Radiator won't hold coolant.
 

I know there are a lot of other threads out there regarding this issue but I've never read one that was specific to my issues. It IS a firebird v6 but all cooling system issues are basically the same be it v8 v6 or God forbid a 4 cylinder. So far it seems the whole cooling system is failing. About a month ago the stat went, it had a small pin hole in it. 3 weeks later the radiator cracked. Now it's the heater core!!

For a week I've been trying to figure this out. After I put my new radiator in. I filled it all up 50/50. It drove amazing for 3 whole days. Then the 4th day it over heated. I let it cool off and drive home and there let it sit for a while. I opened the radiator cap and coolant only half way filled the tank... so I top it off. Next day. Drive it. Does fine the whole drive but when I put it in park, water/coolant starts to come out of the overflow. Just enough to where it empties the radiator to half but never more than that. And I notice that right before it does this the temp goes from 208 (n.o.t) to 212 (boiling point) then after half comes out it goes BACK down to 208 and never overheats again.

So since all it does when I fill it up is blow it out the overflow till it's half way I Was thinking head gasket but I found out from the wet carpet on the pass. Side that my heater cores bad. Would a bad heater core blow coolant/water out of the overflow like that?

Sorry it's such a long post. Just trying to get to the bottom of this mess. Feel free to ask any questions. I'm going next week to get it pressure tested. Any help would be great. Thanks!

When you refilled it, did you have the front end up on ramps or jacked up??? That's what I did when refilling the radiator. I could be wrong but you have may have air trapped in the system.

That's exactly what I was thinking until I found the bad heater core but no I did not have the car on an incline

You have a cracked head, block, or bad head gasket. Things are going bad due to combustion pressure entering your coolant system.

My money is on you having the wrong type of radiator cap or a bad radiator cap, which is not:
- pressurizing the system properly
- releasing the vacuum that builds up on cool-down and causes stuff to crack

What kind of cap to you have?

this would be my guess as well. Had this problem before on a v6 before I traded it in and the cap didn't exactly work well with the new radiator for some reason.

I got one of those aluminum locking radiator caps. Should I put my old one back on and see what happens? If it doesn't work are we looking at a head or head gasket? It wouldn't seem to be a bad gasket or head cause it's not overheating. It just won't hold the proper amount of coolant.

That's a problem.


Yes.


Probably not. A head gasket issue would give you problems 100% of the time.

Okay. I will put the old one back on and see how it runs. I'll let you guys know the verdict.

If that doesn't work, the 3800 is known for intake gasket leaks and those plastic coolant elbows cracking/breaking. I had a 3800 car I was hard core about before I got my z28.. lol

I've replaced the plastic elbows with the aluminum ones already. Haven't checked into the intake gasket.

Okay I put the old cap back on and drove it and it didn't help actually it's stayed at 212 the whole time and actually started smoking and running rough. Waiting to cool down to check the coolant level. Any ideas?

Edit: coolant level went down to half way again. No signs of leaking anywhere except what comes out of overflow. This has me blown away honestly. Why would the car smoke at 212?

Is this after it has cooled down? If so, this would indicate that you aren't getting a siphon to suck the coolant back from the overflow as things cool and contract. If this is the case, then the cause may be why the system isn't holding pressure. This could be why things are boiling and overflowing. (The system should pressurize, which will raise the boiling point of the fluid in the radiator and keep the fluid in.)

No. Coolant doesn't seem to over flow unless the car is at 212 and on. Could be irony but it seems it doesn't overflow until the car is still, or at idol. Does coolant circulate through our engines intake manifolds? Might be coolant in the oil. Kind of too early to tell, just changed the oil like 500 miles ago

212° F is the boiling point of water. If the radiator is boiling over at this temp, it means your cooling circuit is not pressurizing properly. Pressure is what raises the boiling point so that the coolant/water mix stays as a liquid and doesn't turn into a gas (boiling). You can try to run a pressure test on the system when cold. Maybe you will find the leak?

Since you aren't in the "red" with regard to temperature also would look to a pressurization issue first.

Still/idle issues usually arise from fan problems. Are your radiator fans working?

I am taking it to a shop to get it pressure tested probably tomorrow. Radiator fans are working but idk if they are working right. Neither come on until I turn on the ac. But it hasn't ran hot so idk if they'd cut on if it got hot.

Been reading a little bit and found that the lt1 radiators have an "extra nipple" that you need to cap off. I didn't know this and I had my wife helping me with this and told her to plug the overflow hose back to the new one. Not sure if she put it in the right spot or not. If I had to guess I would say no. It seems like that bottom nipple would be pressurized which would pressurize the overflow. Attachment 566255

I am more familiar with the LS1 plumbing, but I think this should be universal to ALL radiators: the overflow tank hookup should always be the top-most nipple on the radiator. The radiator cap keeps the pressure from reaching the overflow tank unless it exceeds the limit, and allows vacuum to suck coolant back in when things cool off. If it is plugged in below this, that would create the pressurization problem.

That top nipple goes to the overflow! If not, the radiator cap can't do it's job...

The bottom nipple is probably for the vent line.