Basically, this thing:
It's a sandwich plate that goes under the thermostat and has a threaded hole for a temperature sensor. I do happen to like buying parts from Ken, but unfortunately this part has been out of stock for a while and the last time I contacted them, no ETA. I know that there were some JDM manufacturers making these as well, but I've so far been unable to find one.
I have to complete the cooling system overhaul in my NA and didn't want to drain the coolant twice, so I'm somewhat running out of time. I know that one alternative would be to just buy a coolant reroute kit, but I'm trying to hold off on that until I know if my NA needs engine work or not.
WWGRMD do if you don't have the skill or tools to just make one?
Google shows this as an alternative: Maruha Motors coolant temp sandwich plate
They appear to be special order however.
Thanks, that's exactly the style I was looking for. Might have to overnight one from Japan 
.
Although at that price plus shipping, I better make sure my engine isn't partially toasted already.
I drilled and tapped into the thermostat housing.
In reply to BoxheadTim :
I'm a bit surprised there isn't an ebay knockoff of that part. It certainly appears to be simple enough.
Any reason you wouldn't put the sensor in the stock location and just bypass the dash gauge? That's what I'm doing with mine here when I install my AEM gauges here in a few weeks.
I had one of the Maruha sandwich plates on my NA6 turbo, but I could never get it to seal completely - there was always a tiny coolant drip there.
In reply to bmw88rider :
I prefer to have everything stock continue to work as is, supplemented with more more precise gauges that aren't 100% in line of sight.
In reply to FieroReinke :
Should have mentioned this I'm not interested in cutting hoses to put in the sensor. Not to mention that those require a flow of water through the rad, which may or may not be the case.
What year again? And remind me what ECU.
You could get an NB sensor, which combines the ECU and gauge sensors into a single body. That opens up a fitting on the back of the head for your tertiary sensor.
If it's an NA6 like the one in the picture and you're running an aftermarket ECU, the fan thermoswitch is now redundant and you can steal if for your sensor.
If it's a 1996+ car, just tap into the OBD-II system.
Alternately, a spacer like the Garage Star one is not difficult to make if you have access to a drill and a hole saw. The only real important dimensions are the two holes for the bolts and the round hole for the center.
Memory is tickling at me that there's a threaded hole in the block for coolant. Exhaust side down low? You could probably put a sensor in there. Sure, it'll read a bit differently than if it were in the head but what you really need to know is if it's acting normally, and you can figure out normal pretty quickly.
All that said - the factory gauges work fine for me. If it's not moving, you're good. If it's moving, it's time to do something about cooling down. That's really the important thing to know. It's like an idiot light that gives you information on how far and fast you're moving from "normal".
Makes Sense. Just wanted to throw it out there. Most of the are no longer sold because of demand. For not a heck of a lot more the coolant reroute is the go to. Long term, I'll have it on my car too. I just have to figure out some hose routing with the intercooler charge pipe wanting to be in the same spot as the rerouted coolant hose.
In reply to Keith Tanner :
It's an NA6, currently with the factory ECU. Depending on what I find when I dig into the hard starting issue, it may grow either a rebuilt, high compression 1.6 or a VVT 1.8. Obviously neither will run off the stock ECU .
I do like having more precise oil and water temp gauges around, especially as I have a pair that can be set to change colour when the temps exceed a certain threshold.
Easy answer is to just pull the sender for the factory gauge and put yours in there. Or use a resistor to tweak the signal to one of the gauges - should be pretty easy to find out how they both read if you have access to a pot of boiling water and a multimeter.
The car doesn't have an oil temp gauge now, of course, but you can tap that one off the side of the block for sure. Or tee into the oil pressure sender.
Last I heard of the hard starting, we were checking fuel pressures. Yes?
In reply to Keith Tanner :
We will be checking compression and fuel pressure once I've dealt with some work on the E34 daily driver, yes. For some reason the brake job on the E34 has slightly higher priority.
