So I'll try to make this as short as possible.
I bought my c5 vette in pretty rough condition, I wanted to change out all the fluids and get the ac working.

I did a coolant flush as there was very old crusty almost gel like coolant in the reservoir before (you could scrape the coolant off the sides of the walls with your finger) I did a chemical flush and a vacuum refill. I started overheating. I replaced the thermostat, water pump, upgraded to a ecp radiator, flushed the coolant again, vacuum filled it, tested for a blown headgasket with a block test (comes back negative) and did a compression test (numbers were in the high 190s and low 200s) , fans come on just fine and both work, I cleaned out the condenser and radiator with a pressure washer and compressed air, at this point I feel like I've done everything I know of what to do I even brought it to a shop and they just did another coolant flush and changed out the thermostat AGAIN! I just want to sell it at this point what do I do!!!!

 

are you sure all the **** is out of the heads and water is flowing as it should?? sounds like a blockage somewhere....

 

Sounds like someone mixed Prestone (green) with Dexcool (orange) coolant. These chemicals are incompatible and turn into goo. Keep flushing the system with water until the gunk clears out. This will probably take several fill-run to hot-flush cycles. Also, make sure to follow the procedure for burping the air out of the system.

 

Does the car have the front air dam on it? Just asking cause you said it was in rough shape

 

Should I do another chemical flush with blue devil?

 

I have seen that these have very specific burp procedures which I why I use the vacuum dealership fill tool

 

I dont know what the air dam looks like but I can prob check on google?

 

I have no idea how many flushes it will take to clear out a blockage if thats what you have going on....that **** gets everywhere

 

I doubt this is your problem because you say it overheats no matter what, sounds like a coolant flow issue rather than an airflow issue

air dam , 3 pieces under front fascia....big middle piece and one plastic piece on each corner

 

I mentioned the air dam because he never said if it’s overheating while driving or just sitting👍

 

yep....

 

it overheats during both but typically does a lot better at idle then it does while driving, I've been able to take it on days below 100*F outside on a trip to LA for 2 hours straight with ac off and it was just fine. The moment I turn the ac on it begins to rise.

 

Moved to C5 Tech.

 

I'm new to this website what does moved to c5 tech mean?

 

this thread is now in the C5 Tech section as opposed to the C5 General section. nothing changed otherwise

 

 

what temps is it running?... many people think these cars are overheating when they are perfectly normal for the way they are designed... just wanted to rule that out so you don't keep chasing your tail

 

+1 make sure your air dam is intact, second, i didnt see you mention what temps you are running at. LS1's run hot from the factory, so much so 99-02 Camaro/FIrebirds had dummy temp gauges, word on the street was GM got tired of people bringing the '98's in for overheating ... I would also research how to fix the gel like coolant issue caused by mixing types

 

just what is was thinking, normal operating temps are as follows: from the FSM Factory fan temp settings are low speed on at 226 degrees and off at 219 degrees. High speed on at
235 degrees and revert to low speed at 226 degrees. As stated both fans run at low speed and high
speed and fans are commanded off by the PCM when the vehicle speed exceeds 35mph.
You can force low speed operation at 185 degrees by turning on the AC. High speed operation with
AC on is still 235 degrees.

 

Oh-Oh!!!! The early Dexcool would coagulate/congeal into a somewhat jello like substance. If this has happened, you'll almost certainly need a new radiator, and who knows what else. I knew a radiator shop owner who made a lot of money off owners of cars made in the 90s that never changed their coolant. I guess the new stuff is reformulated and doesn't do this any longer. This was 15-20 years ago, so maybe someone with more current info will chime in. They may have some sort of flush chemical out now that can clean it all out of the cooling system. You’ll have to search. Hope this helps some, and good luck.......

EDIT......I see you have a new radiator. You may need to flush the heads and block with some sort of pressure, or chemical. It would help us, as others have posted, if you would post the coolant temps you're seeing. Also, do you know whether you have a 25% underdrive pulley/balancer? I'm just grasping here, because you've flushed twice, installed a new radiator AND water pump, so.....Hopefully, that jello crap coolant hasn't already plugged up your new radiator. Please keep us informed.......