger sensor is for fan control, yes? Similar to 1.6 miatas only on the rear of the head?

 

...and yes, it threads into "1000j"s loation:



https://www.miataturbo.net/forum/t22463/

 

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.

 

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.

 

Thanks for your help fellas. I guess that means I don't need it as the 94 instrument cluster won't use it! Sweet.

 

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.

 

My 97 is the same way.

 

Which way? (single sensor w/ 3 wires, or two separate sensors?)

 

Separate sensors.

 

Ok, so it's just like all the other NAs out there.

 

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...)