Flyin Miata Coolant Reroute Heatsoaking Temp Sensor???
 

Hey all, long time lurker first time posting since I haven't seen anything on this topic. I recently installed a FM coolant reroute kit on my car (NA6 car with pretty much a full Kraken kit with GT2560R). I noticed since the install if I shut off the car, go do something and come back my water temp has read around 230F upon turning the car back on. I'm reading temp through MS with my laptop since I don't have a water temp gauge yet. Now I never paid too much attention to this before the reroute, but I would have noticed if it even went over 205 or so, so I know this is a new occurrence. I have a theory that the hot coolant from the turbo is heatsoaking the sensor/reroute housing but don't know how to test it. I want to know if anyone has experienced this. Beforehand, my turbo feed and drain were coming from the water neck and down to the mixing manifold. Now since installing the reroute and deleting the water neck, the water lines are routed with FMs turbo connection kit for the reroute exactly as instructed. Turbo feed coming from the bottom port and turbo drain going into the top port of the two turbo ports on the reroute housing. My theory is that now since the drain is immediately meeting up with the reroute housing where the temp sensor is, it is heatsoaking that area causing a false high reading of coolant temp. Especially with thermo-siphoning of the coolant upon shutdown, it is slowly bringing all of the hot ass coolant from the turbo to the housing. I want to confirm that this is happening and not my engine wanting to blow upon shutdown.

I would expect what you are seeing. Certainly FM can tell you what they have experienced.

DNM

I called FM and they said they haven't looked for/ tested for this but my theory makes sense to them. I just wish I could test somehow for the assurance. It's also weird that there's nothing on the internet for this.

It is normal and your engine will not blowup while it is turned off. Every engine does this to some extent for a short period after being shut off. The engine is the source of the heat and is always hotter than the coolant. When you shut off the engine there is still heat transfer which equalizes the temperature of the standing coolant and engine components.

My MS3 tuner noticed this immediately in the first set of logs. I wasn't sure if he had tuned a car with the FM reroute kit so I emailed a picture showing the FM reroute block. I used MS Paint to circle the barbed fitting to which the turbo coolant outlet hose attached. In my car the heat siphoning is audible for a few minutes of minor gurgling. I burped the system again using the bleed screw on top because his first thought was that there was air in the system allowing CLT to rise. By the third revision we came to the same conclusion because CLT drops quickly as soon as the engine cranks over and coolant flows again.

Thank you so much, this is exactly what I wanted to hear. Logically this makes sense but again wasn't too sure and didn't wanna drive my car at all. At first I also thought the gurgling was from air in the system but proceeded to bleed again and came to the same conclusion after contacting FM about it as well. I did come up with a way to test my heatsoaking theory by taking feed and drain from other sources then looping the fittings from the reroute but didn't wanna do all of that if I didnt have to. Appreciate you responding, I knew I couldn't be the only one to experience this.

I noticed this as well with my FM coolant reroute w/ turbo connection. Totally normal. My tuner (Shane at AIM) suspected the same thing. It's a little scary when downloading a log and seeing the temps climb to 230f on shutdown, but yeah once turned back on they very quickly drop.

Glad to see FM also suspects this to be the case.