Now you're talking my language! An Arduino or RPI would be awesome for a simple data display. Depending on how well you can code(or can likely find most of the apps you need in repositories), you can get a cheap small ~5-6" touchscreen from ebay or amazon to connect to it and run a stripped down Linux distro to run an info app for a dashboard. Even better than a wheel sensor for the speedo, for probably around ~$15 you can get a GPS module for the RPI and have not only actual speed but can setup turn by turn GPS directions as well. Then with the built in BT capabilities it can send the directions right to earbuds or helmet speakers and also be a media center as well. Overkill? Probably, but cheap and would be fun to work on.
I am working on using an RPI to trigger relays attached to the motherboard pins on remote servers so I can reboot and cold start them automatically from a simple host ping script when they lock up. Also started plans for an Arduino to control the peltier setup on my computer to dynamically adjust the duty cycle based on calculated dew point. I have a controller that does it now, but it won't let me do straight manual duty cycle control. I installed a switch on one line of the thermocouple though to trick it into allowing me to manually set it down to 0c(since it makes it think the dew point is 0c), but I'd like to be able to go below that.
Yeah, a remote hard reboot on a server is definitely great tool in some cases where the server won't respond otherwise, and the function needs to be restored ASAP. I used to do a lot of remote control-systems support for plant equipment. Sometimes, the plant couldn't wait for me to drive an hour or two to them to get something up again before things got dicey or expensive. I usually could guide a human to force the reboot, but automating it where it makes sense and is safe to do is the ticket.
I did control systems - PLCs/DCS/HMI/SCADA/DAQ engineering work before my body broke down a few years ago. LOL, probably from being on call all the damn time! The meds I have to take now and the pain I have cause some frustration with doing technical work that used to be easy for me. But I can still code anything I really need, and the support libraries for arduino and pi are ubiquitous and decent. The possibilities are endless indeed.
Your peltier cooler sounds cool. (but clearly you don't want to let it get too cool, lol. liquid water is no bueno there.) Replacing your controller with an arduino and your own code will be great. BTW, I've used 10K NTC thermistors for easy temp measurements on arduino. I built a crock pot controller for making yogurt and sous vide cooking. And also to pasteurize eggs without cooking them to make safe to eat cookie dough and cake batter for my kids, LOL.
I've worked with thermocouple inputs a lot industrially, but for my CHT, I'm going to try a MAX 6675 module from eBay. Interface is SPI, so I'll need a micro. Total cost of the CHT monitor will be around $10. Maybe a little more depending on how I display it.
I haven't done much raspi or arduino work since my son graduated HS. I used to mentor his robotics team. So, I'm a little rusty, but it'll come back as I need it.
So in my infirm and uncertain retirement situation, I hope to have some fun and share some ideas. I'm not very sharp anymore, but I ain't dead yet either.