Hello everyone, in my ongoing efforts to lengthen the life of this rotary engine I am currently tackling many things heat related. I have been monitoring my coolant temps with an obd2 scanner and app. As I was overheating while idling early on in ownership of this car I replaced the radiator, thermostat, fan relay mod from rx8performance, and mishimoto fan/shroud (did check that both fans are in a pull config through the rad). 25/75 mix of coolant/distilled w/redline water wetter. These were done about a week ago, not sure how great an impact an improperly bled coolant system has. I did try to bleed the system both using the throttle body coolant hose nipple, which immediately shot out coolant everywhere, which I guess means I didn't have air in it, and by idling and revving with the coolant expansion tank cap off. 72k miles on the car, owned it for ~8k.

Before the parts were installed it generally ran hot, almost a consistent 220 and up. I suspect it was mostly the fan mod that helped with idle temps since they just kick on sooner. California summer temps being 95+

After the new cooling components were installed it manages to idle down at at 190-200 or so depending on external conditions like ambient temp and air flow around the car. But coolant temps still get rather high at 85mph highway speeds, 220-225 on flat 3k rpm highway cruise and will slowly climb in temps on extended inclines. In one test after warm, I did a near redline push on the freeway and the coolant temp shot up from around 210 up to 230 forcing me to backed off and let it settle, took a while.
Still no leaks that I can find, and I haven't had to refill the tank, no power loss or smoke on startup that might suggest coolant seal failure, to me at least. I have tried checking the expansion tank for bubbling while someone revs the engine, but I saw just general liquid turbulence I.

I'm about to take it on another test run to see if maybe it did have air stuck in the system, but based on what I saw I have my doubts.
-Ran another dozen miles or so, nothing changed. If trapped air is causing this, it must be something wicked in there.

I read a lot of people say the undertray and taking advantage of ram air is important for this car to cool, I replaced the undertray with the LBR aluminum one/w uprights since the prev owner lost/wrecked the tray, it does not have the foam around the rad to direct airflow. But does the foam have that great an impact on cooling, to the point where it the radiator is that ineffective at speed if it's missing?

Edit
Is there a specific test I can run to see if the lower hose is collapsing under engine load?

As always, thanks a million for the expertise on this forum, makes DIY possible.

 

I am pretty new here and the rx8 I bought is out of state yet until Jan. However I had collapse on a different car under load and the only way I could see it was to anchor a gopro to watch it. Granted this was years ago, but it did the trick. I have been collecting parts for the rx8 already and have a set of Mishimoto hoses to go on. I just wish I didn't buy them direct because I noticed this just came up last week: https://www.ebay.com/itm/Mishimoto-M...AAAOSwb19fdjQq Could have saved myself a nice chunk of change. Oh well.

Anyway, hope this helps

 

Conduct,

You've done a good deal, and seem to have seen some improvement. I'd recommend:

• flushing the coolant system. (didn't see where you'd done that)
• completely seal around the rad
• change the rad hoses. At 72k mi... if you don't know they've been changed, it's simply worth doing.

All the best.

 

Thanks everyone, the hoses are my next target, and since I'll be in there, I figured why not do the pump so parts are on their way and I can install over the weekend. I did actually flush and fill the coolant, the "old" coolant still looked pretty decent imo, not a lot of debris or cloud to it, but obviously something is amiss with the system and since it was an unknown from the previous owner I figured why not. The more I test and watch temp the more I suspect them too, but then again I suspected the radiator and fans and thermostat so wth do I know. Lol.

The gopro idea is something I'll consider for sure, I have a wireless inspection scope I should be able to zip tie in place and then watch it in real time as I put it through some road testing before I go through with the install of new parts.

Will do the foam too cause I'm already more than half way into replacing almost the entire cooling system so whats 10 bucks worth of foam.

Thanks for the ideas! Will report back once things get resolved, or not just for future owners to potentially search through.

 

Don't overlook the oil cooler thermostats. Install lower temp t-stats in both oil cooler and repacking foam around the radiator has corrected all my coolant temp issues.

INB4 you are told to search

https://www.rx8club.com/series-i-tec...mostat-167731/

 

Interesting read, I am seeing that I should address the coolant system issues first since they handle the bulk of the engine cooling, but as I continue to work on the cars engine temp management it is a def bookmark for my future reading and study. And I guess a possible fault point if the oil cooling system is not working correctly.

Thank you for another possibility as I continue my research.