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Dammit. After finally wiring in the second coolant sensor I thought I had my fans/coolant sensors sorted and even made sure fans turned on, but somehow maybe something still isn't right. Driving home on the hottest day so far, and my temp gauge starts to climb at the light. I'm like WTF. I roll and it goes down. However as I'm almost home, it's climbing up again even while I'm driving...then stops and stays steadily at 3/4 way up the gauge.

I pull over and pop the hood. Coolant is gradually dumping into the overflow. Ouch. The main fan is running full on, however the secondary (condenser) fan is trying to run, but can't. It spins up, but then turns off almost immediately. And the four-relay cluster is clicking like crazy. So obviously the ECU is trying to control it, but something is conflicting... Obviously it's a damn hot day and running one fan is not enough. Maybe the secondary coolant sensor is sending bad signal and turning the fan off. I'll be getting a new one. It doesn't seem like there's actually a problem with the fan motor or anything of the sort. I'll look into it some more.

As I checked under the hood and the car idled, the temperature gauge went back down to almost middle, but wouldn't quite get there. The main fan would turn off when it was slightly above middle, and then turn on again as it would start climbing. I shut the car off, let it chill, and then checked the coolant level - it was full, so at least that's good.

But now I'm worried that driving hot may have warped my heads or damaged the head gasket... I checked the oil, and it looked clean and free of coolant. Gonna do a compression test tonight.

I'm not really sure how hot the motor has to get in order for damage to occur...

It has to get really really hot! I blew my rad hose on the approach to red deer, made it home 5-10 minutes later with not a drop of coolant in the engine... Replaced the hose, topped it up, and same thing no coolant in the oil. I'm sure you'll be fine bud!

10 minutes with no coolant? That's kind of extreme...

it sounds like you should be ok as far as damage to the engine, and really as long as your engine has coolant and is cycling it through then you should be ok. is your rad in rough shape at all? try replacing your thermostat.

one main fan should be enough to cool your engine. im pretty sure only the ones with ac came with the second rad fan. maybe the clicking from the relay means its fucked?

Hmm...I even remember somewhere in the manual it listing ECU using both fans above certain temperature, even when A/C is off. Radiator is in ok shape... One fan usually does the job, but after driving for a while it does get kind of hot in the engine bay what with the headers and everything, and I can see how in 90 degree weather one fan might not be enough. Pretty sure the coolant cycles, I redid the coolant system not too long ago, . I'll try the MX-6 ECU and see what that does.

Alright, I did a compression test, and I'm getting around 190 on all, maybe a bit lower (I think normal compression for ZE is 200-210). Putting a bit of oil in the cylinders brought the compression way up to over 210. So I'm not sure how to interpret this. If this is a sign of worn cylinders, pisons and rings, then that's ok, because it's expected and I should be ok.

I'm not sure, but I think if the heads were warped or gasket was bad I'd get readings that are way worse, yeh? And I'd have coolant in my oil and oil in my coolant...

Yea you're fine, nothing got damaged from what you said.

BTW, after hooking up the KL85 ECU (which only uses one coolant sensor), seems my fans are functioning correctly now. No crazy relay clicking or any of that business. Temperature stays slightly below middle... Let's hope I'm set.

i had almost the same prob but kinda similar bro then just out of know where blew two heads cuz my k8 kept over heating

Well after 5 days with the new parts my fluid is still on high. Guess I dodged a bullet there.