Are you overfilling it? It's an expansion tank. The coolant level goes up by approximately 1 inch when hot. Don't fill it up all the way. Keep it at the F (Full) level when the engine is COLD. If the coolant level is at the F mark when the engine is cold, it should be about an inch higher than the F mark when the engine is hot.

Regarding the blown coolant seal theory, do you get white smoke from the exhaust when starting it in the morning? That's a dead giveaway. If you don't, the easiest way to test for an internal coolant leak is, like you said, to do a coolant system pressure test. See if the pressure drops.

With that said, RX-8s have a weak cooling system. A lot of these cars overheat on the track.

Good luck and keep us posted!

 

I rented the Advance Autoparts cooling system pressure tester. My system seemed to hold pressure when I pumped it to ~10psi, and my cap seemed to hold pressure when I pumped it to ~13 psi.


Would coolant start to vent past the radiator cap, even when the needle hasn't moved past 12-oclock? I'm going to either get a an aftermarket water temperature gauge or a scangauge to measure my temps while on track.

 

Coolant is at "L" when cold, and just above "F" when hot, so it's not overfilled.


I do not get smoke from the exhaust.

 

12 o'clock is 237f. So yes it could.

Did you do the test with the engine hot and cold?

 

This is something that everyone who tracks their car should do.
You want to monitor a few areas.

 

If it's at "L" then your coolant level is low. Fill it up to the "F" line. Half an inch above the "F" is perfect.

 

poo;4735053]12 o'clock is 237f. So yes it could.

Did you do the test with the engine hot and cold?[/QUOTE]

Yes.

No bubbles when cold.

Some bubbles when fans are cycling on/off (engine hot with cap off).

 

Adding a thorough amount of radiator ducting foam has eliminated the boil-over due to improved cooling. however, I suspect I'm still running hot so I will improve the sagging undertray and run a higher percentage of water and see if that helps.

 

Get a Bluetooth OBD2 adapter off eBay and monitor your temps. That will tell you for sure if you're running hot or not.

 

Running a higher percentage of water will cause it to boil sooner. Ask me how I know.

 

Or dump that coolant altogether and go waterless: Evans waterless coolant, prevent engine overheating

 

How can it boil sooner? Coolant is only used to stop the liquid from freezing. Not boiling. The system is pressurized to stop it from boiling.

 

The ratio of antifreeze to water in the coolant effects the boiling point of the coolant.

 

Derp.

 

I run Evans, it works very well. The only downside to it is getting it, so you always have to have extra on hand or reuse what you drain out if you are working on something.

 

i plan on adding oil and water temp gauges to confirm the actual temps (and oil pressure, of course).

 

Extremely good foam sealing, using a zip tie to prevent undertray sag, and a 70% water solution seems to have solved my cooling issues. Thanks all!

 

Glad it worked and many thanks for updating us. What are the temps?

 

my data logger works through a laptop so I can't use that on the track. real gauge set is next. but I am seeing 200F after several hard 2nd/3rd gear pulls without cooldown.

 

Something else worth considering is backflushing the radiator fins. I find that this car's radiator and condenser collect a lot of junk that needs to be washed out every once in a while.

 

Im having a similar problem too and i found a blockage in one of my fans. I don't know how long its been there. Both of my fans don't turn on at all. If one fan is blocked will the other fan still turn on? I replaced the fuse already. Are the motors to the fans individual? Should i replace my entire assembly?

 

Yes they have individual motors. Yes if one fan is blocked, the other will still turn on. I'm guessing one of the rubber grommets from the air filter box tray dropped through the hole and jammed the fan. They're right above the fan blades. You don't need to replace the whole fan assembly but you might have to replace the fan motors. First check if they're getting power. Check the fan relays. If they work, directly give power to the fans and see if they spin. If they don't, time for a new motor.

 

At one point I had a fan issue where it appeared and acted like a stuck fan, but turned out to be a brush inside the motor that became unseated and stopped the fan from turning properly or passing current.

The fan setup is kind of interesting so if the passenger side fan is damaged neither fan will come on until the high speed mode is engaged (which, in the case of a bad passenger side fan still only turns on the driver's side fan).

 

Nah I had these dirt wasp things build a nest and it stopped the driver side fan from spinning. But the passenger side won't turn on either even though it appeared to be free spinning and moved when I spun it by hand. That's why I was asking if one is stuck will it stop the other. How do I test to see if power is getting to the fan motors?

 

Jump the fan relays. You test the fans by directly wiring them to the battery. Don't worry about the polarity. It's not a problem.