Megasquirt and Innovate Coolant Temp Gauge Reading Differences?
 

Hi guys. I just installed a Supermiata coolant reroute onto my NB2, and set Megasquirt to run the cooling fans at 205 degrees F, then shut off at 195 degrees. I'm using the thermostat that came with the Supermiata reroute. I burped what I think is all of the air, and decided to try and get the cooling fan to kick on again after the new settings in MS. As the car was idling, I noticed the temp gauge went all the way up to 210 degrees F without the fan kicking on. Now, I know the Megasquirt is reading from the stock temp sensor which is also installed in the reroute. I decided to open up MS and see what temp it was reading while my Innovate gauge was reading 210; the MS showed 190 degrees F.

Is there a reason for this variation, and is there something I can do to get them to read a similar temp? 10 degrees is quite a large difference in the two readings. Is this because the Innovate temp sensor is located in the auxiliary port on the heater core end, while the stock temp sensor is located on the other end of the reroute?

Is it the case that you have the innovate gauge feeding it's data to the megasquirt? If so, did you calibrate the gauge in tunerstudio?

I actually do not have the innovate gauge feeding its data to the megasquirt; Is this possible even though the innovate uses its own temp sensor?

I was under the impression that NB2s didn't need the reroute as they use a different head gasket.

From the Supermiata tech docs, they say it is okay to run it on the NB2 with the redesigned head gasket. I got it for a little extra cooling and the ability to use the aftermarket coolant gauge as well. Just not sure about why I’m getting a different reading from the stock sensor that the MS is reading from vs. the Innovate sensor.

I am going to need to see a picture on where the innovate sensor is located and how you are collecting your data.

https://cimg5.ibsrv.net/gimg/www.mia...38a7bf73d.jpeg
Innovate Coolant Temp Sensor - heater core side of reroute. There were no other ports where my sensor fit, so I threaded it in there.
https://cimg6.ibsrv.net/gimg/www.mia...eeed1d949.jpeg
Hard to see, but this is the stock coolant temp sensor that the megasquirt is reading from; on the water outlet end of the reroute.

I have exactly this with my Speedhut coolant sensor. It would read exactly the same in warmup till it reached 85-90c and then starts reading higher than the ECU sensor by about 5-6c
I ended up using a resistor (about 12ohm I think) in the Speedhut sensor wire to bring it into spec. The gauge now shows cooler by 5c during warmup compared to the ECU sensor but once it gets to the critical area (80-110c) it reads bang on the same.
I have mine mounted in the same place as you on the Supermiata reroute. All grounds are mint plus this was the same before the reroute (Speedhut sensor on front of motor, ECU sensor in stock spot) so I rule the reroute out as being a factor.
So either the calibration everyone is using for the ECU is off or the gauge is out. I watch the ECU temp when warming up to burp the system and the thermostat opens right on 88-90c (big burp of air and bubbles) so I say the ECU calibration is correct.

Thanks! Did you follow a writeup for which wire on the sensor to add the resistor to? My gauge is getting power from and grounded to the cigarette lighter wiring, so I believe my ground should be fine as well.

You want it in the earth wire between the gauge and the sensor itself (I assume the innovate sensor is a 2 wire?). You could use a variable pot to dial in the difference and then put that value resistor inline, but for the price of reistors I just picked up a handful of different ones and experimented.
Be aware though, since temp sensors arent linear, adding a resistor will effect the reading across the entire sensor range which is why I'm seeing slightly lower than correct temps betwen 50-80c however, it is dead accurate now between 80-110c where it readlly matters (I think I let it idle up to 115 and was within 1c). Mine will read lower than correct above 120c but I don't plan to ever let my engine get that hot. (ECU engine protection will shut it down before it gets that hot).
Your innovate gauge may be wildly different, so do your own testing and use caution, especially in the upper range where yours may read lower than actual, but for a couple $$ its cheap and easy to test. Always have tuner studio open so you can see ECU temps while testing.

My AEM gauge, placed in the same manner, reads 6-8 degrees cooler than the MS. I calibrated it and checked the grounds. I've written it off as a glitch that I just have to account for.

Thanks guys! I’ll look into the resistor idea. I did notice my values for the CLT sensor in Megasquirt are slightly off what the defaults are in the documentation for the MSPNP Pro settings on a 01-05 Miata, so I’ll change those first to see if it makes a difference.

So I set the CLT settings to what it says in the MSPNP Pro documentation, and now I'm getting a variation of 3-5 degrees Fahrenheit, which I can live with. I did notice however that when first turning on the heater, there is a blast of cold air before it becomes warm. Also, the temps climb slowly while at idle RPM with the fan running, but when I give it some throttle, the temps start to drop. I'm guessing this means I still have some air in the system and need to burp some more? Any tips on burping all the air out of the reroute? Burping this thing has been a royal pain because the Lisle funnel adapters do not fit in my Koyo radiator.

Thermistors are not linear at all, they have a curve. Adding a fixed resistance does not offset the entire range linearly. For example, 30C is ~2200 ohms, 100c is ~180 ohms on a GM thermistor. That's roughly 0.4% low while cold or more than 6% low while it's hot.