Installing coolant temp gauge in Miata...sandwich plate or upper rad hose adapter?

Hi everyone. I have an Innovate MTX-D coolant temp gauge on order so I can monitor my coolant temps more accurately when turbo'd. I have found two options for tapping into the stream of hot coolant in order to get a temperature reading. One is the Mishimoto water temp sensor adapter that taps into the upper radiator hose, and the other is the Maruha sandwich plate that goes where the thermostat housing is. With the Maruha I would need an adapter for the threads since it use a 1/8" PT and not NPT. I do plan on a coolant reroute in the future. I was just wondering, which of these two options would give me a better and more accurate reading? Is one better than the other, or are they both pretty much the same?

https://www.mishimoto.com/mishimoto-32-mm-water-hose-connector.html

http://miataroadster.com/maruha-motors/maruha-motors-coolant-temperature-sensor-sandwich-plates/g-66269.aspx

The experts will be here shortly; that doesn't include me.

My comment is that if you're going to turbo it, you should consider doing a coolant bypass that moves the coolant outflow to the back of the engine.

Your thermostat would then be on the back of the engine as well, and the replacement thermostat housing will probably have a fitting for your sensor.

Most of the coolant reroutes do indeed have fittings for coolant temp sensors.

I would not use the adaptor in the upper radiator hose as that measures coolant temp after the thermostat. That's not hugely useful when you have a stuck thermostat, for example.

If you're not looking at a reroute and you're based in the US, Garage Star has a similar adapter to the Maruha motors one, but IIRC considerably cheaper.

Floating Doc (Forum Supporter) said:

The experts will be here shortly; that doesn't include me.

My comment is that if you're going to turbo it, you should consider doing a coolant bypass that moves the coolant outflow to the back of the engine.

Your thermostat would then be on the back of the engine as well, and the replacement thermostat housing will probably have a fitting for your sensor.

Thanks! I actually am considering a coolant reroute, so good to know they have fittings. Maybe I should hold off until I get the reroute kit. 

BoxheadTim (Forum Supporter) said:

Most of the coolant reroutes do indeed have fittings for coolant temp sensors.

 

I would not use the adaptor in the upper radiator hose as that measures coolant temp after the thermostat. That's not hugely useful when you have a stuck thermostat, for example.

If you're not looking at a reroute and you're based in the US, Garage Star has a similar adapter to the Maruha motors one, but IIRC considerably cheaper.

Sounds good, thank you! I did look at the Garage Star one, but it seems to be out of stock everywhere (and apparently has been for a very long time). I do plan on doing a coolant reorute, so I will hold off on installing the gauge until then. Any particular reroute you recommend, or are they all basically the same? I also have a 2001...does that make any difference in the need for a reroute? I've been reading conflicting info due to the head gasket.

If you are looking at reroutes and a turbocharger, there is only one that has taken the turbo coolant into consideration.

Keith Tanner said:

If you are looking at reroutes and a turbocharger, there is only one that has taken the turbo coolant into consideration.

The FM one is the one I was considering actually. Although, after reading about reroutes on 01-05 cars, I'm kind of thinking it wouldn't be worth it. Most places I have read seem to say that with a 01, you would have to change the head gasket to the 99/00 head gasket, or the front cylinders would run hotter than the rear due to the head gasket change. What would your take be on this?

We recommend matching the head gasket to the head. There are changes in the castings.

In reply to Keith Tanner :

Thanks! Have you guys seen any issues on NB2 miatas with the front cylinders running hotter due to a reroute?

I believe we did a video on cooling system theory and another on reroute development. I was not involved in that R&D project.

Keith Tanner said:

I believe we did a video on cooling system theory and another on reroute development. I was not involved in that R&D project.

Cool thanks, I'll find the video.

I had a Maruha sandwich plate in my NA turbo, and I wouldn't do it again. I was never able to get it to stop seeping coolant.

Turboeric said:

I had a Maruha sandwich plate in my NA turbo, and I wouldn't do it again. I was never able to get it to stop seeping coolant.

Gotcha, thanks! What would you recommend instead of that?

On my 1.6 race car , I use one of these on the hose coming out of the back of the head

https://www.advanced-autosports.com/collections/gauges/products/adapter-small

amg_rx7 (Forum Supporter) said:

On my 1.6 race car , I use one of these on the hose coming out of the back of the head

https://www.advanced-autosports.com/collections/gauges/products/adapter-small

Oh nice thanks! And it fits pretty well in the heater core hose? I'm guessing my 1.8 has the same diameter hose back there. Did you hose clamp it down, or use another method?

I believe so but never checked. 

Yes. Good hose clamps. 

I think 5xracing has a similar part but couldn’t find it 

I've got the "same thing" as amg_rx7, and I was coming into recommend it.  Seems to work well. 

Mine isn't red, though, maybe it's the same thing from someone else?  Either way, for $36, Advanced's looks like a nice bit o' kit :)

Thanks guys! I think thats what I will go with. I'm sure I will have to drain the coolant to do this. Bummer, I just put new coolant in! How do you burp the heater hoses, or is it just the same procedure as when doing a coolant flush?