Hello everyone. A couple of weeks back I posted about a transient overheat issue on the dumb question thread. Car would stay around 212F fine at idle and then out of the blue, slowly climb up to 219. I don't know if it would've kept on climbing coz I turned on the heater at 219.

For more info on that, please refer to this link - https://www.rx8club.com/rx-8-discuss...08221/page169/

Post #4209

Most of you guys told me that it's probably a sticking thermostat, air or suspended debris in the system.

So I got myself a new thermostat and installed it, sealed it with sealant so coolant won't leak, drained the coolant from both the block and the radiator, flushed it with distilled water and put in fresh coolant (30:70 mix). Started the car with the radiator cap off and the heater on full to purge air out. I was monitoring the temps from the Torque app.

Temp slowly went up to around 185F and then started climbing fast to to 208F, coolant level climbed up and overflowed. A lot came out. My mechanic quickly put the coolant cap back on to stop it from spilling everywhere. So it went out through the overflow horse instead.

Kept idling. Coolant level kept dropping. We kept topping it off with distilled water until the coolant level settled. Turned off the heater and put the AC on. Fan 2 kicked in (the loud one) and the temp stayed at 194F. Turned off the AC just check the temp, temp went up to 206F. Turned the AC back on, temp dropped to 197F. Turned off the AC again and revved it up to 3000RPM for 15 seconds to purge more air out, temp went up to 212F and stayed there. Turning on AC dropped it to 210F, but then it went back up to 212F.

I must add that while we were doing this, my mechanic kept putting the radiator cap back on every few minutes. I don't know why.

As soon as I pulled out of the garage, I floored it a little (shifted at 4000rpm) and got it up to about 25mph. Temp shot up to 217F 2 mins after pulling out of the garage, I stopped at a nearby restaurant to get lunch, and as I was waiting in the car (AC on), the temp slowly climbed to 221F. I immediately got down and went to the front of the car to see if the fans were spinning, and they were!

Came back inside, temp was 222F. Turned the car off immediately. And then, weirdly, as i shut the car off, both fans turned off immediately. From what I know, they should stay on when the coolant temp is high. Fearing it'd overheat due to the coolant not circulating, I turned the key to the ON position. The fans turned back on, temp reading was 224F, few seconds later, climbed to 226F. I was peeing my pants

I then started the car back up, temp dropped to 221F within 5 seconds. Turned the heater on full, temp went down fast to 208F. Turned on the AC again, temp slowly climbed to 212F and stayed there throughout the 10 minute journey home.

I have no idea what's going on. I've run out of ideas here.

What worried me was that the fans didn't stay on when I shut the car off at 222F. Also, the loud fan (Fan number 2) did not come on while I was idling at the garage with the AC off. It was at 212F, but Fan 2 didn't kick in. Fan 1, however, was working. Fan 2 ONLY started spinning with the AC on.

What could be the reason for these crazy temp spikes? It's fine for the most part, and then all of a sudden, starts slowly climbing to 220+F

HELP!

 

Your radiator may be clogged beyond normal.

When it's hot, letting it idle is not the thing to do to cool it down. Thermal efficiency is at it's lowest, and no matter what you think about circulating coolant keeping the temps even (which is true) our flow from the water pump at idle is negligible. It's better to just shut down and wait.

 

I thought about that. I flushed the radiator today and everything came out nice and clean. No rust. No debris. The drain flow was good too. Thing is, it doesn't always overheat. It says around 212 just fine for most of the time, but randomly it'll climb to around 220F, when I turn on the heater, I'd drop back down and not climb up again.

What I'm trying to say is, it doesn't keep on climbing towards 220F all the time. This has only happened 4 times. Every other time, it stays cool

 

Did you bleed it through the top throttle body hose with the front of the car at a high angle, as the workshop manual says?

 

No. I did it with the radiator cap open on a level surface. Is that bad?

 

It's not bad, the throttle body method is just much more effective since that'sthe highest point in the system (even if the front end isn't elevated.

It's very easy, here!

 

Coolent system pressure test.

Temps climbing like you said is kind of normal. Idle doesnt move a lot of water. So it sits and heats up. When you drive it starts flowing and the hot water hots the sensor.

There was no reason to use rtv it has a gasket and you might have caused a restriction in your system.

If turning on the heater drops temps. Then its likely a radiator/air floe issue. Have you cleaned the radiator and ac condenser?

 

What year is your car? Does it have the heater hose orifice restrictor?

 

If the fans are working and the water is circulating then all I can think of is the air isn't moving through. Maybe the ac condenser is plugged up with dirt?

Scrub it with dishwashing soap and nylon brush then wash it out with a garden hose and see if anything nasty comes off.

Other option is that the water pump impeller has separated, or it's otherwise not pumping, but then your temperature indication would be sketchy and you wouldn't be able to lower temp using the heater.

 

I don't think I can remote the upper radiator horse, though I could take it back to the garage and tell them to do it. What if I just elevate the front of the car and do it with the radiator cap off?

Yes, I am going to pressure test the coolant for leaks. Around May last year, the rubber grommet under the air box fell down and jammed the fan, causing my car to overheat. I'm guessing it hit 245F, maybe. Although my car drives fine, it could be leaking coolant. IF it's pissing coolant into the chamber, can it overheat?

My car never used to go above 212F when idling. In slow moving traffic, it'd hit 215F and then drop back down slowly to 212F as I idle again.

The sealant was only applied on the outside of the thermostat and the radiator horse I removed to get it out.

These random temp spikes happened BEFORE I changed the thermostat and coolant as well.

No, I haven't cleaned the radiators. When I flushed the radiator, the water flowed out smoothly. I didn't find any corrosion or debris, so it seems to be fine.

Which brings me on to the fans. My fans work. But since the grommet jammed the fan, you think it could be spilling at a slower speed? It jammed the passenger side fan (Fan 1, right side of the car).

2007 AT with 30,000 miles. No orifice restrictor.

The radiator looks fine from the outside though. Wouldn't rubbing it with a nylon brush damage the radiator? I will try doing it. Getting there is the problem.

So if the pump is failing, I can't drop temps with the heater? Confirmed? I can rule out the pump then

The rubber grommet fell in and jammed Fan 1 (the one that stays on all the time). It didn't burn the fan or blow a fuse. Which makes me wonder, could that weaken the fan motor? Because it got jammed? Making it spin at a slower speed? Is that even possible?

 

The restrictor will help by allowing more water to go through the radiator and mot the heater core. The core will still get plenty. It will just stop recuriculating excessive amounts of hot water through the engine and getting hotter.

By cleaning i meant externally.

I don't have any ideas abt your fans.

You might be getting just a little blow by putting exhaust in your system and getting it extra hot. I think thats a small might.

Do you have the front middle splash guard and the foam on the sides of the radiator?


Its pretty easy to pull the bumper and have plenty of room to get in there and clean the ac condenser and radiator.

 

Only have phone

Fans.. both run at same speed, low or high. Sounds like fan issue. Ac on forces high. That explains temp down with an on.

Check congrats thread below. Foam around radiator and fans on low recommended.

 

Ok, I'll try cleaning it. Thanks a lot for that I'll let you know how it goes.

What exhaust blow? Are you talking about the catalytic converter heat moving forward and hitting the radiator?

Yes I have the splash guard and the foam.

But even with AC on, my temp goes up. I left the car idling for 20 mins while I was in the garage and it did not overheat. Stayed at 212F.

Heres what happened.

As I was l pulling out of the garage, the temp was 212F. Floored it to get up to 20-25mph. Temp went up to 217F. Cruised to a stop (around 500m from the garage, so all this happened within about a minute) to grab lunch. Left the car idling, temp went up to 222F I turned off the car and watched the temp go up to 226F. Started it back up and it went back to 221F immediately. Turned on heater on full and started driving home. Temp went down to 208F Turned AC back on. Temp slowly went up to 212F and stayed there throughout the journey (about 2miles, 10-30mph in backroads).

I will seal around my radiator tomorrow when I take the bumper off to clean it and let you know how it goes

 

You shouldn't be anywhere near 212 in regular city driving or idle. 180-190, but not over 200.

I'm with Legot on this, you have a clog somewhere that's preventing proper circulation of coolant away from the engine. The fact that the temp rises from stable 185 (thermostat-controlled temp) to 212 (beyond thermostat control) rapidly tells me it's something after the thermostat in the flow. RTV could definitely do that, but that wouldn't explain why it started in the first place. Was other work performed on the cooling system since the car was built? Was the engine replaced?

Silly if true, but check that no hoses are kinked/twisted.

If you really want to rinse out the rad, you need to do this in the direction opposite the flow of coolant, meaning take the rad out of the car, turn it upside down, run water down the output.

To the point about exhaust, he's talking about a breach in the water jacket seal that allows hot gases from the combustion chamber to enter the coolant. If you leave the rad cap off, do you see bubbles coming up? Is there goo of any kind around the underside of the rad cap?

Small chance but maybe repeat your thermostat install, this time without RTV. It's probably not the root cause, but it's probably not helping.

 

collapsing lower rad hos

 

Collapsing radiator hose is a good possibility. I would think thats more of a high rpm problem.

At idle the car does not move a lot of water. So it heats up but the really hot stuff might nit be moving through the system. So as soon as you start driving the temp will raise as that hot water surges through the thermostat to the radiator.

The ac might help the fans but it adds extra heat right in front of the radiator so it does not work as good. It also causes additional load which will produce more heat.

 

I forgot to add that it's 92 degrees over here. From what I've heard, most RX-8s idle at around 210F+.

The temp does not rise rapidly from 185 to 212F. It only climbed to 208 or so rapidly while I was purging the air out after changing the coolant yesterday. Otherwise it has never done that. Temp goes up gradually.

I don't think RTV did that, because these temp spikes used to happen before changing there thermostat as well.

No work done on the cooling system. Original engine.

By rinse you mean clean the outside of the radiator? If there is a clog, wouldn't try to overheat all the time? I just came back from a drive. Ambient temp was 80F. Car hit 212F once while flooring it, and then while I was idling, it gradually went down to 203F.

The only time I left the radiator cap off was yesterwhile while purging the air out after putting in new coolant, and I think I did see bubbles. But that was probably just air in the system. No goo under the coolant cap. It's clean and looks new.

What does that mean sir?

Thanks for clarifying that. The weird thing is, my coolant temps DROP when I turn on the AC :/

 

--UPDATE--

I popped the hood today and noticed I had lost a bit of coolant. Maybe I still had some air left when I left the garage yesterday and as it came out, the temp went up to 226F. Can that happen??

I topped it off and went for a drive. Ambient temp was 81F. Car stayed at 194F most of the time. In slow moving traffic it would climb to around 208F, and while idling, drop down to 203F. Floored it once to get up to 30mph. Temp went up to 212F. I had to pull over a few seconds later, and while I was idling, temp slowly dropped down to 202F.

Everything seemed to work fine today. Didn't even go close to 220F.

I don't know what's wrong with this car. One minute it's fine and the next minute it's overheating.

The other thing I wanna ask you guys is, I know that when the car is hot, the fans stay on even after taking the key out of the ignition. At what temp does that happen?? It USED to happen before the grommet jammed the fan and overheated, but now the fans turn off immediately. At times they'd stay on for 5 seconds max after taking the key out. Maybe when the fan got jammed, it messed up the fan relay?

Could it be possible that my fans are not spinning fast enough? Could it be that the fans are fast enough to maintain the coolant temp at 212F, but if it goes up to say 215F, it struggles to get the temp down?

 

Well you haven't changed anything, so nothing has changed :/
Start going through the suggestions/questions in this thread, one by one.

Fans can be damaged, but they usually work or not, being "slow" isn't really a thing. But anything is possible, video would help.

That fact that you've lost coolant isn't amazing, could point to a water jacket breach. How much did you lose over what time period?

 

My fans are working. I'm just worried that the one that got stuck might have gotten slow. What kind of video?

Well the grommet jammed my fan and the car overheated (I'm guessing it went up to around 245F) in May 2014. Since then I haven't lost coolant at all. Coolant always stayed at the Full mark.

It's only after the coolant flush I lost a bit of coolant. Could be that I had some air while leaving the garage that day? And that bit of air came out while I was driving? And while it came out, it caused the temp to go up to 220F?

 

I got a real keyboard..

I suggest 2 mods from the Congrats Thread. First, foam around the radiator. You can do this from inside, and reaching through the front. This will keep the fans from just cycling hot air. They WILL blow air into the engine bay, on HI, the air cannot get out of the engine bay, and leaks forward back in front of the radiator unless you are moving at a fair clip. This causes a temp spike when the fans switch to high.

Second, fans on low. This is a simple as wrap a small piece of wire around one spade terminal on a relay. To be sure, drop a bit of solder on it. Then plug it back in. Run this way all summer. You will see the temps stay close to the thermostat point. Otherwise, unless the AC is on, the fans do not come on until after 200.

The fans run on 2 speeds, low or high. They both run the same speed.

 

What switches the fans to high?
Is there a switch or relay of some type that could be bad, possibly related to the fans not staying on after turning off the ignition?
I know on hot days after a hard drive mine would stay on quite a while.

 

It's 90 degrees over here so the AC is on 24/7 I will definitely seal around my radiator. I'm also gonna do the fans on low mod. The weird thing is, I know that the fan turns on at 207F. But I think my Fan 1 (Passenger side) stays on all the time. AC on or off, it stays on. When I bring my ear close to the bumper, I can hear it. I can even feel the air blowing. The second fan (Fan 2, driver side) comes on when I turn on the AC. I'm not sure if both fans spin at the same time.

At what speed does the fans turn off while moving? 20mph?

Also, how high should the coolant temp be for the fans to stay on even after shutting the car?

That's exactly what I'm thinking. Maybe since my fan got jammed once, it messed up a relay?

Can anyone here say if it's possible or not? I have no idea how these relays work

BigCajun, do you monitor coolant temps? Do you know what the coolant temp should be for the fans to stay on after shutting the car off?

 

No, sorry. The only time I watch them is on the hottest days, especially if I'm at a standstill.
Can't tell you what temp activates the prolonged fans after the ignition is off.

 

I know if you pull cooling fan 3 relay they'll go off of high. I think 2 will do it also.