Michael Stillwagner

I have an issue. My 2000 chevy c2500 5.7l vortec is pushing coolant into the overflow tank but not bringing it back into the radiator. I get bubbling int the overflow even at cold temp from sitting over night. I have to constantly take the coolant from the overflow and return it back to the radiator manually. what could cause this? I recently rebuilt the engine new head gaskets (heavy duty set), new water pump, and so on. Did I manage to do something wrong or mess something up when I ran the Valvoline super radiator cleaner through the system? the vehicle did not do this until after the coolant cleaner stuff was ran through it.

shbox

Has this thread just turned into a catch-all for all vehicles?

Michael, you might have a hole in the pipe or hose that goes from your radiator to the overflow. Of course, I don't know anything about your vehicle's cooling system. This is an LT1-LT4 forum.

HellTeeOne

This. I've made the same mistake before.

cali962

can someone post a pic of these two lines cause I'm not gonna lie I'm hella confused and I am a novice at this

ACE1252

Describe your problem. This is someone else's thread. Are you having the same problem? Have you had the system apart recently?

cali962

Same problem with the coolant boiling into the reservoir, new radiator, fixed fans both work properly now, new cap tried bleeding the system multiple times and it keeps boiling into the reservoir so I'm thinking maybe the hoses are flipped I just dont know exactly which ones they are that's why I was gonna see if someone can show me the hoses

ACE1252

There is a small hose connected to the neck of the radiator and another small one below it. The one connected to the neck should go to the overflow reservoir. The one below will come from the throttle body(95-97) or if you have a 93-94, the head steam pipe(or if you did the throttle body bypass mod...worth a couple of hp due to cooler throttle body),

http://shbox.com/1/93-94_hoses.jpg
http://shbox.com/1/95-97_hoses.jpg

cali962

I have a 97 trans am, the hoses are correct a checked them is there anything else that could make the the coolant boil into the reservoir

ACE1252

Blown head gasket, cracked cylinder wall, cracked head.

A cooling system pressure tester can help diagnose if the cooling system is being pressurized by the above. Hydrocarbon testing of the coolant as well.

Just to be sure, double check to make sure you have not got them backwards. Trace them out.

cali962

Thanks for the help I'll test the system and hope for the best any advice when testing it

ACE1252

Is the reservoir completely filling up?

cali962

Yup boils all the way to the top and spills over

Bengtson95

this guy is right! I had the same issue for so long I almost sold the car. Everytime it got up to temp it would bubble out of the overflow, I did a waterpump job and switched the lines....also for some laughs I brought it to Firestone and they said my motor was blown and I needed a 6k crate motor lmao.

cali962

Ok so update I pressure tested everything and found several hoses leaking fixed everything, but the coolant still boils out of the reservoir, I just pulled out the reservoir and there are no holes in it just to be clear I have a 97 trans am , and the throttle body hose goes to the lower hole on the radiator and the upper one goes to the resivour right ???

Bengtson95

You are correct with the hoses. Upper=overflow

ACE1252

The one on the radiator neck goes to the reservoir(just below the cap). Make sure there is no damage or build up in the inner sealing surface of the radiator neck. The cap might not be sealing.

How fast does it fill up? Really quick? Before the engine gets warm?

cali962

Soooooo new update rechecked the hoses everything is tight, put the reservoir back in , put new coolant in it, and tried bleeding it with the coolant bleeding funnel and the coolant just boiled out on the funnel, I also tried testing the block and the dye didnt change color stayed blue, so I figured the block was good then that happened so now even though the block tested fine I'm starting to believe that it's not fine and maybe the gasket is blown

chronos

It might be worth checking the rad cap again. I had a 1-year old AC Delco cap go bad. The smaller spring went bad, so it seemed OK but it was letting coolant get pushed into the reservoir. It didn't do it all the time, so I suspect that maybe it was only letting coolant into the reservoir at "low pressure" and later the pressure would rise enough to seal it closed.

SS RRR

iTrader: (2)

Once you fixed the hoses, did you keep pressure on the system for approximately 15min, and if so, did the pressure remain consistent? If not, take the spark plugs out of the block and do a 15min test and then rotate the engine to see if coolant starts spilling out of one of the cylinders. Make sure the pressure is at the rating of the cap, which is 19psi, I believe.