Overheating issue
 

One of the first things I did on my stock 97 is add an aftermarket coolant gauge. I plumbed it in between one of the heater core lines so when the gauge ran a bit hot I didn't think much of it because it wasn't in the same location as the stock CLT. I ran that for a couple years.

Now I have just installed a coolant reroute and a crossflow radiator as part of plans to prepare for boost. The reroute had a port for an external sensor so now the factory clt and my aftermarket temp sensor are right next to each other. It's still reading hot.
At cruising speed it hovers around 205-210f
At idle fans kick on at 220f - all this according to the aftermarket gauge.
When fans kick on it will drop the temp rapidly down to about 205-207 within 30 seconds which is about when they turn off.
I have replaced my stock clt twice now (admittedly before the reroute) and the temps have always been the same.
The car never had an undertray - one is on order now.

This doesn't match with pretty much anyone who is running a reroute on any miata I have read. I don't really want to proceed with my turbo plans until this is resolved. Only thing I have done to troubleshoot was use an infrared thermostat on my hot coolant hose which reads very similar to my aftermarket gauge.

Is it possible that the stock clt on the stock ecu is reading low? Is there any way to calibrate it? The clt sensors I used were generic OEM replacements that match the Mazda part numbers for the 1.8 - but not genuine Mazda

Next step is MS3 and I would like to go into that with at least factory water temps since that will have its own clt calibration from what I have been reading.

You can't *not* run an undertray and complain about your car running hot. Even stock cars will have issues sometimes without the undertray (as yours seems to be), especially when running AC on a hot day. The airflow coming through the rad just isn't all that great.

Get the undertray, then see if the problem persists. You're not running an important oem part so it's not totally unexpected, though I can understand it seeming a bit strange that it's happening on a stock car. Are you running a stock radiator and fans too? What temp thermostat? AC?

I agree it should have the tray and thats why its on the way. What I am mainly concerned is that the fans turn on at 220+f. That should have nothing to do with the tray.
195f thermostat, qmax reroute, supermiata crossflow radiator. 30/70 coolant mix. No AC, stock single fan.

Let us know how it works after you have the under tray installed. Until then, kinda doesn't matter.

IIRC stock thermoswitch closes at 207F. 5% between your gauge, the sensor & the thermoswitch, who knows where the error is.

Since you're running a stock ECU, it should be noted that there are two different sensors located in two different places for temperature sensing for the gauge and for the fans.

Good point. I forgot about that. Gauge and ECU map get their reading from opposite sides of the head. Qmax messes that up.

I am into my 4th beer so forgive me if my post is a bit confusing.

On our race car should we put the dash gauge sensor in the Qmax so, back of the head.