I recently did a coolant flush on my new 96 LT1 to attempt to solve overheating issues, and trying to burp to coolant system but having trouble. I used the bleeder screw when filling up the radiator, and when I shut off the engine after reaching operating temp, the overflow tank gets filled. As it cools down it doesnt pull any coolant in from the radiator tank and when opening the radiator cap again it looks full. I can run the engine again and it will stay around 220F, but after a few heat cycles it will start to overheat so I shut it off and open the bleeder screw and a ton of air comes out to the point where I have to stand there for a solid 5 minutes waiting. It sounds like that would be what it needed, but as I let the engine completely cool, again it does not pull any coolant from the overflow tank and again when I open the radiator cap it is still "full." I even tried using a no-spill funnel, and some bubbles do come out, but not much, and eventually it just starts overflowing without ever adding coolant. I already did a test for exhaust gasses in the coolant system but it didnt show anything. Any idea what might be happening? Thank you.

 

So basically do what I did with the no-spill funnel but this time have someone increase the rpm to counteract the rising coolant level? I might have trouble doing that since I'm also having issues with a bad knock at higher rpm... Maybe I could just use a turkey baster to try and suck coolant out as it's overflowing? Thank you for you help

 

This is another thread about a 96 with the same thing.
https://www.corvetteforum.com/forums...ng-system.html

 

Maybe head gasket or maybe the water pump is bad? I’ve flushed my coolant twice on my 93, second time I was nowhere near as careful about the process and still had no issues either time…

 

Possibly a bad rad cap or surge tank. Either of those can cause air to get drawn into the engine as it cools instead of coolant from the overflow reservoir.

 

When I do mine I leave the cap off and let it warm up while squeezing the upper radiator hose to burp the air out. Once it starts to overflow put the cap on and all is good to go. Ensure that the overflow tube to the jug is clear as it could be clogged.

 

I found that the hose inlet into the plastic overflow tank was plugged with the crap GM used to put into radiators/coolant. This was on a 12,000 mile car that we bought in 2016 ! See if that inlet tube is plugged up as mentioned right above.

Also how many miles ? Have you checked to see if there is any bubbling in the coolant when the engine is running ? How about the radiator hoses. Are they hard after it cools down, like they are pressurized ?

 

yes good cheap/easy idea too, to check before suspecting pump, head gaskets rtc. You can also get the test strips to test the coolant for exhaust gases.

 

Have a brand new rad cap and overflow tank. Possible that it isn't an air tight connection though... But wouldn't that just make the radiator look empty when I open it? When I open it after it cools down the rad is completely full even though a ton went to the overflow tank.

 

Not sure how many miles because the center screen doesn't work (it's a project car) but the system was definitely in rough shape and I had to flush it a couple times.

There's no trickle of bubbles but instead just big bubbles, and those are only visible when using a no spill funnel because it overflows a lot before the thermostat even opens, and those bubbles don't counteract the rising coolant so I eventually have to shut it off before it overflows even with a no spill funnel. Hoses aren't pressurized after, if anything there's a vacuum because they'll be slightly collapsed and I can feel a little suction when opening the radiator cap. Radiator cap and overflow tank are brand new.

Also checked for exhaust gases and there aren't any and compression test on the cylinders all came back fine. One was a little low but still within spec according to the service manual (within 70% of highest pressure cylinder)