Hi guys, new to this form so bear with me here.

I am about to type out the history of my situation so I apologize if its lengthy, figured it'll only help pin point the issue better.

Boosted NA6,104xxx miles, FMU, 7-8 lbs.

So I did a coolant flush and new lower temp thermostat change back in March-April. I ran some water/radiator flush for the next week or so to clean out my cooling system further. During that week I decided to go to the lake (hotter temperature day). On the way back, my thermostat gauge was TAPPED out to the max with smoke coming from the engine bay. Of course as expected, I was boiling the WATER/radiator flush mix which must've also fried my water pump (Water dumping from the crank). Month or two later of the car sitting I install a new water pump/timing belt/all the recommended seals and components etc they recommend while you're in there and of course I put actual coolant in at this time. Car seems to be fine again but I noticed that after about 30-40 minutes of normal driving, the thermostat gauge would start to creep up and stay at about the 3/4 mark of the gauge and my 60/40 coolant to water mix would start to boil. After ignoring this issue (I know, stupid, I still shouldn't even have been driving it knowing that), I decide to go on a longer cruise. About an hour into it, my thermo gauage is tapped out, engine bay smoking, coolant boiling, and then my radiator decides to blow up at the plastic trim on top of the radiator. So then I go grab the radiator out of my parts car to go swap it in real quick and drive it home. Next thing I knew, same darn thing happens again and I blow up my spare radiator in the same spot. I know, crap.

I should mention BEFORE any of this happened, the car had NEVER overheated. Hard driving, drifting, donuts, whatever, it never overheated before all of this.

So my question is, what the hell is going on? Did I blow the head gasket with all the overheating? Did I warp/crack a head? Some other underlying issue? Bad thermostat?

Summary of the symptoms I know:
- The car tended to stay cooler longer/not over heat as much when the outside temperature was cooler
- The car tended to stay cooler longer/not over heat as much with "normal driving"
- The car tended to stay cooler longer/not over heat as much with the hood completely off
- The car didn't overheat one bit before I did the radiator flush and blew out my water pump running water in the cooling system
- I've opted out lack of air flow or the aero or undertray issue because like I said it never did this beforehand
- Car doesn't overheat till about 30-40 minutes of driving
- Coolant is boiling even with 60/40 mix
- Coolant boiling is causing too much pressure and keep blowing up my radiators
- I should mention, I did expand my exhaust to a 2.5" straight pipe all the way out to the rear after the downpipe during the week of my radiator flush. I don't know if that makes a difference but figure I'd ad that in there.

I'm currently thinking its either a blown head gasket, cracked or wrapped head, bad thermostat, gunky cooling system, or I don't even know what else.. What do you guys suggest? Thoughts?

Thank you

P.S. Yes I have looked through some other "cooling treads" to try to narrow down my issue but I would like to see if anybody has experienced this similar scenario and what it exactly it may be

 

Stop driving the car and trying to diagnose issues. See if it idles fine in the driveway. Look for coolant leaks. I don't think most cooling issues would take 30-40 minutes to appear besides gradually loosing coolant.

 

Leakdown test.

--Ian