I REALLY need some help here.

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emphasis on the really.

cliffs at end

im at my wit's fucking end and im super pissed about this vehicle.

99 Oldsmobile Bravada
4.3 chevy vortec engine
full time AWD (or 4wd whatever they call it)

coolant looked like and pretty much had the consistency of baby shit.

Overheated on the interstate at the beginning of the month.
took it to a shop, they diagnosed that the intake gaskets were trashed and needed replaced. ok, seems like that was a very common issue with these, so i got the problem solver kit from fel-pro.
had those replaced along with the t-stat.

the suv did ok on the interstate back from the shop. noticed it got hot at the lights afterwards.
took it and had a full flush of the system.

car still gets too hot.

on the temp gauge it should sit at about 210, which is exactly half on the gauge. theres a mark halfway between 210 and 260 (which is the highest the gauge goes, which i guess would be about 235).
the temp would read at about that 235 (3/4 on the gauge)
so, i replace the t-stat under warranty hoping to hell that we just got a faulty one.

the car wont go to the 260, it just goes to the 235.
still does it after t-stat number 2.

heres the kicker, it only does it on the interstate. driving around the city during the hottest part of the day and it does fine. when i hit the interstate it gets hot.

so, i talk to some guys i know that know chevys and whatnot, and we all agree that it could be the water pump. thinking that maybe at the high speeds with the engine riding higher rpm's, the water pump just cant move the water quick enough.

the check engine light was on, and one of the codes was for the coolant sensor low resistance or whatever. so, for 10 bucks, i wasnt about to just let it be. changed that too.

changed the water pump. still does it.
only on the fucking interstate.

drove it after changing the water pump and that sensor. on the interstate, it got up to the 235 mark. got back and stopped, and the coolant is boiling out of the overflow. nowhere else just overflow. shits hot.

also, what nobody else seems to understand either, the heater wont work. will blow hotter than shit air for about 10 seconds when first turned on, then goes to ambient. and stays there. no matter how long you leave it on.

i figured it couldnt be the fan clutch, bc its def going, sounds like a loud ass domestic suv. and it does great sitting still at idle, and cruising at slow speeds around town (55 and under) no matter how long i leave it sitting or drive it at city speeds.

car overheated.
changed intake gaskets, water pump, t-stat, coolant temp sensor.
still overheats but only at interstate speeds.
it cant be the fan clutch, because it does great around town sitting at stop lights.
boils in and from reservoir after interstate run.

the only thing i can conclude is the radiator must be clogged.

i just want some confirmation, or other theories because i dont want to work on this anymore. i want it to be over. working two fucking jobs, and spent one of my two days off this month working on this fucking car, not to mention one of the few evenings as well.
i mean, what the fuck else could it be? everything else has been changed. or am i missing something? i figure that baby shit coolant had to have just trashed everything up including the heater core.

i dunno. im about ready to wreck it for her and call it a day.
Did you put the tstat in backwards perhaps?

Or maybe you need a new radiator cap.
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t-stat can only go in one way. i thought of that while i was putting in the second one, i didnt put in the first. so i tried it just to see and the pipe is much smaller and wouldnt allow it to be put in any other way.

radiator cap is something to look into. id rather change that than the damn radiator.
How does the coolant look now since the flush? And I'm sure you did, but, did you change the oil a couple times after the initial incident to clear all that crap out?
the oil was changed after the intake gaskets were done.

the coolant in the system has looked good. there is still some ugliness to the reservoir because the walls were coated in there, but, the numerous times and various places i have had to open up and had coolant leak out, it looked fresh and new, which it is.

i just really dont want to put a radiator in it if its not going to fix the issue.

but, im debating on replacing the radiator, both hoses, and the cap tonight. thats all there is left to replace. i just dont want to go through all of that and have it still over heat on me. its driving me nuts.
Are there any radiator shops in your area? They can usually check them out for next to nothing.
im sure there is. how would they check it exactly? just use a laser thermometor to check for cold spots? its impossible to feel for them. there is no access to the damn thing from the front or back because of the ac condensor and the shroud/fan on the back. and when its up to temp, everything is just fucking hot. nothing hotter than the next as far as i can tell.
You'd have to pull it out. They'd pressure test it and check for blockages. If youre going to pull it anyway its not a bad idea. :shrug2:
yeah, i dunno, personally i feel if im going to pull it out i might as well replace it.

im not going to work on it tonight. im just going to take a night off and hopefully come across another thing or two to try easily before putting the cash on the radiator.

i need a night off.
Is your fan working? Not sure if you have e fans on that vehicle.

Remove said 4.3 and drop in 5.7 from a 96-99 Silverado. That or do an ls like horsepower tv did.
Its not an electric fan. But that can't be the issue bc it does great around town. Can sit and idle for an hour and not get hot.
transmission cooler routed through the radiator? transmission is getting hotter on the highway at higher speeds and using the radiator to try to cool it? Just a theory, I know some older cars utilized auto trans through the radiator.

If so, change trans fluids. When was that last done anyway?

Like I said, just a theory since you seem to be stumped.
yep. trans cools in the radiator.

would be the first that ive heard about that. good theory.

the more i think about it i keep going towards head gaskets. leaking a bit during idle, but not enough to cause a problem. but when the engine is steady at 2.5k rpm then it gases up the system.
with the symptom of the heater not working, im gonna take a stab and say you have a blockage in the coolant system, or an air bubble. try bleeding?
Does it have a plastic air dam underneath and is it now missing?

RX7's are notorious for the same issues and and it's almost always because someone removed the air dam for something then didn't replace it
everything that should be there, is there.

im thinking the same thing about the radiator.
was going to do a pressure test last night but the damn thing was broken. will be getting another today and trying it tonight when i get home. if it shows that its not holding pressure then i will be doing a compression test.

i just want to be positive before i buy something else.
Sorry if you stated but is it eating water/coolant??......I figured you'd see a leak.

Exhaust got white/blue smoke??
transmission cooler routed through the radiator? transmission is getting hotter on the highway at higher speeds and using the radiator to try to cool it? Just a theory, I know some older cars utilized auto trans through the radiator.

If so, change trans fluids. When was that last done anyway?

Like I said, just a theory since you seem to be stumped.

I vote this.
not losing any fluid that i could notice.

just got home and did a pressure test on the coolant system.

cap (new) holds at a solid 15psi, which is where it should be.
system was pressurized to 22psi per the instructions and it held it fine.
so im assuming its safe to rule out head gaskets? i left it on there for a good 5 min, and both hoses were solid with pressure. no leaks, no hissing, nothing. needle stayed put.
So......how is the transmission cooled? Is it through the radiator or does it have its own cooling? I know it was mentioned earlier. I have never seen an a/t that didn't have its own cooling radiator attached to the main radiator or somewhere on the rad support (although most of my a/t experience are hot rods and chevy pick-ups)