Hot Water Temps
 

Hi all, I've been getting hot water temps. I'm getting 90C in normal city driving(shifting at 3 - 3.5K rpms) and water temps going up to 99/100C when I start really going up in the rpms but go down back to 90C when I start driving a little more conservative.
the 100C water temps are a little worrying. I've been thinking of installing the FC thermoswitch and making the fans kick in earlier in the pfc settings. is 100C too hot or am I ok for now?

I would add an 180 °F thermostat too. 100°C it is on the hight side. Is the vehicle stock ? Do you have any sort of ducting for your rad?

No, it isn't stock. I have a Koyo Radiator installed but no ducting.

Unless your ambient temperature is really high this time of year in CA., then I agree, your engine coolant temperatures are high. I disagree that a lower temp T-stat would help. The S5 switch and/or changing the fan threshold temperature is fine to give you some cushion in hot weather, but in your case that sounds like it's just treating the symptom, not the sickness.

*Make sure you have a belly pan in place.
*Make sure your coolant level is full and your system is tight with no leaks. A good hint to me that this is the case is when you remove the filler cap on a COMPLETELY COOL engine the cap is held on by just a little light suction/vacuum. And when you break the seal, the fluid level in the neck drops just a few mm.
*Do NOT use anything more than 50% coolant to distilled water ratio. If you can get away with a little more distilled water to coolant that's fine.
*Make sure the face of the radiator is clean of debris, leaves, bugs and slow animals. Same for the face of the AC condenser.
*Clean and straighten any bent fins on the face of your oil cooler(s)
*Make sure you have a belly pan in place.
*Find a place that sells upholstery foam. Buy a half-yard of it...black is probably preferred. Then look thru then nose of the bumper and cut and stuff pieces of it around any gaps you see around the radiator and intercooler ducting.
Oh and make sure you have a belly pan in place.

You need ducting, thats all.

I finally burped the cooling system and I had quite a bit of air bubbles. I also looked for the belly pan/undertray & its missing so I'm going to look for one. thanks for the replies.

BINGO !!

Without air undertray, all the incoming air bypasses the radiator.

Having air in your system doesn't help either

Do not drive it until you source an undertray (i believe you can still get them from Mazda)

Not saying this IS the problem, but check and make sure both fans are working. Only one of mine was working, the one on the AST/battery tray side was not and isn’t really noticeable unless you really look. I only found this out when I went to change the thermostat switch to the FC one. I replaced with rx8 fans because they were 50$ for both fans and motor lol I have a stock motor with Koyo rad, fc thermostat switch, ast delete and no undertray (one on the way) but my motor doesn’t seem to even get close to running hot

I’d bet it IS close to running hot...just like the OP.
Why anyone would knowingly drive the car without one is a source of wonder.

Doesnt seem like it 🤷🏻*♂️ Before the changes I could hear the coolant boiling, I don’t now. I don’t disagree though, one should have an under-tray which is why it was ordered and I’m waiting on it. Not gonna let that stop me from taking it out for short drives tho!