Race cars have numerous systems that must be monitored. One of the most basic is the water temperature. While my Spec E30 has its stock temp gauge intact, I wanted something a little more accurate and reliable than the blue, black, red sequence of my stock gauge – what most call a dummy gauge or idiot lights. I know this isn’t rocket science, but I can tell you there are a lot of people out there still running idiot lights, so maybe this will motivate them to add this little piece of security.
For this application, I chose the Autometer 2-1/16 inch, 100-250 degree, Air-Core, Ultra-Lite (pn 4337) Water Temp Gauge for its reputation and affordability. It will give me a reliable understanding of how hot my motor is running. What it does not do, is to tell you when you’ve sprung a leak and run the car out of water. For that, I’ll be installing a pressure switch and warning light, which I’ll detail in another article.
Now to devise my plan. The gauge needs three things to work properly: First, is a fused 12V power source. Second, it needs a signal from the sender, and finally a good ground. Before wiring the gauge, I need to find a place to mount the sender. Having researched a number of alternative installation points, I decide to mount it in one of two covered ports in the thermostat housing.
Neither of the adapters that came in the package fit into the threaded ports in the thermostat housing. Rather than buying an adapter, I decide to tap the original nut. In this case, the threads on the sender are 1/8 NPT (National Pipe Thread), and I found a tap and drill bit that would work nicely for it.
Now that the tedious part is done, I prepared the gauge and sender for wiring.
The power and ground wires will be hooked up under the dashboard. I know generally where I will mount the gauge and where I will source power and ground from, so I cut the right length of wire, about 18 inches each. For the gauge end of the wire, I found the correct size connector, stripped the end of the wire, ran a piece of heat-shrink tubing over it, and crimp the connector on. A little heat from a lighter shrinks the tubing snug and now my connector was ready. I installed circular connectors for the other ends in the same way, with heat-shrink tubing to insulate both ends of the wire. I used circular connectors on these ends as I know they will be screwed down.
With connectors ready, I moved to finish my work under the hood.
First, I ran a long wire through the firewall and back under the dashboard. This wire will go from the gauge to the sender. I make my life a little easier by running a longer wire than I’ll need, which I can cut to fit once everything is mocked up.
Once I start mounting it along the engine bay I can cut it to the correct length to reach the sender. For this picture I’ve simply stretched the wiring out across the engine bay so it’s easy to view.
I run that wiring along the sections of engine bay looking for places to zip tie it the existing loom. Once it’s pretty much mocked up I cut the wiring just a little longer than I need to reach the sender. You can take up some of the slack later, but it’s better than being too short and having to solder two wires together.
To connect to the sender, I used a circular connector. The sender has a threaded post that has two nuts sandwiching a crush washer. Remove the top nut, put on the connector, replace the nut and snug it all down. Here you can see it the whole enchilada installed back into the thermostat housing.
Now to mount the gauge.
Luckily I have a spare gauge panel left over from another project car, so this will save me some time in cutting and shaping a mounting plate for the cockpit. I choose a mounting location that is easily visible, but out of the way. In this case, the space previously occupied by the radio and HVAC controls.
I zip-tied the plate into the basic location and started to mount it.
For the bottom side, I mocked up a mount using soft steel bar, which I drilled and riveted into the plate on one end. The other end was already drilled and ready to be mounted on a nut and bolt that I already created for another switch plate. Full disclosure, I first tried to JB Weld it into place, but it wasn’t curing how I wanted, mostly due to lack of prep on my part. So, I went with the old rivet gun and it worked perfectly.
With the bottom mount finished, I used an existing tab on the side of the panel to screw it into the dashboard. The panel is tightly held in place and rattle free, so there’s no need to over engineer.
Time to do my final assembly.
For power, I used the wiring going into the start button from the ignition switch. I knew it was fused, as the main power comes from the fuse box. I routed the ground wire to the same terminal as other grounds for my helmet air and cool suit, but you just need to make sure it is secured to the body, firewall, or anything secured to them.
Now that all the hard work was done, I could install the gauge. I started by running all my wires to the gauge through the gauge bracket and through the front of the panel. I connected all the wires to the back of the gauge — each electrode is marked clearly — and made sure they secure. I installed the wired gauge into the panel and tightened everything down from the backside. The finished product is…well, usable if not gorgeous. The final step was to fire up the car and watch the needle to make sure it worked as it should.
The gauge panel will be used for other gauges such as Voltage and Oil Temp in the near future, so having the extra space is great. It’s ugly, but it works, and this made me realize I need to spend some time tidying up the interior and dash. Time to go buy more sheet metal!