So this has been happening for some time now, I live in Miami, FL so it can get really hot here. Anyways, the AC is very crucial during this time but something is happening after leaving it on for a while. All of a sudden it starts blowing hot air and the car temp slowly passes the middle. As soon as I see that I turn off the AC and the temperature goes back to normal. I checked the fans and they both work and replaced the relays. Could it be the thermostat, water pump, radiator, not sure.

 

If the needle is moving you are already well beyond the warning zone. An OBD2 dongle will read your water temp if you want to know just how hot you are getting.

I'd start with the thermostat.

 

I've also noticed is doesn't over heat at night? strange...

 

check the congrats thread in my sig.

Looks at the cooling mods, specifically radiator foam.

 

i will check the coolant overflow bottle first, the tab that holds the radiator cap is known to fail(brittle plastic)

its its broken (or soften/about to break off), you WILL overheat

 

So I changed the themostat and it's still doing the same. Should I go for broke and get a bigger fan. The same issue happened in my Camaro and with a little modification, a la bigger fan, there was no more overheat.

 

clean your ac/radiator with a good pressure washer from the front and back( pull your battery and air box to clean the back). then check it for any bent fins. if there are any you can straighten them with some time and a pair of flat tip tweezers. Make sure there is good foam in the sides of the radiator so you are not recirculating hot air.

The ac cuts off when the radiator gets too hot. That is a normal function of the car.

Does your car have a undertray below the radiator?( this is extremely critical)
What year is it?

 

your ac is not rejecting as much heat and the air is probably cooler allowing it to shed heat faster.

 

My rx8 is a 2008, there is a undertray but when i bought the car it was missing a front bumper. i ended buying a after market bumper so there's a few open areas in the front of the car, below. should this matter?

 

Can you post a pic? Normally the tray connects to the bumper but i do not know about aftermarket bumpers.

 

Not the best but I'll upload a video in a bit.

 

Here's the video, hope it will help.

 

the gap is weird, but it looks okay. Clean, straighten and foam

 

Here's another video, see how the car acts with the AC on in the Drive gear (I have the e-brake on). At the 2:20 mark the AC is off. Plus the shaking, does this look normal. I did replace the left motor mount and it doesn't feel that different, i do have the right side so I'll install that later.

 

I can't tell how bad the shaking is, but I'm guessing its the motor mounts. Passenger side normally goes first

 

Well the driver side was really bad, the plastic part in the the middle of the mount was broken off. When I brake the car hard I would feel strong vibration. Since I've already replaced the driver side its much better when I brake.

 

changed the radiator cap, it helped for a day then it over heated again.......

 

should I remove the entire radiator?

 

replacint it wouldn't hurt, but probably doesnt need it.

Have you washed it Directly, with the front bumper off?


Have you checked to make sure the radiator is sealed all the way around? If it isn't seal it.


Have you verified that very little if any of the fins on the radiator are bent? If they are then straighten them.

Replace the thermostat.


Flush the radiator.


Coolant system pressure test.


If that passes, pull the water pump and make sure the impeller is not broken /loose.


Verify the restrictor is in the heater core hose.


Then replace radiator and all coolant hoses. Hoses degrade on the inside and can block flow.

 

Did you fix the issue? Your car seems to be doing EXACTLY what my car did. Overheating in the sun with the AC on. Turning off the AC would drop the temps again. Would never overheat having the AC on at night.

Would love to hear what you did

 

It is a system and it has to be properly diagnosed, read the last post from Logalinipoo.

 

I'm well aware it's a system 9k

I just don't get why anyone on this forum don't talk about how our fans slow down over time. It's a well known issue. Plenty of RX-8s have this issue, they just don't realize it because A) they're not in hot climates or B) they don't monitor their temps.

OP is only overheating at idle, during the day with the AC on. It doesn't happen when moving, or when idling at night with the AC on. Exactly the same problem I had. Isn't it obvious? It's the FANS! The fans only come into play when idling or moving slow. When you're up to speed, the fans turn off because the air hitting the radiator is way more than what the fans can pull. So it's pointless to keep them on.

OP, check your fans!! Sure, they're spinning. But are they spinning fast enough? You can't tell how fast they're spinning just because they're loud. Get a multimeter, connect each fan (individually) direct to the battery and see how many amps they're pulling. Compare them with the numbers in the pic I posted. Bet you they're not pulling these amps.

DO NOT clean the radiator with a pressure washer. I did that and it bent the condenser fins! Straightening them is a bitch. They break when trying to straighten. Just use a spray on detergent that helps loosen dirt, or something similar, and wash it off with an unpressurized hose.

 

Omg, finally someone is straight up with me. Thanks, this response really makes me feel more assured that the fans are the problem. I felt like I was the only person who had this problem. I'm just trying to find a time to do it thank you again.

 

ok ummmm
I'm happy that you are happy that you found someone that is having the same issue.
Great.
However, I don't believe this is a "common" problem with the fans "slowing down" per-say. I mean in any real sense that its not commonly discussed nor have I personally seen this issue.

But it makes sense. At idle is when you need your fans not at speed.
I guess like anything the fan motors wear out.

---pencils note in back of tiny brain ---

Ok Aston the burden of proof is on your shoulders.
You say it's a well known problem.

Please show the forum or something you have that indicates this is a known issue.
No really, how is it you know this. Just a gut feel or something?

 

No worries bro Just test them out and let us know the numbers. I agree with WCS. Put back the panels between the chassis and the bumper. Those stop air hitting the radiator from escaping from the top.

You must also seal around the radiator. Can you see bits of foam (sponge) on the sides of the radiator? That's where you need to seal. Cover it all up. This forces the air to go through the radiator. It also helps at idle, stopping the hot air from the engine bay leaking out to the front of the radiator, and getting sucked back in from the fans.

Sure. Why did Mazda change the fan motors in the S2? :P

The fans slowing down over time has been discussed on rx8club.com before. I will find those posts and quote them once I get on my PC. But anyways, at first, even I didn't want to believe it. I was under the impression that when fans fail, they stop spinning completely. But apparently that's not how ELECTRIC fans fail. They slow down over time. OP's fans are fast enough to cool the car at night, but not fast enough to cool it during the day when the ambient temp is higher. Makes perfect sense. His fans are not terrible. But just that tiny bit not fast enough.

The picture I attached is from the Factory Service Manual. 9k told me to read it, and my answer was there. That pic shows the amount of amps each fan motor pulls when new. Anything below the lowest value mentioned is FAILING. OP can wire the fans directly to the battery with a tester and find out for sure.

Most people don't notice it, because they don't live in hot climates. At night, when it's 80F outside, my car idles at 200F. During the day (90-100F ambient temp), when stuck in traffic, it climbs to 220F (and then I turn on the heater). That extra 10F is what kills it. So it's possible that most car's fans (including yours, though I hope not ) are just barely fast enough to keep it cool in 70-80F weather, but not in 100F weather.