Ok. this post is gonna be long but i want to share as much info as possible to find the cause of this.
First, i have rebuilt the motor. Starts and runs good cold and hot with no leaks. I have been driving it for almost a month now breaking it in, drove it 1000km's and changed the oil.
Temps seemed normal but after second week had a small coolant leak from water pump. A friend said to use rislone stop leak (bad idea). It DID stop the leak but i noticed temps slowly getting higher and higher. At one point it hit 108c. Strange part is the car was running fine and stopped and started right away again, no i didnt continue to run it at the critical temperature.
So since then until now i have flushed the cooling system twice with distilled water, came out looking like chocolate milk first time. Temps seem better but still hitting 104c at idle which i think is bad?
I have tried to bleed all air from the system by removing the throttle body coolant hose and running the car warm till i see a steady stream of coolant coming out. But the flow seems inconsistant.
What concerns me the most is that even hot there is no coolant flowing back into the resevoir and i assume there should be?
Because of this i have tore apart and checked the thermostat, which looked clean and functioned normally. Then the water pump, which also looked fine and spun normally with no play in it.
Basically im at a loss as to why it overheats while idling. while driving it sits between 93-99c now, but idle it creeps and climbs up to 104c in stop and go traffic.
One more thing to note, i used a thermal gun to check outside temps on radiator and hoses to find hop spots, when engine temp reads 95c the radiator is a constand 30-35c all over. lower coolant hose reads roughly 85c and upper reads 80c.
This leads me to think the CTS is throwing false info maybe? but i dont know how to check that. Any help on this would be hugely appreciated, my head is numb from banging it on the engine lol.
NOTABLE MODS
Atkins rotary apex seals and seal kit used.
Mishimoto aftermarket thermostat installed.
Decat mid pipe installed.
New 2Kw starter motor.
New spark plugs, leading and trailing yes.
New spark plug wires/coils (coils are factory ones but new with no misfires).
DELETED PARTS
Cat converter
Secondary air pump (since cat is gone)
A/C compressor, along with condenser and tubing (compressor was seized when i bought the car).
Any help would be huge, again sorry for long post but i have done a lot to this car and the more info the better. Hope someone can help.

 

if it only overheats while stationary it's more than likely your fans....
also make sure that the plastic under tray and radiator foam is installed correctly

 

Ok there's no foam around the rad. The when I pulled the engine before rebuilding it there was a small piece half hanging from the bottom of the rad it got ripped off. And I didn't have an under tray when I got it. But what exactly does foam on the rad do?

 

The under tray and foam help force the air through the rad.
Also with the car off try and spin both fans, you should be able to feel any dirt/grime/resistance in them. And another easy test for the fans is to turn the AC on, both should be spinning.
However spinning fans doesn't mean they are up to snuff.

 

Ok I'll get around to making an under tray maybe next week. As far as foam what can I use to attach to it as replacement foam? And I've checked at max temp the fans spin but maybe they aren't spinning fast enough? I'll check them by hand later today though.

 

Alright I tried turning them by hand and they feel buttery smooth. After running I also hear and see them both turn on low speed at 97c. And high at 101c. But my problem isn't while moving the rad is cool already it's when I'm idling or sitting still the temperature slowly climbs and creeps. Perhaps there's still an airlock in the cooling system? Does anyone know the proper way to bleed/burb this car?

 

At speed the car moves air through the rad by plowing through it, but at idle the fans have to pull it through. So if your problems are at idle and NOT at speed, the problem is very likely the fans. That's the only variable.

 

Yeah i suppose that makes sense. ill have to find a way to read the rpm of the fans and see if maybe they just arent spinning fast enough then. Btw thanks again guys for the help. It sucks to have come this far with a project and to have a rotary held back by heat lol.

 

Check that BOTH fans are turning, that's probably easier than measuring their rpm. Even at poor rpm they should be able to handle an idling engine unless you're in death valley or something. If one is jammed or burnt out, that'll certainly do it.

 

For what it's worth my 05 is almost totally stock as far as the cooling system goes and it runs at around the numbers you are posting. Not ideal but at stock I don't know if it can be lowered a ton. Almost stock because I haven't replaced coolant yet, so I can't verify if that is up to spec or old or what not. 72k miles I've owned it for about 6k.
My temps are coolant temps read from a bluetooth obd2 tool.
Recently I've started monitoring them a lot more closely because I hit 230f after an extended idle during a high heat day in socal, ambient was 115f.

What I've seen is...
Cruising speeds 190-206 depending on engine load, incline and acceleration.
City driving with a lot of stop and go seems to heat soak my engine and stick the temps to closer to 220f. I do think that heat soaking plays a big role in city driving average temps and coolant temp spikes.

Ambient temps for my readings are usually from 90-100f, so cal weather stuffs so night are no problem.

My temps are worrying me enough that I'm looking into a koyo rad, maybe a mishimoto fan and shroud, and I already had a fan mod incoming to kick the fans on sooner. I've read a lot of stuff about the not great cooling at stock, so.... sucks but maybe worth it for engine health.

One odd thing about what you described though, and correct me if I'm wrong cause I'm far from an expert, but shouldn't the radiator be hotter than 30c you read if it's doing it's job? 30c seems kind like its not exchanging heat very well or couldn't be if it's cooler than what might be ambient depending on your weather (flow or blockage issues)? I'd believe a 85c external hose temp, cause insulation of the rubber.

 

I was having a lot of headaches because of the overheating man I really couldn’t drive with calm like a normal person for long time. Always looking at that gauge waiting for the moment 😁. Well after all I just needed to change the RADIATOR. Many flushes I did to the whole cooling system. The first times lots of corrosion coming out Later looked clean but still overheating especially when idling at red lights and going on the express. Not completely sure what could be yours (maybe the fans aren’t spinning good as mentioned but you just said It Chocolate Milk was your coolant during probably a decade) I just recommend you to change the radiator Your engine is practically new Water seals can be easily blown with that issue :/ It will be a completely loss of time and money. I got the cheap one from eBay (60 bucks) and the problem disappeared If you want expensive Mishimoto go ahead Obviously It is much better but cheap is keeping It cold.

 

I'd guess his radiator is clogged as well, rust colored coolant, plus low surface temps on radiator.

Just as another reference point, over the weekend I did 2 things.

-Changed coolant from 50/50 to 25/75 coolant/water + 2/3 bottle of water wetter.
-Installed the rx8performance fan temp mod to kick fans on sooner.

Idle temps at 92f ambient were at 185 fairly consistently. Fans are on a lot but still cycle accordingly

Cruising temps were ~190 at a similar ambient. So cal doesn't see snow so I should be covered year round, wetter and 25% coolant hopefully covers my pump lubrication and corrosion. We shall see.