How-To: Linear Water Temp Gauge
 

Ok, so maybe you heard but you can have a very accurate Water Temperature gauge in your car and all at the cost of a couple of resistors. Here is how to do it:


Tools:
Phillips head screw driver (use it to get the gauge out)
Soldering Iron
Solder

Resistors (½ Watt):
137-139 ohm (It is very likely you will need to series or parallel two resistors for this)
6.8 ohm
1k ohm

Recommended:
De-solder wick
Flux

I don't know who did the original fix on the temp gauge, but I used KiwiNB's pics. and text file. I have attached the text, but here is the picture:
https://www.miataforumz.com/attachme...ine=1313451772

Since the picture is pretty descriptive, I will provide you with some key points and how to get there.

Here is the water temp gauge out of the car. The diodes were color coded on my car, you want to mod the one with the black line, not the blue. This may not be the same in every car.
https://www.miataforumz.com/attachme...ine=1313451772

Here are all the solders done. Its pretty hard to say which one you should do first, but start from the outside and do the middle big f'in solder last. I numbered them in the order I found to be best:
-Solder 1: Make sure the relay is in the right orientation (the red thing with blue and black bands). This is the 1k ohm and relay in parallel.
-Solder 2 & 3: are the two series resistors.
-Solder 4: DO NOT gob too much solder on it like in the picture (see ahead).
-Solder 5: Have fun!
https://www.miataforumz.com/attachme...ine=1313451772

Now here is the THIRD solder in more detail. You don't really need to do this, but it may make your life easier. I decided to do a series pair. I suggest using a "hook" method of holding them together. It can be hard to solder two pieces hovering in the air as they may not exactly touch. Avoid that hassle by hooking them like this:
https://www.miataforumz.com/attachme...ine=1313451772

Another pitfall, but this time at solder #4. If you glob solder on it, then the gauge won't be able to screw on very easily. Here is what NOT to do:
https://www.miataforumz.com/attachme...ine=1313451772

Flux and/or desoldering wick are great here also. Here is what you want it to look like:
https://www.miataforumz.com/attachme...ine=1313451772

Do I need to get a how-to remove the gauge cluster going also? I have that one written up, but I figured its simple enough...

I'm guessing not, I wouldn't want someone who didn't know how to remove the gauge cluster to be performing this mod.

Do you know if this works for all models? I notice you have an NB

Well, some people are a bit afraid of pulling on that hood!

But to the important question, I have no idea if it will work on an NA or not. I don't see any reason why it wouldn't. Would you like to try it? Its not permanent and any nastiness left over wouldn't be seen anyway. plus, I get the feeling that once you peek at the gauge it could be obvious from the circuit elements.

Yeah, I'll try it. Pending motivation and time of course, thanks for the write up. I'll report back if/when it happens.

One picture I forgot to post:
https://www.miataforumz.com/attachme...ine=1313462156

Note: I have had some question over the legitimacy of this mod (damn m.netters and their naysaying!! jk). I have a scangauge and I can confirm the needle travel up to 200F. I haven't been able to get it any hotter with my new Rad. so that will have to suffice for now.

Note 2: Please please, realize the prespective is centered on the gauge and not from the driver's position. That may seem obvious...but not everyone connects the dots ;)

Awesome writeup, adding this to my to do list.

OHHHH, I love this, I'm doing it tonight!!

Since you have an NA, please post up your results. preferably with a scangauge reading just to confirm accuracy on the NA cars.

For sure, I had overheating issues last week, I plug megatune to see the temperature et realize the gauge was steady until it went up 210 or so, not really accurate. (at 230F, the needle was at the 3/4)

I'll test it with the megatune gauge and I'll take picture of it whent it will be done, maybe for next week.

I found the willyman writeup for the 90-93, I'm gonna use this as a guideline.